AI Trajectory

null

{
  "EnableConfigs": [
    "BINFMT_MISC",
    "USER_NS"
  ],
  "FocusSymbols": [
    "bm_register_write",
    "bm_entry_write",
    "bm_evict_inode"
  ],
  "Reasoning": "The patch introduces a new sysctl limit `max_binfmt_misc_interpreters` to restrict the number of pre-opened interpreters in `binfmt_misc` using `ucounts`. This is a functional change to the core kernel and `binfmt_misc` filesystem that is reachable from userspace by unprivileged users (in a user namespace). Fuzzing should focus on the registration and removal of `binfmt_misc` entries to test the charging and uncharging of the budget.",
  "WorthFuzzing": true
}

null

{
  "PatchDiff": "commit abe853e3c93c8c19de2ae2375fa767eb5bd35667\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate:   Mon Aug 3 14:46:47 2026 +0000\n\n    syz-cluster: applied patch under review\n\ndiff --git a/Documentation/admin-guide/binfmt-misc.rst b/Documentation/admin-guide/binfmt-misc.rst\nindex 622b5d8c89957..d26b63a27c259 100644\n--- a/Documentation/admin-guide/binfmt-misc.rst\n+++ b/Documentation/admin-guide/binfmt-misc.rst\n@@ -128,6 +128,11 @@ There are some restrictions:\n    named by an absolute path. It is opened when the binary is executed, so\n    a relative one would be resolved against the working directory of\n    whoever runs the binary\n+ - the amount of pre-opened interpreters by ``F``, or bound to a ``B`` entry\n+   is limited by the ``/proc/sys/user/max_binfmt_misc_interpreters`` sysctl. A\n+   registration past the limit is refused with ``-ENOSPC``. This limits an\n+   unprivileged namespace pinning files. A nested namespace can raise only its\n+   own limit and every ancestor is charged too\n \n \n To use binfmt_misc you have to mount it first. You can mount it with\n@@ -215,10 +220,9 @@ with the credentials the entry file was opened with, exactly the way ``F``\n pre-opens a static entry's interpreter; the paths must be absolute. The\n path is everything past the first space, so there is nothing it cannot\n express, and no interpreter has to fit in a register string. An entry\n-binds at most 100 interpreters; a write past that is refused with\n-``-ENOSPC``. To bind a file that has no path of its own - already\n-unlinked, a ``memfd``, or reachable only in another mount namespace -\n-open it and write ``/proc/self/fd/N``.\n+binds at most 100 interpreters, and each one is charged against\n+``max_binfmt_misc_interpreters`` like any other binding. A write past either\n+limit is refused with ``-ENOSPC``.\n \n The ``load`` program then selects one per exec by name with the\n ``bpf_binprm_select_interp()`` kfunc, and every exec runs a clone of the\ndiff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c\nindex ad8c4f64bf102..a3aa42fd57614 100644\n--- a/fs/binfmt_misc.c\n+++ b/fs/binfmt_misc.c\n@@ -289,6 +289,7 @@ static void entry_put_interpreters(struct binfmt_misc_entry *e)\n \tlist_for_each_entry_safe(interp, tmp, \u0026e-\u003einterps, list) {\n \t\tlist_del(\u0026interp-\u003elist);\n \t\tclose_interp_file(interp-\u003efile);\n+\t\tdec_ucount(interp-\u003eucounts, UCOUNT_BINFMT_MISC_INTERPRETERS);\n \t\tkfree(interp);\n \t}\n }\n@@ -307,7 +308,8 @@ static void entry_put_interpreters(struct binfmt_misc_entry *e)\n  * The caller has to have validated @name and @path, established that @e\n  * cannot be matched yet, and owns @f until this succeeds.\n  *\n- * Return: 0 on success, a negative errno on failure\n+ * Return: 0 on success, -ENOSPC if the entry is full or the binder is out of\n+ *         UCOUNT_BINFMT_MISC_INTERPRETERS budget, a negative errno on failure\n  */\n static int entry_attach_interpreter(struct binfmt_misc_entry *e,\n \t\t\t\t    const char *name, const char *path,\n@@ -315,22 +317,32 @@ static int entry_attach_interpreter(struct binfmt_misc_entry *e,\n {\n \tsize_t nlen = strlen(name), plen = strlen(path);\n \tstruct binfmt_misc_interp *interp;\n+\tstruct ucounts *ucounts;\n \n \tif (binfmt_misc_find_interp(\u0026e-\u003einterps, name))\n \t\treturn -EEXIST;\n \tif (list_count_nodes(\u0026e-\u003einterps) \u003e= BINFMT_MISC_INTERP_MAX)\n \t\treturn -ENOSPC;\n \n+\t/* The binding keeps a file open, so charge it to whoever binds it. */\n+\tucounts = inc_ucount(current_user_ns(), current_euid(),\n+\t\t\t     UCOUNT_BINFMT_MISC_INTERPRETERS);\n+\tif (!ucounts)\n+\t\treturn -ENOSPC;\n+\n \t/* One allocation, both strings in it, like the entry's own buffer. */\n \tinterp = kmalloc(struct_size(interp, name, nlen + plen + 2),\n \t\t\t GFP_KERNEL_ACCOUNT);\n-\tif (!interp)\n+\tif (!interp) {\n+\t\tdec_ucount(ucounts, UCOUNT_BINFMT_MISC_INTERPRETERS);\n \t\treturn -ENOMEM;\n+\t}\n \n \tinterp-\u003epath = interp-\u003ename + nlen + 1;\n \tstrscpy(interp-\u003ename, name, nlen + 1);\n \tstrscpy(interp-\u003ename + nlen + 1, path, plen + 1);\n \tinterp-\u003efile = f;\n+\tinterp-\u003eucounts = ucounts;\n \t/* Publish the node: a lockless cat may be walking the list. */\n \tlist_add_tail_rcu(\u0026interp-\u003elist, \u0026e-\u003einterps);\n \tpr_debug(\"register: interpreter: %s {%s}\\n\", name, path);\ndiff --git a/include/linux/binfmt_misc.h b/include/linux/binfmt_misc.h\nindex 072e4b3dd78d2..8045b10dd3e5c 100644\n--- a/include/linux/binfmt_misc.h\n+++ b/include/linux/binfmt_misc.h\n@@ -7,6 +7,7 @@\n struct bpf_prog;\n struct file;\n struct linux_binprm;\n+struct ucounts;\n struct user_namespace;\n \n #define BINFMT_MISC_OPS_NAME_MAX 16\n@@ -21,6 +22,7 @@ struct user_namespace;\n  * struct binfmt_misc_interp - an interpreter an entry was registered with\n  * @list: link in the entry's list, in registration order\n  * @file: the file, opened at registration and never resolved again\n+ * @ucounts: the UCOUNT_BINFMT_MISC_INTERPRETERS charge the binding took\n  * @path: the path it was registered under, used as the name the interpreter\n  *        runs under; stored after @name in the same allocation\n  * @name: the name the load program selects it by; empty for the fixed\n@@ -33,6 +35,7 @@ struct user_namespace;\n struct binfmt_misc_interp {\n \tstruct list_head\tlist;\n \tstruct file\t\t*file;\n+\tstruct ucounts\t\t*ucounts;\n \tconst char\t\t*path;\n \tchar\t\t\tname[];\n };\ndiff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h\nindex 9c3be157397e0..e38d9e60569f0 100644\n--- a/include/linux/user_namespace.h\n+++ b/include/linux/user_namespace.h\n@@ -57,6 +57,9 @@ enum ucount_type {\n #ifdef CONFIG_FANOTIFY\n \tUCOUNT_FANOTIFY_GROUPS,\n \tUCOUNT_FANOTIFY_MARKS,\n+#endif\n+#if IS_ENABLED(CONFIG_BINFMT_MISC)\n+\tUCOUNT_BINFMT_MISC_INTERPRETERS,\n #endif\n \tUCOUNT_COUNTS,\n };\ndiff --git a/kernel/ucount.c b/kernel/ucount.c\nindex d6dc3e859f129..ec8b1445e2877 100644\n--- a/kernel/ucount.c\n+++ b/kernel/ucount.c\n@@ -4,6 +4,7 @@\n #include \u003clinux/sysctl.h\u003e\n #include \u003clinux/slab.h\u003e\n #include \u003clinux/cred.h\u003e\n+#include \u003clinux/export.h\u003e\n #include \u003clinux/hash.h\u003e\n #include \u003clinux/kmemleak.h\u003e\n #include \u003clinux/user_namespace.h\u003e\n@@ -89,6 +90,9 @@ static const struct ctl_table user_table[] = {\n \tUCOUNT_ENTRY(\"max_fanotify_groups\"),\n \tUCOUNT_ENTRY(\"max_fanotify_marks\"),\n #endif\n+#if IS_ENABLED(CONFIG_BINFMT_MISC)\n+\tUCOUNT_ENTRY(\"max_binfmt_misc_interpreters\"),\n+#endif\n };\n #endif /* CONFIG_SYSCTL */\n \n@@ -233,6 +237,7 @@ struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid,\n \tput_ucounts(ucounts);\n \treturn NULL;\n }\n+EXPORT_SYMBOL_FOR_MODULES(inc_ucount, \"binfmt_misc\");\n \n void dec_ucount(struct ucounts *ucounts, enum ucount_type type)\n {\n@@ -243,6 +248,7 @@ void dec_ucount(struct ucounts *ucounts, enum ucount_type type)\n \t}\n \tput_ucounts(ucounts);\n }\n+EXPORT_SYMBOL_FOR_MODULES(dec_ucount, \"binfmt_misc\");\n \n long inc_rlimit_ucounts(struct ucounts *ucounts, enum rlimit_type type, long v)\n {\ndiff --git a/tools/testing/selftests/exec/.gitignore b/tools/testing/selftests/exec/.gitignore\nindex fbbb1600ddb94..e42ecd4c908d1 100644\n--- a/tools/testing/selftests/exec/.gitignore\n+++ b/tools/testing/selftests/exec/.gitignore\n@@ -20,6 +20,7 @@ xxxxxxxx*\n pipe\n S_I*.test\n binfmt_misc_bpf\n+binfmt_misc_interplimit\n binfmt_bpf_interp\n binfmt_bpf_app\n binfmt_misc_transparent\ndiff --git a/tools/testing/selftests/exec/Makefile b/tools/testing/selftests/exec/Makefile\nindex 410c93606a0c3..b640af8f02b51 100644\n--- a/tools/testing/selftests/exec/Makefile\n+++ b/tools/testing/selftests/exec/Makefile\n@@ -25,6 +25,10 @@ TEST_GEN_PROGS += check-exec\n # or an 'F' entry can pin the instance that owns it. Unprivileged, no bpf.\n TEST_GEN_PROGS += binfmt_misc_selfpin\n \n+# The interpreters an 'F' or 'B' entry pre-opens are charged against\n+# UCOUNT_BINFMT_MISC_INTERPRETERS. Unprivileged, no bpf.\n+TEST_GEN_PROGS += binfmt_misc_interplimit\n+\n # 'D' (register disabled) binfmt_misc test: an entry that exists but does\n # not dispatch until it is enabled. Static magic entry, no bpf toolchain.\n TEST_GEN_PROGS += binfmt_misc_disabled\n@@ -104,6 +108,8 @@ $(OUTPUT)/script-noexec.inc: $(CHECK_EXEC_SAMPLES)/script-noexec.inc\n # CFLAGS for every program in this directory.\n $(OUTPUT)/binfmt_misc_selfpin: CFLAGS += $(TOOLS_INCLUDES)\n $(OUTPUT)/binfmt_misc_selfpin: ../filesystems/utils.c\n+$(OUTPUT)/binfmt_misc_interplimit: CFLAGS += $(TOOLS_INCLUDES)\n+$(OUTPUT)/binfmt_misc_interplimit: ../filesystems/utils.c\n \n # --- binfmt_misc bpf ('B') handler test ---------------------------------\n # The struct_ops bpf objects are compiled against the running kernel's BTF.\ndiff --git a/tools/testing/selftests/exec/binfmt_misc_bpf.c b/tools/testing/selftests/exec/binfmt_misc_bpf.c\nindex 2c7b63075f1d9..b2a4518901b0f 100644\n--- a/tools/testing/selftests/exec/binfmt_misc_bpf.c\n+++ b/tools/testing/selftests/exec/binfmt_misc_bpf.c\n@@ -38,6 +38,7 @@\n #define _GNU_SOURCE\n #include \u003celf.h\u003e\n #include \u003climits.h\u003e\n+#include \u003csched.h\u003e\n #include \u003cstdio.h\u003e\n #include \u003cstdlib.h\u003e\n #include \u003cstring.h\u003e\n@@ -65,6 +66,9 @@\n #define BIND_RISCV_PATH\t\"/tmp/binfmt_bind_riscv\"\n #define BIND_EXPECT\t\"BIND_RAN \"\n #define BIND_MAX\t100\n+#define INTERP_LIMIT\t\"/proc/sys/user/max_binfmt_misc_interpreters\"\n+/* Exit status of the binding child when it cannot set up a budget of its own. */\n+#define BIND_NO_BUDGET\t200\n \n /* A minimal 64-bit little-endian ELF header, padded to the read size. */\n static int create_fake_elf(const char *path, unsigned short machine)\n@@ -378,6 +382,57 @@ static int entry_bind(const char *entry, const char *name, const char *path)\n \treturn entry_command(entry, cmd);\n }\n \n+/* Set the interpreter budget of this namespace. */\n+static int write_interp_limit(const char *val)\n+{\n+\tssize_t n;\n+\tint fd;\n+\n+\tfd = open(INTERP_LIMIT, O_WRONLY | O_CLOEXEC);\n+\tif (fd \u003c 0)\n+\t\treturn -1;\n+\tn = write(fd, val, strlen(val));\n+\tclose(fd);\n+\treturn n \u003c 0 ? -1 : 0;\n+}\n+\n+/*\n+ * The errno a bind is refused with when the writer is a child that has spent\n+ * the budget of a user namespace of its own, 0 if it succeeded and -1 if the\n+ * child could not set itself up. The fd is opened here and inherited, so the\n+ * interpreter is still opened with this process's credentials.\n+ */\n+static int bind_out_of_budget(const char *entry, const char *name,\n+\t\t\t      const char *path)\n+{\n+\tchar cmd[PATH_MAX], file[PATH_MAX];\n+\tint fd, status, retval;\n+\tpid_t pid;\n+\n+\tsnprintf(file, sizeof(file), BINFMT_DIR \"/%s\", entry);\n+\tsnprintf(cmd, sizeof(cmd), \"+%s %s\\n\", name, path);\n+\n+\tfd = open(file, O_WRONLY | O_CLOEXEC);\n+\tif (fd \u003c 0)\n+\t\treturn -1;\n+\n+\tpid = fork();\n+\tif (pid == 0) {\n+\t\tssize_t n;\n+\n+\t\t/* A namespace of its own, with nothing left in it to spend. */\n+\t\tif (unshare(CLONE_NEWUSER) || write_interp_limit(\"0\"))\n+\t\t\t_exit(BIND_NO_BUDGET);\n+\t\tn = write(fd, cmd, strlen(cmd));\n+\t\t_exit(n \u003c 0 ? errno : 0);\n+\t}\n+\tclose(fd);\n+\tif (pid \u003c 0 || waitpid(pid, \u0026status, 0) != pid || !WIFEXITED(status))\n+\t\treturn -1;\n+\tretval = WEXITSTATUS(status);\n+\treturn retval == BIND_NO_BUDGET ? -1 : retval;\n+}\n+\n FIXTURE(bound_interp) {\n \tchar obj[PATH_MAX];\n \tstruct bpf_case c;\n@@ -565,4 +620,19 @@ TEST_F(bound_interp, capped_bindings)\n \tEXPECT_EQ(entry_bind(\"test_interp_bind\", \"over\", BIND_FIRST), -ENOSPC);\n }\n \n+/* A binding pins a file: it is charged, and refused once the budget is out. */\n+TEST_F(bound_interp, bindings_are_charged)\n+{\n+\tint err = bind_out_of_budget(\"test_interp_bind\", \"third\", BIND_FIRST);\n+\n+\tif (err \u003c 0)\n+\t\tSKIP(return, \"no user namespaces or no \" INTERP_LIMIT);\n+\n+\t/* The charge follows the writer, not the entry file it writes to. */\n+\tEXPECT_EQ(err, ENOSPC);\n+\n+\t/* The budget was the only thing in the way. */\n+\tEXPECT_EQ(entry_bind(\"test_interp_bind\", \"third\", BIND_FIRST), 0);\n+}\n+\n TEST_HARNESS_MAIN\ndiff --git a/tools/testing/selftests/exec/binfmt_misc_interplimit.c b/tools/testing/selftests/exec/binfmt_misc_interplimit.c\nnew file mode 100644\nindex 0000000000000..bf611c5517842\n--- /dev/null\n+++ b/tools/testing/selftests/exec/binfmt_misc_interplimit.c\n@@ -0,0 +1,232 @@\n+// SPDX-License-Identifier: GPL-2.0\n+/*\n+ * A pre-opened interpreter - what 'F' gives a static entry and what a 'B'\n+ * entry binds - keeps a file open for as long as the entry lives, so it pins\n+ * the mount it came from. It costs no file descriptor, and binfmt_misc is\n+ * FS_USERNS_MOUNT, so an unprivileged user namespace can create them without\n+ * bound. Check that UCOUNT_BINFMT_MISC_INTERPRETERS bounds it, that an entry\n+ * that pre-opens nothing is not charged, that removing an entry gives the\n+ * charge back, and that nesting a user namespace does not evade it.\n+ *\n+ * Runs unprivileged in a user namespace.\n+ */\n+#define _GNU_SOURCE\n+#include \u003cerrno.h\u003e\n+#include \u003cfcntl.h\u003e\n+#include \u003climits.h\u003e\n+#include \u003cstdio.h\u003e\n+#include \u003cstring.h\u003e\n+#include \u003csys/mount.h\u003e\n+#include \u003csys/stat.h\u003e\n+#include \u003cunistd.h\u003e\n+\n+#include \"../filesystems/utils.h\"\n+#include \"kselftest_harness.h\"\n+\n+#define MNT\t\t\"/tmp/binfmt_interplimit\"\n+#define NESTED_MNT\t\"/tmp/binfmt_interplimit_nested\"\n+#define LIMIT_SYSCTL\t\"/proc/sys/user/max_binfmt_misc_interpreters\"\n+\n+#define MAGIC\t\t\"\\\\xde\\\\xad\"\n+/* Not on the instance, and unlike /bin/true it always exists. */\n+#define INTERP\t\t\"/proc/self/exe\"\n+\n+/* Small enough to fill by hand, big enough that a refund is visible. */\n+#define LIMIT\t\t4\n+\n+/* What UCOUNT_ENTRY() lets a namespace raise its own limit to. */\n+#define LIMIT_MAX\t\"2147483647\"\n+\n+static int ensure_dir(const char *path)\n+{\n+\tif (mkdir(path, 0755) \u0026\u0026 errno != EEXIST)\n+\t\treturn -1;\n+\treturn 0;\n+}\n+\n+/* Write @val to @path, preserving write(2)'s errno for the caller. */\n+static int write_keep_errno(const char *path, const char *val)\n+{\n+\tint fd, saved;\n+\tssize_t n;\n+\n+\tfd = open(path, O_WRONLY | O_CLOEXEC);\n+\tif (fd \u003c 0)\n+\t\treturn -1;\n+\tn = write(fd, val, strlen(val));\n+\tsaved = errno;\n+\tclose(fd);\n+\terrno = saved;\n+\treturn n \u003c 0 ? -1 : 0;\n+}\n+\n+static int set_limit(const char *val)\n+{\n+\treturn write_keep_errno(LIMIT_SYSCTL, val);\n+}\n+\n+static int register_at(const char *mnt, const char *rule)\n+{\n+\tchar path[PATH_MAX];\n+\n+\tsnprintf(path, sizeof(path), \"%s/register\", mnt);\n+\treturn write_keep_errno(path, rule);\n+}\n+\n+/* An 'F' entry: one interpreter pre-opened at registration, one charge. */\n+static int register_fixed(const char *mnt, const char *name)\n+{\n+\tchar rule[PATH_MAX];\n+\n+\tsnprintf(rule, sizeof(rule), \":%s:M::\" MAGIC \"::\" INTERP \":F\", name);\n+\treturn register_at(mnt, rule);\n+}\n+\n+/* The same entry without 'F': the interpreter is opened per exec instead. */\n+static int register_plain(const char *mnt, const char *name)\n+{\n+\tchar rule[PATH_MAX];\n+\n+\tsnprintf(rule, sizeof(rule), \":%s:M::\" MAGIC \"::\" INTERP \":\", name);\n+\treturn register_at(mnt, rule);\n+}\n+\n+static int remove_entry(const char *mnt, const char *name)\n+{\n+\tchar path[PATH_MAX];\n+\n+\tsnprintf(path, sizeof(path), \"%s/%s\", mnt, name);\n+\treturn write_keep_errno(path, \"-1\\n\");\n+}\n+\n+static bool entry_exists(const char *mnt, const char *name)\n+{\n+\tchar path[PATH_MAX];\n+\n+\tsnprintf(path, sizeof(path), \"%s/%s\", mnt, name);\n+\treturn access(path, F_OK) == 0;\n+}\n+\n+/* Register @n 'F' entries, each with a name of its own. */\n+static int fill_budget(const char *mnt, unsigned int n)\n+{\n+\tchar name[32];\n+\tunsigned int i;\n+\n+\tfor (i = 0; i \u003c n; i++) {\n+\t\tsnprintf(name, sizeof(name), \"fixed%u\", i);\n+\t\tif (register_fixed(mnt, name))\n+\t\t\treturn -1;\n+\t}\n+\treturn 0;\n+}\n+\n+FIXTURE(interp_limit) {\n+};\n+\n+FIXTURE_SETUP(interp_limit)\n+{\n+\t/* setup_userns() exits rather than returns if this is not there. */\n+\tif (access(\"/proc/self/ns/user\", F_OK))\n+\t\tSKIP(return, \"kernel without user namespaces\");\n+\tASSERT_EQ(setup_userns(), 0);\n+\n+\t/* CAP_SYS_RESOURCE in this namespace is what makes it writable. */\n+\tif (set_limit(LIMIT_MAX)) {\n+\t\tif (errno == ENOENT)\n+\t\t\tSKIP(return, \"kernel without \" LIMIT_SYSCTL);\n+\t\tSKIP(return, \"cannot set the limit: %s\", strerror(errno));\n+\t}\n+\n+\tASSERT_EQ(ensure_dir(MNT), 0);\n+\tif (mount(\"binfmt_misc\", MNT, \"binfmt_misc\", 0, NULL)) {\n+\t\tint saved = errno;\n+\n+\t\t/* Teardown doesn't run when setup skips, so clean up here. */\n+\t\trmdir(MNT);\n+\t\tSKIP(return, \"no binfmt_misc: %s\", strerror(saved));\n+\t}\n+}\n+\n+FIXTURE_TEARDOWN(interp_limit)\n+{\n+\t/* The namespaces go with the process; just don't litter /tmp. */\n+\tumount2(NESTED_MNT, MNT_DETACH);\n+\tumount2(MNT, MNT_DETACH);\n+\trmdir(NESTED_MNT);\n+\trmdir(MNT);\n+}\n+\n+/* Every pre-opened interpreter is charged, and the budget is a hard stop. */\n+TEST_F(interp_limit, fixed_interpreters_are_charged)\n+{\n+\tchar buf[32];\n+\n+\tsnprintf(buf, sizeof(buf), \"%u\", LIMIT);\n+\tASSERT_EQ(set_limit(buf), 0);\n+\n+\tASSERT_EQ(fill_budget(MNT, LIMIT), 0);\n+\n+\tEXPECT_NE(register_fixed(MNT, \"over\"), 0);\n+\tEXPECT_EQ(errno, ENOSPC);\n+\n+\t/* A refused registration leaves nothing behind. */\n+\tEXPECT_FALSE(entry_exists(MNT, \"over\"));\n+}\n+\n+/* An entry that pre-opens nothing pins nothing, so it is not charged. */\n+TEST_F(interp_limit, plain_entries_are_not_charged)\n+{\n+\tASSERT_EQ(set_limit(\"0\"), 0);\n+\n+\tEXPECT_EQ(register_plain(MNT, \"plain\"), 0);\n+\tEXPECT_TRUE(entry_exists(MNT, \"plain\"));\n+\n+\t/* ... while the same entry with 'F' has nothing to spend. */\n+\tEXPECT_NE(register_fixed(MNT, \"fixed\"), 0);\n+\tEXPECT_EQ(errno, ENOSPC);\n+}\n+\n+/* Removing an entry closes its interpreters and gives the charge back. */\n+TEST_F(interp_limit, removal_refunds_the_charge)\n+{\n+\tchar buf[32];\n+\n+\tsnprintf(buf, sizeof(buf), \"%u\", LIMIT);\n+\tASSERT_EQ(set_limit(buf), 0);\n+\n+\tASSERT_EQ(fill_budget(MNT, LIMIT), 0);\n+\tASSERT_NE(register_fixed(MNT, \"over\"), 0);\n+\n+\tASSERT_EQ(remove_entry(MNT, \"fixed0\"), 0);\n+\tEXPECT_EQ(register_fixed(MNT, \"over\"), 0);\n+}\n+\n+/*\n+ * The charge walks the ancestors, so a namespace cannot buy itself budget by\n+ * nesting: it may raise only its own limit, and the parent it was created\n+ * from is charged for every binding made below it.\n+ */\n+TEST_F(interp_limit, nesting_does_not_evade_it)\n+{\n+\tchar buf[32];\n+\n+\tsnprintf(buf, sizeof(buf), \"%u\", LIMIT);\n+\tASSERT_EQ(set_limit(buf), 0);\n+\tASSERT_EQ(fill_budget(MNT, LIMIT), 0);\n+\n+\tASSERT_EQ(setup_userns(), 0);\n+\tASSERT_EQ(set_limit(LIMIT_MAX), 0);\n+\n+\tASSERT_EQ(ensure_dir(NESTED_MNT), 0);\n+\tASSERT_EQ(mount(\"binfmt_misc\", NESTED_MNT, \"binfmt_misc\", 0, NULL), 0);\n+\n+\t/* A fresh instance with an unlimited budget of its own, and yet: */\n+\tEXPECT_NE(register_fixed(NESTED_MNT, \"nested\"), 0);\n+\tEXPECT_EQ(errno, ENOSPC);\n+\n+\t/* The nested instance works for anything that pins no file. */\n+\tEXPECT_EQ(register_plain(NESTED_MNT, \"nested_plain\"), 0);\n+}\n+\n+TEST_HARNESS_MAIN\n"
}

best-expensive

null

{
  "EnableConfigs": [
    "BINFMT_MISC",
    "USER_NS"
  ],
  "FocusSymbols": [
    "bm_register_write",
    "bm_entry_write",
    "bm_evict_inode"
  ],
  "Reasoning": "The patch introduces a new sysctl limit `max_binfmt_misc_interpreters` to restrict the number of pre-opened interpreters in `binfmt_misc` using `ucounts`. This is a functional change to the core kernel and `binfmt_misc` filesystem that is reachable from userspace by unprivileged users (in a user namespace). Fuzzing should focus on the registration and removal of `binfmt_misc` entries to test the charging and uncharging of the budget.",
  "WorthFuzzing": true
}

You are an expert Linux kernel maintainer.
Your job is to review a provided patch series and determine
if it makes functional changes to the kernel that should be fuzzed.

IMPORTANT: The changes have ALREADY been applied and committed as the HEAD commit in
your workspace. Do NOT rely on your internal knowledge of the kernel. You must actively
use your code access tools to examine the actual source code and confirm any assumptions.

Return WorthFuzzing=false if the patch only contains:
- Modifications to Documentation/, Kconfig files, or code comments.
- Purely decorative changes, such as logging (e.g., pr_err, printk) or tracepoints.
- Changes to numeric constants or macros that do not functionally alter execution flow.
- Code paths that are impossible to reach in virtualized environments like GCE or QEMU,
  even when utilizing software-emulated hardware (e.g., usb gadget, mac80211_hwsim).
- Code in vendor-specific PCIe switch, SmartNIC, or GPU drivers (e.g., mlxsw, pds_core, qed,
  ionic, amdgpu) that require physical PCIe hardware cards not emulated in standard QEMU.
- Driver .remove, .shutdown, or pci_unregister_driver teardown callbacks (e.g., igb_remove)
  that are executed only during PCI hot-unplug or sysfs driver unbind operations.

If it modifies reachable core kernel logic, drivers, or architectures, use your code search
tools to verify the code can be executed, then return WorthFuzzing=true.

When returning WorthFuzzing=true, you MUST ALSO:
1. Extract any specific kernel functions that should be heavily fuzzed into FocusSymbols.
   Avoid listing generic hot-path functions to prevent skewed test distributions.
   Prefer non-static, non-inlined API entrypoint functions over internal static helper functions
   (which are inlined by the compiler and do not have distinct symbol addresses).
2. Identify any specific CONFIG_ options required to properly test this new/modified feature.
   Go and look into the Kconfig files and check for ifdefs around the code, do not make assumptions.
   Also check "depends on" lines in Kconfig to include any non-standard parent subsystem configs
   needed for Kbuild to compile the code statically into vmlinux. List them in the EnableConfigs
   output array, and DO NOT add a 'CONFIG_' prefix (e.g., return "NET_IPV4" instead of "CONFIG_NET_IPV4").
Prefer calling several tools at the same time to save round-trips.


Use set-results tool to provide results of the analysis.
It must be called exactly once before the final reply.
Ignore results of this tool.

For your convenience, here is the diff of the changes:
commit abe853e3c93c8c19de2ae2375fa767eb5bd35667
Author: syz-cluster <triage@syzkaller.com>
Date:   Mon Aug 3 14:46:47 2026 +0000

    syz-cluster: applied patch under review

diff --git a/Documentation/admin-guide/binfmt-misc.rst b/Documentation/admin-guide/binfmt-misc.rst
index 622b5d8c89957..d26b63a27c259 100644
--- a/Documentation/admin-guide/binfmt-misc.rst
+++ b/Documentation/admin-guide/binfmt-misc.rst
@@ -128,6 +128,11 @@ There are some restrictions:
    named by an absolute path. It is opened when the binary is executed, so
    a relative one would be resolved against the working directory of
    whoever runs the binary
+ - the amount of pre-opened interpreters by ``F``, or bound to a ``B`` entry
+   is limited by the ``/proc/sys/user/max_binfmt_misc_interpreters`` sysctl. A
+   registration past the limit is refused with ``-ENOSPC``. This limits an
+   unprivileged namespace pinning files. A nested namespace can raise only its
+   own limit and every ancestor is charged too
 
 
 To use binfmt_misc you have to mount it first. You can mount it with
@@ -215,10 +220,9 @@ with the credentials the entry file was opened with, exactly the way ``F``
 pre-opens a static entry's interpreter; the paths must be absolute. The
 path is everything past the first space, so there is nothing it cannot
 express, and no interpreter has to fit in a register string. An entry
-binds at most 100 interpreters; a write past that is refused with
-``-ENOSPC``. To bind a file that has no path of its own - already
-unlinked, a ``memfd``, or reachable only in another mount namespace -
-open it and write ``/proc/self/fd/N``.
+binds at most 100 interpreters, and each one is charged against
+``max_binfmt_misc_interpreters`` like any other binding. A write past either
+limit is refused with ``-ENOSPC``.
 
 The ``load`` program then selects one per exec by name with the
 ``bpf_binprm_select_interp()`` kfunc, and every exec runs a clone of the
diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c
index ad8c4f64bf102..a3aa42fd57614 100644
--- a/fs/binfmt_misc.c
+++ b/fs/binfmt_misc.c
@@ -289,6 +289,7 @@ static void entry_put_interpreters(struct binfmt_misc_entry *e)
 	list_for_each_entry_safe(interp, tmp, &e->interps, list) {
 		list_del(&interp->list);
 		close_interp_file(interp->file);
+		dec_ucount(interp->ucounts, UCOUNT_BINFMT_MISC_INTERPRETERS);
 		kfree(interp);
 	}
 }
@@ -307,7 +308,8 @@ static void entry_put_interpreters(struct binfmt_misc_entry *e)
  * The caller has to have validated @name and @path, established that @e
  * cannot be matched yet, and owns @f until this succeeds.
  *
- * Return: 0 on success, a negative errno on failure
+ * Return: 0 on success, -ENOSPC if the entry is full or the binder is out of
+ *         UCOUNT_BINFMT_MISC_INTERPRETERS budget, a negative errno on failure
  */
 static int entry_attach_interpreter(struct binfmt_misc_entry *e,
 				    const char *name, const char *path,
@@ -315,22 +317,32 @@ static int entry_attach_interpreter(struct binfmt_misc_entry *e,
 {
 	size_t nlen = strlen(name), plen = strlen(path);
 	struct binfmt_misc_interp *interp;
+	struct ucounts *ucounts;
 
 	if (binfmt_misc_find_interp(&e->interps, name))
 		return -EEXIST;
 	if (list_count_nodes(&e->interps) >= BINFMT_MISC_INTERP_MAX)
 		return -ENOSPC;
 
+	/* The binding keeps a file open, so charge it to whoever binds it. */
+	ucounts = inc_ucount(current_user_ns(), current_euid(),
+			     UCOUNT_BINFMT_MISC_INTERPRETERS);
+	if (!ucounts)
+		return -ENOSPC;
+
 	/* One allocation, both strings in it, like the entry's own buffer. */
 	interp = kmalloc(struct_size(interp, name, nlen + plen + 2),
 			 GFP_KERNEL_ACCOUNT);
-	if (!interp)
+	if (!interp) {
+		dec_ucount(ucounts, UCOUNT_BINFMT_MISC_INTERPRETERS);
 		return -ENOMEM;
+	}
 
 	interp->path = interp->name + nlen + 1;
 	strscpy(interp->name, name, nlen + 1);
 	strscpy(interp->name + nlen + 1, path, plen + 1);
 	interp->file = f;
+	interp->ucounts = ucounts;
 	/* Publish the node: a lockless cat may be walking the list. */
 	list_add_tail_rcu(&interp->list, &e->interps);
 	pr_debug("register: interpreter: %s {%s}\n", name, path);
diff --git a/include/linux/binfmt_misc.h b/include/linux/binfmt_misc.h
index 072e4b3dd78d2..8045b10dd3e5c 100644
--- a/include/linux/binfmt_misc.h
+++ b/include/linux/binfmt_misc.h
@@ -7,6 +7,7 @@
 struct bpf_prog;
 struct file;
 struct linux_binprm;
+struct ucounts;
 struct user_namespace;
 
 #define BINFMT_MISC_OPS_NAME_MAX 16
@@ -21,6 +22,7 @@ struct user_namespace;
  * struct binfmt_misc_interp - an interpreter an entry was registered with
  * @list: link in the entry's list, in registration order
  * @file: the file, opened at registration and never resolved again
+ * @ucounts: the UCOUNT_BINFMT_MISC_INTERPRETERS charge the binding took
  * @path: the path it was registered under, used as the name the interpreter
  *        runs under; stored after @name in the same allocation
  * @name: the name the load program selects it by; empty for the fixed
@@ -33,6 +35,7 @@ struct user_namespace;
 struct binfmt_misc_interp {
 	struct list_head	list;
 	struct file		*file;
+	struct ucounts		*ucounts;
 	const char		*path;
 	char			name[];
 };
diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index 9c3be157397e0..e38d9e60569f0 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -57,6 +57,9 @@ enum ucount_type {
 #ifdef CONFIG_FANOTIFY
 	UCOUNT_FANOTIFY_GROUPS,
 	UCOUNT_FANOTIFY_MARKS,
+#endif
+#if IS_ENABLED(CONFIG_BINFMT_MISC)
+	UCOUNT_BINFMT_MISC_INTERPRETERS,
 #endif
 	UCOUNT_COUNTS,
 };
diff --git a/kernel/ucount.c b/kernel/ucount.c
index d6dc3e859f129..ec8b1445e2877 100644
--- a/kernel/ucount.c
+++ b/kernel/ucount.c
@@ -4,6 +4,7 @@
 #include <linux/sysctl.h>
 #include <linux/slab.h>
 #include <linux/cred.h>
+#include <linux/export.h>
 #include <linux/hash.h>
 #include <linux/kmemleak.h>
 #include <linux/user_namespace.h>
@@ -89,6 +90,9 @@ static const struct ctl_table user_table[] = {
 	UCOUNT_ENTRY("max_fanotify_groups"),
 	UCOUNT_ENTRY("max_fanotify_marks"),
 #endif
+#if IS_ENABLED(CONFIG_BINFMT_MISC)
+	UCOUNT_ENTRY("max_binfmt_misc_interpreters"),
+#endif
 };
 #endif /* CONFIG_SYSCTL */
 
@@ -233,6 +237,7 @@ struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid,
 	put_ucounts(ucounts);
 	return NULL;
 }
+EXPORT_SYMBOL_FOR_MODULES(inc_ucount, "binfmt_misc");
 
 void dec_ucount(struct ucounts *ucounts, enum ucount_type type)
 {
@@ -243,6 +248,7 @@ void dec_ucount(struct ucounts *ucounts, enum ucount_type type)
 	}
 	put_ucounts(ucounts);
 }
+EXPORT_SYMBOL_FOR_MODULES(dec_ucount, "binfmt_misc");
 
 long inc_rlimit_ucounts(struct ucounts *ucounts, enum rlimit_type type, long v)
 {
diff --git a/tools/testing/selftests/exec/.gitignore b/tools/testing/selftests/exec/.gitignore
index fbbb1600ddb94..e42ecd4c908d1 100644
--- a/tools/testing/selftests/exec/.gitignore
+++ b/tools/testing/selftests/exec/.gitignore
@@ -20,6 +20,7 @@ xxxxxxxx*
 pipe
 S_I*.test
 binfmt_misc_bpf
+binfmt_misc_interplimit
 binfmt_bpf_interp
 binfmt_bpf_app
 binfmt_misc_transparent
diff --git a/tools/testing/selftests/exec/Makefile b/tools/testing/selftests/exec/Makefile
index 410c93606a0c3..b640af8f02b51 100644
--- a/tools/testing/selftests/exec/Makefile
+++ b/tools/testing/selftests/exec/Makefile
@@ -25,6 +25,10 @@ TEST_GEN_PROGS += check-exec
 # or an 'F' entry can pin the instance that owns it. Unprivileged, no bpf.
 TEST_GEN_PROGS += binfmt_misc_selfpin
 
+# The interpreters an 'F' or 'B' entry pre-opens are charged against
+# UCOUNT_BINFMT_MISC_INTERPRETERS. Unprivileged, no bpf.
+TEST_GEN_PROGS += binfmt_misc_interplimit
+
 # 'D' (register disabled) binfmt_misc test: an entry that exists but does
 # not dispatch until it is enabled. Static magic entry, no bpf toolchain.
 TEST_GEN_PROGS += binfmt_misc_disabled
@@ -104,6 +108,8 @@ $(OUTPUT)/script-noexec.inc: $(CHECK_EXEC_SAMPLES)/script-noexec.inc
 # CFLAGS for every program in this directory.
 $(OUTPUT)/binfmt_misc_selfpin: CFLAGS += $(TOOLS_INCLUDES)
 $(OUTPUT)/binfmt_misc_selfpin: ../filesystems/utils.c
+$(OUTPUT)/binfmt_misc_interplimit: CFLAGS += $(TOOLS_INCLUDES)
+$(OUTPUT)/binfmt_misc_interplimit: ../filesystems/utils.c
 
 # --- binfmt_misc bpf ('B') handler test ---------------------------------
 # The struct_ops bpf objects are compiled against the running kernel's BTF.
diff --git a/tools/testing/selftests/exec/binfmt_misc_bpf.c b/tools/testing/selftests/exec/binfmt_misc_bpf.c
index 2c7b63075f1d9..b2a4518901b0f 100644
--- a/tools/testing/selftests/exec/binfmt_misc_bpf.c
+++ b/tools/testing/selftests/exec/binfmt_misc_bpf.c
@@ -38,6 +38,7 @@
 #define _GNU_SOURCE
 #include <elf.h>
 #include <limits.h>
+#include <sched.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -65,6 +66,9 @@
 #define BIND_RISCV_PATH	"/tmp/binfmt_bind_riscv"
 #define BIND_EXPECT	"BIND_RAN "
 #define BIND_MAX	100
+#define INTERP_LIMIT	"/proc/sys/user/max_binfmt_misc_interpreters"
+/* Exit status of the binding child when it cannot set up a budget of its own. */
+#define BIND_NO_BUDGET	200
 
 /* A minimal 64-bit little-endian ELF header, padded to the read size. */
 static int create_fake_elf(const char *path, unsigned short machine)
@@ -378,6 +382,57 @@ static int entry_bind(const char *entry, const char *name, const char *path)
 	return entry_command(entry, cmd);
 }
 
+/* Set the interpreter budget of this namespace. */
+static int write_interp_limit(const char *val)
+{
+	ssize_t n;
+	int fd;
+
+	fd = open(INTERP_LIMIT, O_WRONLY | O_CLOEXEC);
+	if (fd < 0)
+		return -1;
+	n = write(fd, val, strlen(val));
+	close(fd);
+	return n < 0 ? -1 : 0;
+}
+
+/*
+ * The errno a bind is refused with when the writer is a child that has spent
+ * the budget of a user namespace of its own, 0 if it succeeded and -1 if the
+ * child could not set itself up. The fd is opened here and inherited, so the
+ * interpreter is still opened with this process's credentials.
+ */
+static int bind_out_of_budget(const char *entry, const char *name,
+			      const char *path)
+{
+	char cmd[PATH_MAX], file[PATH_MAX];
+	int fd, status, retval;
+	pid_t pid;
+
+	snprintf(file, sizeof(file), BINFMT_DIR "/%s", entry);
+	snprintf(cmd, sizeof(cmd), "+%s %s\n", name, path);
+
+	fd = open(file, O_WRONLY | O_CLOEXEC);
+	if (fd < 0)
+		return -1;
+
+	pid = fork();
+	if (pid == 0) {
+		ssize_t n;
+
+		/* A namespace of its own, with nothing left in it to spend. */
+		if (unshare(CLONE_NEWUSER) || write_interp_limit("0"))
+			_exit(BIND_NO_BUDGET);
+		n = write(fd, cmd, strlen(cmd));
+		_exit(n < 0 ? errno : 0);
+	}
+	close(fd);
+	if (pid < 0 || waitpid(pid, &status, 0) != pid || !WIFEXITED(status))
+		return -1;
+	retval = WEXITSTATUS(status);
+	return retval == BIND_NO_BUDGET ? -1 : retval;
+}
+
 FIXTURE(bound_interp) {
 	char obj[PATH_MAX];
 	struct bpf_case c;
@@ -565,4 +620,19 @@ TEST_F(bound_interp, capped_bindings)
 	EXPECT_EQ(entry_bind("test_interp_bind", "over", BIND_FIRST), -ENOSPC);
 }
 
+/* A binding pins a file: it is charged, and refused once the budget is out. */
+TEST_F(bound_interp, bindings_are_charged)
+{
+	int err = bind_out_of_budget("test_interp_bind", "third", BIND_FIRST);
+
+	if (err < 0)
+		SKIP(return, "no user namespaces or no " INTERP_LIMIT);
+
+	/* The charge follows the writer, not the entry file it writes to. */
+	EXPECT_EQ(err, ENOSPC);
+
+	/* The budget was the only thing in the way. */
+	EXPECT_EQ(entry_bind("test_interp_bind", "third", BIND_FIRST), 0);
+}
+
 TEST_HARNESS_MAIN
diff --git a/tools/testing/selftests/exec/binfmt_misc_interplimit.c b/tools/testing/selftests/exec/binfmt_misc_interplimit.c
new file mode 100644
index 0000000000000..bf611c5517842
--- /dev/null
+++ b/tools/testing/selftests/exec/binfmt_misc_interplimit.c
@@ -0,0 +1,232 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * A pre-opened interpreter - what 'F' gives a static entry and what a 'B'
+ * entry binds - keeps a file open for as long as the entry lives, so it pins
+ * the mount it came from. It costs no file descriptor, and binfmt_misc is
+ * FS_USERNS_MOUNT, so an unprivileged user namespace can create them without
+ * bound. Check that UCOUNT_BINFMT_MISC_INTERPRETERS bounds it, that an entry
+ * that pre-opens nothing is not charged, that removing an entry gives the
+ * charge back, and that nesting a user namespace does not evade it.
+ *
+ * Runs unprivileged in a user namespace.
+ */
+#define _GNU_SOURCE
+#include <errno.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/mount.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+#include "../filesystems/utils.h"
+#include "kselftest_harness.h"
+
+#define MNT		"/tmp/binfmt_interplimit"
+#define NESTED_MNT	"/tmp/binfmt_interplimit_nested"
+#define LIMIT_SYSCTL	"/proc/sys/user/max_binfmt_misc_interpreters"
+
+#define MAGIC		"\\xde\\xad"
+/* Not on the instance, and unlike /bin/true it always exists. */
+#define INTERP		"/proc/self/exe"
+
+/* Small enough to fill by hand, big enough that a refund is visible. */
+#define LIMIT		4
+
+/* What UCOUNT_ENTRY() lets a namespace raise its own limit to. */
+#define LIMIT_MAX	"2147483647"
+
+static int ensure_dir(const char *path)
+{
+	if (mkdir(path, 0755) && errno != EEXIST)
+		return -1;
+	return 0;
+}
+
+/* Write @val to @path, preserving write(2)'s errno for the caller. */
+static int write_keep_errno(const char *path, const char *val)
+{
+	int fd, saved;
+	ssize_t n;
+
+	fd = open(path, O_WRONLY | O_CLOEXEC);
+	if (fd < 0)
+		return -1;
+	n = write(fd, val, strlen(val));
+	saved = errno;
+	close(fd);
+	errno = saved;
+	return n < 0 ? -1 : 0;
+}
+
+static int set_limit(const char *val)
+{
+	return write_keep_errno(LIMIT_SYSCTL, val);
+}
+
+static int register_at(const char *mnt, const char *rule)
+{
+	char path[PATH_MAX];
+
+	snprintf(path, sizeof(path), "%s/register", mnt);
+	return write_keep_errno(path, rule);
+}
+
+/* An 'F' entry: one interpreter pre-opened at registration, one charge. */
+static int register_fixed(const char *mnt, const char *name)
+{
+	char rule[PATH_MAX];
+
+	snprintf(rule, sizeof(rule), ":%s:M::" MAGIC "::" INTERP ":F", name);
+	return register_at(mnt, rule);
+}
+
+/* The same entry without 'F': the interpreter is opened per exec instead. */
+static int register_plain(const char *mnt, const char *name)
+{
+	char rule[PATH_MAX];
+
+	snprintf(rule, sizeof(rule), ":%s:M::" MAGIC "::" INTERP ":", name);
+	return register_at(mnt, rule);
+}
+
+static int remove_entry(const char *mnt, const char *name)
+{
+	char path[PATH_MAX];
+
+	snprintf(path, sizeof(path), "%s/%s", mnt, name);
+	return write_keep_errno(path, "-1\n");
+}
+
+static bool entry_exists(const char *mnt, const char *name)
+{
+	char path[PATH_MAX];
+
+	snprintf(path, sizeof(path), "%s/%s", mnt, name);
+	return access(path, F_OK) == 0;
+}
+
+/* Register @n 'F' entries, each with a name of its own. */
+static int fill_budget(const char *mnt, unsigned int n)
+{
+	char name[32];
+	unsigned int i;
+
+	for (i = 0; i < n; i++) {
+		snprintf(name, sizeof(name), "fixed%u", i);
+		if (register_fixed(mnt, name))
+			return -1;
+	}
+	return 0;
+}
+
+FIXTURE(interp_limit) {
+};
+
+FIXTURE_SETUP(interp_limit)
+{
+	/* setup_userns() exits rather than returns if this is not there. */
+	if (access("/proc/self/ns/user", F_OK))
+		SKIP(return, "kernel without user namespaces");
+	ASSERT_EQ(setup_userns(), 0);
+
+	/* CAP_SYS_RESOURCE in this namespace is what makes it writable. */
+	if (set_limit(LIMIT_MAX)) {
+		if (errno == ENOENT)
+			SKIP(return, "kernel without " LIMIT_SYSCTL);
+		SKIP(return, "cannot set the limit: %s", strerror(errno));
+	}
+
+	ASSERT_EQ(ensure_dir(MNT), 0);
+	if (mount("binfmt_misc", MNT, "binfmt_misc", 0, NULL)) {
+		int saved = errno;
+
+		/* Teardown doesn't run when setup skips, so clean up here. */
+		rmdir(MNT);
+		SKIP(return, "no binfmt_misc: %s", strerror(saved));
+	}
+}
+
+FIXTURE_TEARDOWN(interp_limit)
+{
+	/* The namespaces go with the process; just don't litter /tmp. */
+	umount2(NESTED_MNT, MNT_DETACH);
+	umount2(MNT, MNT_DETACH);
+	rmdir(NESTED_MNT);
+	rmdir(MNT);
+}
+
+/* Every pre-opened interpreter is charged, and the budget is a hard stop. */
+TEST_F(interp_limit, fixed_interpreters_are_charged)
+{
+	char buf[32];
+
+	snprintf(buf, sizeof(buf), "%u", LIMIT);
+	ASSERT_EQ(set_limit(buf), 0);
+
+	ASSERT_EQ(fill_budget(MNT, LIMIT), 0);
+
+	EXPECT_NE(register_fixed(MNT, "over"), 0);
+	EXPECT_EQ(errno, ENOSPC);
+
+	/* A refused registration leaves nothing behind. */
+	EXPECT_FALSE(entry_exists(MNT, "over"));
+}
+
+/* An entry that pre-opens nothing pins nothing, so it is not charged. */
+TEST_F(interp_limit, plain_entries_are_not_charged)
+{
+	ASSERT_EQ(set_limit("0"), 0);
+
+	EXPECT_EQ(register_plain(MNT, "plain"), 0);
+	EXPECT_TRUE(entry_exists(MNT, "plain"));
+
+	/* ... while the same entry with 'F' has nothing to spend. */
+	EXPECT_NE(register_fixed(MNT, "fixed"), 0);
+	EXPECT_EQ(errno, ENOSPC);
+}
+
+/* Removing an entry closes its interpreters and gives the charge back. */
+TEST_F(interp_limit, removal_refunds_the_charge)
+{
+	char buf[32];
+
+	snprintf(buf, sizeof(buf), "%u", LIMIT);
+	ASSERT_EQ(set_limit(buf), 0);
+
+	ASSERT_EQ(fill_budget(MNT, LIMIT), 0);
+	ASSERT_NE(register_fixed(MNT, "over"), 0);
+
+	ASSERT_EQ(remove_entry(MNT, "fixed0"), 0);
+	EXPECT_EQ(register_fixed(MNT, "over"), 0);
+}
+
+/*
+ * The charge walks the ancestors, so a namespace cannot buy itself budget by
+ * nesting: it may raise only its own limit, and the parent it was created
+ * from is charged for every binding made below it.
+ */
+TEST_F(interp_limit, nesting_does_not_evade_it)
+{
+	char buf[32];
+
+	snprintf(buf, sizeof(buf), "%u", LIMIT);
+	ASSERT_EQ(set_limit(buf), 0);
+	ASSERT_EQ(fill_budget(MNT, LIMIT), 0);
+
+	ASSERT_EQ(setup_userns(), 0);
+	ASSERT_EQ(set_limit(LIMIT_MAX), 0);
+
+	ASSERT_EQ(ensure_dir(NESTED_MNT), 0);
+	ASSERT_EQ(mount("binfmt_misc", NESTED_MNT, "binfmt_misc", 0, NULL), 0);
+
+	/* A fresh instance with an unlimited budget of its own, and yet: */
+	EXPECT_NE(register_fixed(NESTED_MNT, "nested"), 0);
+	EXPECT_EQ(errno, ENOSPC);
+
+	/* The nested instance works for anything that pins no file. */
+	EXPECT_EQ(register_plain(NESTED_MNT, "nested_plain"), 0);
+}
+
+TEST_HARNESS_MAIN

gemini-3.1-pro-preview

null

null

							input: 8829
							output: 33
							thoughts: 258
						

**My Initial Assessment of the Binfmt_misc Interpreter Limit Patch**

Okay, so I've got this patch here. It's touching `fs/binfmt_misc.c` and adding a new sysctl, `max_binfmt_misc_interpreters`, which is intriguing. Limiting the number of pre-opened interpreters within `binfmt_misc` is a good idea in terms of resource management and potential security hardening. Looks like they're using `inc_ucount` and `dec_ucount` with `UCOUNT_BINFMT_MISC_INTERPRETERS` to manage the accounting, which is the right approach for resource limiting. The changes focus on modifying `entry_attach_interpreter` to apply the charge, and `entry_put_interpreters` to uncharge. They've also added a test, `binfmt_misc_interplimit.c`, and touched `binfmt_misc_bpf.c`.

My first instinct is to dive into `fs/binfmt_misc.c` and `kernel/ucount.c` to see how the limit is implemented. I can immediately see the potential here for fuzzing. `binfmt_misc` is, after all, user-reachable through mounting and writing to the file system. That means any flaw in the logic is potentially exploitable. This is definitely worth a close look.

Now, let's identify the core function to focus on. `entry_attach_interpreter` sounds like the critical point. It's a static function, so I'll need to trace its call sites to understand where it's being used and how it interacts with the rest of the system.

{
  "Expression": "entry_attach_interpreter",
  "PathPrefix": "fs/binfmt_misc.c"
}

{
  "Output": "fs/binfmt_misc.c=285=static void entry_put_interpreters(struct binfmt_misc_entry *e)\n--\nfs/binfmt_misc.c-297-/**\nfs/binfmt_misc.c:298: * entry_attach_interpreter - bind an opened interpreter to @e\nfs/binfmt_misc.c-299- * @e: entry being configured\n--\nfs/binfmt_misc.c-313- */\nfs/binfmt_misc.c:314:static int entry_attach_interpreter(struct binfmt_misc_entry *e,\nfs/binfmt_misc.c-315-\t\t\t\t    const char *name, const char *path,\n--\nfs/binfmt_misc.c=1301=static ssize_t bm_entry_add_interp(struct binfmt_misc_entry *e,\n--\nfs/binfmt_misc.c-1351-\telse\nfs/binfmt_misc.c:1352:\t\tretval = entry_attach_interpreter(e, name, path, f);\nfs/binfmt_misc.c-1353-\tinode_unlock(root);\n--\nfs/binfmt_misc.c=1462=static ssize_t bm_register_write(struct file *file, const char __user *buffer,\n--\nfs/binfmt_misc.c-1486-\t\t\treturn PTR_ERR(f);\nfs/binfmt_misc.c:1487:\t\terr = entry_attach_interpreter(e, \"\", e-\u003einterpreter, f);\nfs/binfmt_misc.c-1488-\t\tif (err) {\n"
}

gemini-3.1-pro-preview

null

null

							input: 9898
							output: 36
							thoughts: 36
						

Okay, here's my take on those thoughts, framed as an expert's internal monologue:

**Investigating Interpreter Attachment**

Right, let's see. I'm looking at how interpreters are being linked within the system. The code's calling `bm_entry_add_interp` and `bm_register_write`, and both of those ultimately go through `entry_attach_interpreter`. My immediate concern is scoping – specifically, are these functions, the ones doing the attaching, declared as static? That's the crucial question. If they *are* static, it really limits the potential for external manipulation or unintended side effects in other parts of the system. I need to confirm whether their visibility is restricted to the current compilation unit, or if they are globally accessible. This has implications for security, maintainability, and understanding the overall architectural design. I'll need to trace those declarations quickly to get a handle on the exposure.

{
  "Expression": "bm_entry_add_interp",
  "PathPrefix": "fs/binfmt_misc.c"
}

{
  "Output": "fs/binfmt_misc.c=1264=static int bm_entry_open(struct inode *inode, struct file *file)\n--\nfs/binfmt_misc.c-1285-/**\nfs/binfmt_misc.c:1286: * bm_entry_add_interp - bind another interpreter to a staged entry\nfs/binfmt_misc.c-1287- * @e: the entry\n--\nfs/binfmt_misc.c-1300- */\nfs/binfmt_misc.c:1301:static ssize_t bm_entry_add_interp(struct binfmt_misc_entry *e,\nfs/binfmt_misc.c-1302-\t\t\t\t   struct file *file, char *buf, size_t count)\n--\nfs/binfmt_misc.c=1362=static ssize_t bm_entry_write(struct file *file, const char __user *buffer,\n--\nfs/binfmt_misc.c-1379-\tif (buf[0] == '+')\nfs/binfmt_misc.c:1380:\t\treturn bm_entry_add_interp(e, file, buf, count);\nfs/binfmt_misc.c-1381-\n"
}

gemini-3.1-pro-preview

null

null

							input: 10486
							output: 33
							thoughts: 26
						

Okay, here's my take on those thoughts, framed for an expert like yourself:

**Diving into the Write Operation**

Alright, so we're talking about `bm_entry_write`. That tells me we're looking at the file operation write function, specifically within the Block Manager. My initial focus is on confirming how writes are registered. Let's dig into `bm_register_write` to see how it's handled internally. We need to understand the relationship between registering a write and the underlying mechanics.

{
  "Expression": "bm_register_write",
  "PathPrefix": "fs/binfmt_misc.c"
}

{
  "Output": "fs/binfmt_misc.c=1431=static int add_entry(struct binfmt_misc_entry *e, struct super_block *sb)\n--\nfs/binfmt_misc.c-1461-\nfs/binfmt_misc.c:1462:static ssize_t bm_register_write(struct file *file, const char __user *buffer,\nfs/binfmt_misc.c-1463-\t\t\t       size_t count, loff_t *ppos)\n--\nfs/binfmt_misc.c=1503=static const struct file_operations bm_register_operations = {\nfs/binfmt_misc.c:1504:\t.write\t\t= bm_register_write,\nfs/binfmt_misc.c-1505-\t.llseek\t\t= noop_llseek,\n"
}

gemini-3.1-pro-preview

null

null

							input: 10874
							output: 33
							thoughts: 34
						

Okay, here's my take on those functions.

**Initial Assessment of Entry Points**

Alright, let's zoom in on this code. It looks like `bm_register_write` and `bm_entry_write` are the primary entry points for whatever this system is doing. Given their names, I'm guessing one handles register-level writes and the other manages data entries. Seems logical, a standard architectural breakdown, and likely follows a common software design pattern. To understand the overall functionality, my immediate focus has to be on `bm_entry_write`. I need to figure out how it operates, that will likely illuminate the whole operation. Let's dig in.

{
  "Expression": "bm_entry_write",
  "PathPrefix": "fs/binfmt_misc.c"
}

{
  "Output": "fs/binfmt_misc.c=1264=static int bm_entry_open(struct inode *inode, struct file *file)\n--\nfs/binfmt_misc.c-1271-\nfs/binfmt_misc.c:1272:\t/* seq_open() clears FMODE_PWRITE, bm_entry_write() takes any offset */\nfs/binfmt_misc.c-1273-\tif (file-\u003ef_mode \u0026 FMODE_WRITE)\n--\nfs/binfmt_misc.c=1301=static ssize_t bm_entry_add_interp(struct binfmt_misc_entry *e,\n--\nfs/binfmt_misc.c-1361-\nfs/binfmt_misc.c:1362:static ssize_t bm_entry_write(struct file *file, const char __user *buffer,\nfs/binfmt_misc.c-1363-\t\t\t\tsize_t count, loff_t *ppos)\n--\nfs/binfmt_misc.c=1420=static const struct file_operations bm_entry_operations = {\n--\nfs/binfmt_misc.c-1422-\t.read\t\t= seq_read,\nfs/binfmt_misc.c:1423:\t.write\t\t= bm_entry_write,\nfs/binfmt_misc.c-1424-\t.llseek\t\t= seq_lseek,\n"
}

gemini-3.1-pro-preview

null

null

							input: 11445
							output: 34
							thoughts: 20
						

Okay, here's my summary, presented as a stream of thought:

**Checking for Complete File Operation Coverage**

Alright, I'm thinking, "Have we truly accounted for *all* the file operations here?" It's a critical question to ask, especially when dealing with potentially complex data manipulation. My next step? I need to quickly and comprehensively scan our current implementations to see if we've missed anything. My instinct is to zero in on areas where we put information into a system, which should cover the most important aspects. "Let's check `entry_put_interpreters`". I'll use that as a jumping-off point to make sure we've captured the core actions properly.

{
  "Expression": "entry_put_interpreters",
  "PathPrefix": "fs/binfmt_misc.c"
}

{
  "Output": "fs/binfmt_misc.c=273=static struct file *open_interp_file(const struct cred *cred, const char *path)\n--\nfs/binfmt_misc.c-284-/* Release the interpreters an entry was registered with. */\nfs/binfmt_misc.c:285:static void entry_put_interpreters(struct binfmt_misc_entry *e)\nfs/binfmt_misc.c-286-{\n--\nfs/binfmt_misc.c=371=static void put_binfmt_handler(struct binfmt_misc_entry *e)\n--\nfs/binfmt_misc.c-376-\tif (refcount_dec_and_test(\u0026e-\u003eusers)) {\nfs/binfmt_misc.c:377:\t\tentry_put_interpreters(e);\nfs/binfmt_misc.c-378-\t\t/* Walkers may still dereference this entry, even sleeping. */\n"
}

gemini-3.1-pro-preview

null

null

							input: 11893
							output: 34
							thoughts: 29
						

Here's my summary, as though I'm thinking through this process:

**Diving into binfmt_handler Removal**

Okay, so I'm focusing on the `put_binfmt_handler` function. The key here is that it's triggered during the *removal* of a binfmt handler. That makes immediate sense; we need a mechanism to gracefully clean up after a handler is no longer active. Let's see what happens within that function, exactly. What cleanup tasks are initiated? What resources are freed? I expect a well-designed handler will have allocated some kernel structures and perhaps file descriptors, so I want to understand how memory is freed and if we are calling appropriate destruction functions for that data. This is crucial for stability and resource management in the kernel. Let's dig in and examine the implementation of `put_binfmt_handler` directly.

{
  "Expression": "put_binfmt_handler",
  "PathPrefix": "fs/binfmt_misc.c"
}

{
  "Output": "fs/binfmt_misc.c=352=static void bm_entry_free_rcu(struct rcu_head *rcu)\n--\nfs/binfmt_misc.c-362-/**\nfs/binfmt_misc.c:363: * put_binfmt_handler - put binary handler entry\nfs/binfmt_misc.c-364- * @e: entry to put\n--\nfs/binfmt_misc.c-370- */\nfs/binfmt_misc.c:371:static void put_binfmt_handler(struct binfmt_misc_entry *e)\nfs/binfmt_misc.c-372-{\n--\nfs/binfmt_misc.c-382-\nfs/binfmt_misc.c:383:DEFINE_FREE(put_binfmt_handler, struct binfmt_misc_entry *, put_binfmt_handler(_T))\nfs/binfmt_misc.c-384-\n--\nfs/binfmt_misc.c=621=static int load_misc_binary(struct linux_binprm *bprm)\nfs/binfmt_misc.c-622-{\nfs/binfmt_misc.c:623:\tstruct binfmt_misc_entry *fmt __free(put_binfmt_handler) = NULL;\nfs/binfmt_misc.c-624-\tconst char *interpreter;\n--\nfs/binfmt_misc.c=848=static struct binfmt_misc_entry *create_entry(const char __user *buffer,\n--\nfs/binfmt_misc.c-994-\nfs/binfmt_misc.c:995:\t/* Born holding one reference; put_binfmt_handler() is the teardown. */\nfs/binfmt_misc.c-996-\trefcount_set(\u0026e-\u003eusers, 1);\n--\nfs/binfmt_misc.c=1149=static void bm_evict_inode(struct inode *inode)\n--\nfs/binfmt_misc.c-1162-\t\tspin_unlock(\u0026misc-\u003eentries_lock);\nfs/binfmt_misc.c:1163:\t\tput_binfmt_handler(e);\nfs/binfmt_misc.c-1164-\t}\n--\nfs/binfmt_misc.c=1462=static ssize_t bm_register_write(struct file *file, const char __user *buffer,\n--\nfs/binfmt_misc.c-1464-{\nfs/binfmt_misc.c:1465:\tstruct binfmt_misc_entry *e __free(put_binfmt_handler) = NULL;\nfs/binfmt_misc.c-1466-\tstruct super_block *sb = file_inode(file)-\u003ei_sb;\n"
}

gemini-3.1-pro-preview

null

null

							input: 12838
							output: 34
							thoughts: 138
						

**Analyzing the binfmt_misc Interpreter Limit Patch**

Okay, let's break this down. From what I'm seeing, `bm_register_write`, `bm_entry_write`, `bm_evict_inode`, and `load_misc_binary` are the key entry points here. The patch seems to be focused on a functional change within `binfmt_misc`, specifically limiting the number of pre-opened interpreters. This is an interesting approach to resource management, and I need to understand the implications better.

I see that `UCOUNT_BINFMT_MISC_INTERPRETERS` has been introduced, along with related definitions in `ucount.c` and `user_namespace.h`. That's where the core control likely resides. I'll need to look at how that counter is implemented and used.

Alright, the relevant config options are `CONFIG_BINFMT_MISC` and `CONFIG_USER_NS`. Makes sense; `CONFIG_USER_NS` is crucial for namespace-aware limits. Time to dive into `fs/Kconfig.binfmt` to confirm the details around `BINFMT_MISC`. I'm going to need to look at the interactions between these two config options. This should give me the configuration context for how to manage this interpreter limit.

{
  "Expression": "config BINFMT_MISC",
  "PathPrefix": "fs/Kconfig.binfmt"
}

{
  "Output": "fs/Kconfig.binfmt=138=config BINFMT_ZFLAT\n--\nfs/Kconfig.binfmt-144-\nfs/Kconfig.binfmt:145:config BINFMT_MISC\nfs/Kconfig.binfmt-146-\ttristate \"Kernel support for MISC binaries\"\n--\nfs/Kconfig.binfmt-170-\nfs/Kconfig.binfmt:171:config BINFMT_MISC_BPF\nfs/Kconfig.binfmt-172-\tbool \"BPF-selected interpreters for misc binaries\"\n"
}

gemini-3.1-pro-preview

null

null

							input: 13447
							output: 28
							thoughts: 18
						

Okay, here's my summary, taking the perspective of someone knowledgeable in the kernel:

**Delving into User Namespaces: Examining `kernel/ucount.c`**

Alright, let's get down to brass tacks. I need to refresh my memory, or perhaps confirm a hunch, about how user namespaces are handled in the kernel. My initial thought is to navigate directly to the heart of the matter – the `kernel/ucount.c` file. Specifically, I'm zeroing in on any code related to `USER_NS`. It's a key structure and mechanism, and that file is the most logical place to start digging into the intricacies of its implementation. I'm expecting to find the relevant functions, data structures, and any associated logic for managing user namespace resource accounting, perhaps user ID mapping, and how they interact with system calls. The code in `ucount.c` should illuminate how the kernel tracks and limits resource consumption within these isolated user environments. Knowing this detail will help me better understand the architecture of how user namespaces operate. I'll need to know this detail for later in this project.

{
  "Expression": "config USER_NS",
  "PathPrefix": "init/Kconfig"
}

{
  "Output": "init/Kconfig=1429=config IPC_NS\n--\ninit/Kconfig-1436-\ninit/Kconfig:1437:config USER_NS\ninit/Kconfig-1438-\tbool \"User namespace\"\n"
}

gemini-3.1-pro-preview

null

null

							input: 13801
							output: 65
							thoughts: 436
						

**Analyzing BINFMT_MISC and USER_NS for Relevant Symbols**

Okay, so I'm looking at `BINFMT_MISC` and `USER_NS` as my config context. The core functions I need to focus on are `bm_register_write`, `bm_entry_write`, `bm_evict_inode`, and `load_misc_binary`. Right now, it looks like `bm_entry_write` and `bm_register_write` are the crucial ones because *they* are what call `entry_attach_interpreter`, and that's the function that does the `inc_ucount`. On the flip side, `bm_evict_inode` is linked to `put_binfmt_handler`, which calls `entry_put_interpreters`, that then does the `dec_ucount` operation.

Let's drill down. `bm_register_write` looks solid; it handles writes to `/proc/sys/fs/binfmt_misc/register`.  `bm_entry_write` is similarly focused on writes to `/proc/sys/fs/binfmt_misc/<entry>`.  `bm_evict_inode` is triggered when a binfmt entry file gets removed. And `load_misc_binary` handles the case when a binary is executed. So, considering that, I'm definitely including `bm_register_write` and `bm_entry_write` in my analysis.

Now, a quick check on the static issue. `bm_register_write` *is* static, which seems a bit off given the instructions. But the instructions say to prefer non-static, non-inlined API entrypoints. However, these `bm_*` functions are assigned to `file_operations` structs. Their addresses are taken and they *aren't* inlined. Is there a non-static option?

`inc_ucount` and `dec_ucount` are exported, but those are just generic utilities. Let me check if `entry_attach_interpreter` is inlined. It's static, but that doesn't *automatically* mean it's inlined. Let me take a look at `fs/binfmt_misc.c` for some more options.

no matches

{
  "Expression": "^[a-zA-Z_][a-zA-Z0-9_]* [a-zA-Z_][a-zA-Z0-9_]*\\(",
  "PathPrefix": "fs/binfmt_misc.c"
}

{
  "error": "no matches"
}

gemini-3.1-pro-preview

null

null

							input: 14801
							output: 49
							thoughts: 21
						

Okay, let's dive into this. Here's how I'd approach this task, as if these were my internal thoughts:

**Finding Dynamic Functionality in `fs/binfmt_misc.c`**

Right, so the goal is to pinpoint non-static functions within `fs/binfmt_misc.c`. Why? Well, probably because I need to understand how the system dynamically handles executable formats, or perhaps I'm looking to extend its capabilities. Static functions are, by their nature, limited in scope, and often internal to a specific compilation unit. Non-static functions are the public interface, so to speak, of that file. They're the entry points, the hooks, the things that other parts of the kernel or even user-space might call into. Therefore, focusing on the non-static ones is the best first step. Let's see what's callable by other modules or the kernel as a whole. I expect these will be the functions managing the registration, loading, and perhaps even the execution of these miscellaneous binary formats. I need to understand how these formats are handled and what hooks are available. Time to start digging!

no matches

{
  "Expression": "^int [a-zA-Z_][a-zA-Z0-9_]*\\(",
  "PathPrefix": "fs/binfmt_misc.c"
}

{
  "error": "no matches"
}

gemini-3.1-pro-preview

null

null

							input: 15127
							output: 57
							thoughts: 16
						

Okay, here's my interpretation of those thoughts, crafted with the expectation that I'm discussing this with a fellow expert:

**Considering Potential Type Qualifiers for Size-Related Variables**

Alright, I'm diving into this design problem, and I'm at the point where I need to settle on a type qualifier for a variable likely to hold size information. I'm immediately thinking, "Let's see, what are the best options here?" My initial instinct leans towards trying `^void` or `^ssize_t`. I'm immediately trying to assess the tradeoffs. I'm running through my mental checklist: How does this impact portability? Is `^void` overly generic, or does it offer some potential for future flexibility? And what are the implications of using `^ssize_t`? I need to think this through: What's the target platform, and will it be the best option here?

no matches

{
  "Expression": "^(void|ssize_t|int) [a-zA-Z_][a-zA-Z0-9_]*\\(",
  "PathPrefix": "fs/binfmt_misc.c"
}

{
  "error": "no matches"
}

gemini-3.1-pro-preview

null

null

							input: 15409
							output: 35
							thoughts: 9
						

Okay, here's my interpretation of that thought process, tailored for an expert audience, and written in the first person:

**Initial Assessment: A Focused Approach**

Alright, the directive is clear. My first instinct, given the context, is to immediately engage with the core element: the file itself. There's no need to overthink the situation or get bogged down in ancillary concerns. Let's cut through the noise and directly assess the primary source of information. Jumping straight into the file is the most efficient and practical starting point. That initial scan and parse will inform my subsequent evaluation. This is where the real work begins.

{
  "File": "fs/binfmt_misc.c",
  "FirstLine": 1,
  "LineCount": 100
}

{
  "Contents": "   1:\t// SPDX-License-Identifier: GPL-2.0-only\n   2:\t/*\n   3:\t * binfmt_misc.c\n   4:\t *\n   5:\t * Copyright (C) 1997 Richard Günther\n   6:\t *\n   7:\t * binfmt_misc detects binaries via a magic or filename extension and invokes\n   8:\t * a specified wrapper. See Documentation/admin-guide/binfmt-misc.rst for more details.\n   9:\t */\n  10:\t\n  11:\t#define pr_fmt(fmt) KBUILD_MODNAME \": \" fmt\n  12:\t\n  13:\t#include \u003clinux/array_size.h\u003e\n  14:\t#include \u003clinux/binfmt_misc.h\u003e\n  15:\t#include \u003clinux/binfmts.h\u003e\n  16:\t#include \u003clinux/bitops.h\u003e\n  17:\t#include \u003clinux/bits.h\u003e\n  18:\t#include \u003clinux/bug.h\u003e\n  19:\t#include \u003clinux/cleanup.h\u003e\n  20:\t#include \u003clinux/cred.h\u003e\n  21:\t#include \u003clinux/ctype.h\u003e\n  22:\t#include \u003clinux/file.h\u003e\n  23:\t#include \u003clinux/fs.h\u003e\n  24:\t#include \u003clinux/fs_context.h\u003e\n  25:\t#include \u003clinux/init.h\u003e\n  26:\t#include \u003clinux/kstrtox.h\u003e\n  27:\t#include \u003clinux/limits.h\u003e\n  28:\t#include \u003clinux/list.h\u003e\n  29:\t#include \u003clinux/magic.h\u003e\n  30:\t#include \u003clinux/module.h\u003e\n  31:\t#include \u003clinux/printk.h\u003e\n  32:\t#include \u003clinux/rculist.h\u003e\n  33:\t#include \u003clinux/refcount.h\u003e\n  34:\t#include \u003clinux/seq_file.h\u003e\n  35:\t#include \u003clinux/slab.h\u003e\n  36:\t#include \u003clinux/srcu.h\u003e\n  37:\t#include \u003clinux/string.h\u003e\n  38:\t#include \u003clinux/string_helpers.h\u003e\n  39:\t#include \u003clinux/uaccess.h\u003e\n  40:\t#include \u003clinux/user_namespace.h\u003e\n  41:\t\n  42:\t#include \"internal.h\"\n  43:\t\n  44:\t/* Entry status and match type bit numbers. */\n  45:\tenum binfmt_misc_entry_bits {\n  46:\t\tMISC_FMT_ENABLED_BIT\t= 0,\n  47:\t\tMISC_FMT_MAGIC_BIT\t= 1,\n  48:\t\tMISC_FMT_BPF_BIT\t= 2,\n  49:\t};\n  50:\t\n  51:\t/* Entry behavior flags, fixed at registration time. */\n  52:\tenum binfmt_misc_entry_flags {\n  53:\t\tMISC_FMT_PRESERVE_ARGV0\t= (1U \u003c\u003c 31),\n  54:\t\tMISC_FMT_OPEN_BINARY\t= (1U \u003c\u003c 30),\n  55:\t\tMISC_FMT_CREDENTIALS\t= (1U \u003c\u003c 29),\n  56:\t\tMISC_FMT_OPEN_FILE\t= (1U \u003c\u003c 28),\n  57:\t\tMISC_FMT_TRANSPARENT\t= (1U \u003c\u003c 27),\n  58:\t\tMISC_FMT_LOADER\t\t= (1U \u003c\u003c 26),\n  59:\t\tMISC_FMT_DISABLED\t= (1U \u003c\u003c 25),\n  60:\t};\n  61:\t\n  62:\t/* The flags that shape the invocation; a 'B' handler picks those per exec. */\n  63:\t#define MISC_FMT_INVOCATION_FLAGS (MISC_FMT_PRESERVE_ARGV0 |\t\\\n  64:\t\t\t\t\t   MISC_FMT_OPEN_BINARY |\t\\\n  65:\t\t\t\t\t   MISC_FMT_CREDENTIALS |\t\\\n  66:\t\t\t\t\t   MISC_FMT_OPEN_FILE |\t\t\\\n  67:\t\t\t\t\t   MISC_FMT_TRANSPARENT |\t\\\n  68:\t\t\t\t\t   MISC_FMT_LOADER)\n  69:\t\n  70:\t/**\n  71:\t * struct binfmt_misc_flag - a flag character of the register string\n  72:\t * @c: the character userspace writes and reads back\n  73:\t * @flag: the entry flag it sets\n  74:\t * @implies: entry flags it turns on in addition\n  75:\t * @desc: what it does, for the registration debug output\n  76:\t */\n  77:\tstruct binfmt_misc_flag {\n  78:\t\tchar\t\tc;\n  79:\t\tunsigned long\tflag;\n  80:\t\tunsigned long\timplies;\n  81:\t\tconst char\t*desc;\n  82:\t};\n  83:\t\n  84:\tstatic const struct binfmt_misc_flag misc_flags[] = {\n  85:\t\t{ 'P', MISC_FMT_PRESERVE_ARGV0,\t0,\t\t\t\"preserve argv0\"\t\t},\n  86:\t\t{ 'O', MISC_FMT_OPEN_BINARY,\t0,\t\t\t\"open binary\"\t\t\t},\n  87:\t\t{ 'C', MISC_FMT_CREDENTIALS,\tMISC_FMT_OPEN_BINARY,\t\"credentials from the binary\"\t},\n  88:\t\t{ 'F', MISC_FMT_OPEN_FILE,\t0,\t\t\t\"open interpreter file now\"\t},\n  89:\t\t{ 'T', MISC_FMT_TRANSPARENT,\tMISC_FMT_OPEN_BINARY,\t\"transparent\"\t\t\t},\n  90:\t\t{ 'L', MISC_FMT_LOADER,\t\t0,\t\t\t\"loader substitution\"\t\t},\n  91:\t\t{ 'D', MISC_FMT_DISABLED,\t0,\t\t\t\"register disabled\"\t\t},\n  92:\t};\n  93:\t\n  94:\t/* Look up a flag character, NULL if @c is not one. */\n  95:\tstatic const struct binfmt_misc_flag *misc_flag_by_char(const char c)\n  96:\t{\n  97:\t\tfor (int i = 0; i \u003c ARRAY_SIZE(misc_flags); i++)\n  98:\t\t\tif (misc_flags[i].c == c)\n  99:\t\t\t\treturn \u0026misc_flags[i];\n 100:\t\treturn NULL;\n"
}

gemini-3.1-pro-preview

null

null

							input: 17282
							output: 31
							thoughts: 10
						

Okay, let's do this. Here's a summary of my internal thought process, tailored for an expert audience, and delivered in the first person:

**Navigating the Digital Landscape**

Alright, I'm at a point in this process where I've analyzed a specific part, and it's time to broaden my perspective. I've got a handle on the current element, but to be truly thorough, I need to zoom out. I'm thinking, "Let's check the rest of the file". This isn't just a casual glance; I'm mentally building context. I need to understand how this particular snippet fits into the broader architecture, the surrounding code, the overall data structure, the potential dependencies, and ultimately, the wider impact on the system. There could be critical connections and implicit assumptions, all of which might be revealed through broader context. So, I'll be going through the rest of the file to see how this area interacts with other parts.

{
  "Expression": "^static ",
  "PathPrefix": "fs/binfmt_misc.c"
}

{
  "Output": "fs/binfmt_misc.c=77=struct binfmt_misc_flag {\n--\nfs/binfmt_misc.c-83-\nfs/binfmt_misc.c:84:static const struct binfmt_misc_flag misc_flags[] = {\nfs/binfmt_misc.c-85-\t{ 'P', MISC_FMT_PRESERVE_ARGV0,\t0,\t\t\t\"preserve argv0\"\t\t},\n--\nfs/binfmt_misc.c-94-/* Look up a flag character, NULL if @c is not one. */\nfs/binfmt_misc.c:95:static const struct binfmt_misc_flag *misc_flag_by_char(const char c)\nfs/binfmt_misc.c-96-{\n--\nfs/binfmt_misc.c=140=DEFINE_STATIC_SRCU_FAST(bm_entries_srcu);\n--\nfs/binfmt_misc.c-142-/* Check if @e's magic matches @bprm's buffer, applying the mask if set. */\nfs/binfmt_misc.c:143:static bool entry_matches_magic(const struct binfmt_misc_entry *e,\nfs/binfmt_misc.c-144-\t\t\t\tconst struct linux_binprm *bprm)\n--\nfs/binfmt_misc.c-158-/* Check if @e's registered extension matches @ext, NULL if there is none. */\nfs/binfmt_misc.c:159:static bool entry_matches_extension(const struct binfmt_misc_entry *e,\nfs/binfmt_misc.c-160-\t\t\t\t    const char *ext)\n--\nfs/binfmt_misc.c-181- */\nfs/binfmt_misc.c:182:static struct binfmt_misc_entry *\nfs/binfmt_misc.c-183-search_binfmt_handler(struct binfmt_misc *misc, struct linux_binprm *bprm)\n--\nfs/binfmt_misc.c-230- */\nfs/binfmt_misc.c:231:static struct binfmt_misc_entry *get_binfmt_handler(struct binfmt_misc *misc,\nfs/binfmt_misc.c-232-\t\t\t\t\t\t    struct linux_binprm *bprm)\n--\nfs/binfmt_misc.c=246=binfmt_misc_find_interp(const struct list_head *interps, const char *name)\n--\nfs/binfmt_misc.c-256-/* Undo the open_exec() a pre-opened interpreter file came from. */\nfs/binfmt_misc.c:257:static void close_interp_file(struct file *f)\nfs/binfmt_misc.c-258-{\n--\nfs/binfmt_misc.c=265=DEFINE_FREE(close_interp_file, struct file *, close_interp_file(_T))\n--\nfs/binfmt_misc.c-272- */\nfs/binfmt_misc.c:273:static struct file *open_interp_file(const struct cred *cred, const char *path)\nfs/binfmt_misc.c-274-{\n--\nfs/binfmt_misc.c-284-/* Release the interpreters an entry was registered with. */\nfs/binfmt_misc.c:285:static void entry_put_interpreters(struct binfmt_misc_entry *e)\nfs/binfmt_misc.c-286-{\n--\nfs/binfmt_misc.c-313- */\nfs/binfmt_misc.c:314:static int entry_attach_interpreter(struct binfmt_misc_entry *e,\nfs/binfmt_misc.c-315-\t\t\t\t    const char *name, const char *path,\n--\nfs/binfmt_misc.c-351-\nfs/binfmt_misc.c:352:static void bm_entry_free_rcu(struct rcu_head *rcu)\nfs/binfmt_misc.c-353-{\n--\nfs/binfmt_misc.c-370- */\nfs/binfmt_misc.c:371:static void put_binfmt_handler(struct binfmt_misc_entry *e)\nfs/binfmt_misc.c-372-{\n--\nfs/binfmt_misc.c=383=DEFINE_FREE(put_binfmt_handler, struct binfmt_misc_entry *, put_binfmt_handler(_T))\n--\nfs/binfmt_misc.c-385-/* Drop everything a load program staged for this exec. */\nfs/binfmt_misc.c:386:static void drop_staged_selection(struct linux_binprm *bprm)\nfs/binfmt_misc.c-387-{\n--\nfs/binfmt_misc.c-410- */\nfs/binfmt_misc.c:411:static struct binfmt_misc *current_binfmt_misc(void)\nfs/binfmt_misc.c-412-{\n--\nfs/binfmt_misc.c-437- */\nfs/binfmt_misc.c:438:static const char *entry_select_interpreter(const struct binfmt_misc_entry *e,\nfs/binfmt_misc.c-439-\t\t\t\t\t    struct linux_binprm *bprm)\n--\nfs/binfmt_misc.c-488- */\nfs/binfmt_misc.c:489:static unsigned long entry_invocation_flags(const struct binfmt_misc_entry *e,\nfs/binfmt_misc.c-490-\t\t\t\t\t    struct linux_binprm *bprm)\n--\nfs/binfmt_misc.c-527- */\nfs/binfmt_misc.c:528:static struct file *entry_open_interpreter(const struct binfmt_misc_entry *e,\nfs/binfmt_misc.c-529-\t\t\t\t\t   struct linux_binprm *bprm,\n--\nfs/binfmt_misc.c-570- */\nfs/binfmt_misc.c:571:static int build_interp_argv(struct linux_binprm *bprm, const char *interpreter,\nfs/binfmt_misc.c-572-\t\t\t     unsigned long flags)\n--\nfs/binfmt_misc.c-620- */\nfs/binfmt_misc.c:621:static int load_misc_binary(struct linux_binprm *bprm)\nfs/binfmt_misc.c-622-{\n--\nfs/binfmt_misc.c-702- */\nfs/binfmt_misc.c:703:static char *scanarg(char *s, char del)\nfs/binfmt_misc.c-704-{\n--\nfs/binfmt_misc.c-720-/* Parse the 'flags' field, stopping at the first character that is not one. */\nfs/binfmt_misc.c:721:static char *check_special_flags(char *p, struct binfmt_misc_entry *e)\nfs/binfmt_misc.c-722-{\n--\nfs/binfmt_misc.c-733-/* Parse the 'offset', 'magic' and 'mask' fields of an 'M' entry. */\nfs/binfmt_misc.c:734:static char *parse_magic_fields(struct binfmt_misc_entry *e, char *p, char del)\nfs/binfmt_misc.c-735-{\n--\nfs/binfmt_misc.c-794-/* Parse the 'magic' field of an 'E' entry: the filename extension. */\nfs/binfmt_misc.c:795:static char *parse_extension_fields(struct binfmt_misc_entry *e, char *p,\nfs/binfmt_misc.c-796-\t\t\t\t    char del)\n--\nfs/binfmt_misc.c-825- */\nfs/binfmt_misc.c:826:static char *parse_bpf_fields(struct binfmt_misc_entry *e, char *p, char del)\nfs/binfmt_misc.c-827-{\n--\nfs/binfmt_misc.c-847- */\nfs/binfmt_misc.c:848:static struct binfmt_misc_entry *create_entry(const char __user *buffer,\nfs/binfmt_misc.c-849-\t\t\t\t\t      size_t count)\n--\nfs/binfmt_misc.c=1001=enum bm_command {\n--\nfs/binfmt_misc.c-1014- */\nfs/binfmt_misc.c:1015:static int parse_command(const char *s, size_t count)\nfs/binfmt_misc.c-1016-{\n--\nfs/binfmt_misc.c-1032-/* Copy in a command from a file that takes nothing else, and parse it. */\nfs/binfmt_misc.c:1033:static int read_command(const char __user *buffer, size_t count)\nfs/binfmt_misc.c-1034-{\n--\nfs/binfmt_misc.c-1046-/* The root directory's inode; its lock serializes configuring an instance. */\nfs/binfmt_misc.c:1047:static struct inode *bm_root_inode(struct super_block *sb)\nfs/binfmt_misc.c-1048-{\n--\nfs/binfmt_misc.c-1051-\nfs/binfmt_misc.c:1052:static void bm_seq_hex(struct seq_file *m, const u8 *data, int size)\nfs/binfmt_misc.c-1053-{\n--\nfs/binfmt_misc.c-1057-\nfs/binfmt_misc.c:1058:static int bm_entry_show(struct seq_file *m, void *unused)\nfs/binfmt_misc.c-1059-{\n--\nfs/binfmt_misc.c-1107-\nfs/binfmt_misc.c:1108:static struct inode *bm_get_inode(struct super_block *sb, umode_t mode)\nfs/binfmt_misc.c-1109-{\n--\nfs/binfmt_misc.c-1130- */\nfs/binfmt_misc.c:1131:static struct binfmt_misc *i_binfmt_misc(struct inode *inode)\nfs/binfmt_misc.c-1132-{\n--\nfs/binfmt_misc.c-1148-*/\nfs/binfmt_misc.c:1149:static void bm_evict_inode(struct inode *inode)\nfs/binfmt_misc.c-1150-{\n--\nfs/binfmt_misc.c-1178- */\nfs/binfmt_misc.c:1179:static void unlink_binfmt_handler(struct binfmt_misc *misc,\nfs/binfmt_misc.c-1180-\t\t\t\t  struct binfmt_misc_entry *e)\n--\nfs/binfmt_misc.c-1194- */\nfs/binfmt_misc.c:1195:static void remove_binfmt_handler(struct binfmt_misc *misc,\nfs/binfmt_misc.c-1196-\t\t\t\t  struct binfmt_misc_entry *e)\n--\nfs/binfmt_misc.c-1202-/* Remove @e unless it was already removed. */\nfs/binfmt_misc.c:1203:static void bm_remove_entry(struct binfmt_misc_entry *e, struct super_block *sb)\nfs/binfmt_misc.c-1204-{\n--\nfs/binfmt_misc.c-1214-/* Remove all entries of the binfmt_misc instance @misc belonging to @sb. */\nfs/binfmt_misc.c:1215:static void bm_remove_all_entries(struct binfmt_misc *misc,\nfs/binfmt_misc.c-1216-\t\t\t\t  struct super_block *sb)\n--\nfs/binfmt_misc.c-1245- */\nfs/binfmt_misc.c:1246:static int bm_unlink(struct inode *dir, struct dentry *dentry)\nfs/binfmt_misc.c-1247-{\n--\nfs/binfmt_misc.c-1256-\nfs/binfmt_misc.c:1257:static const struct inode_operations bm_dir_inode_operations = {\nfs/binfmt_misc.c-1258-\t.lookup\t\t= simple_lookup,\n--\nfs/binfmt_misc.c-1263-\nfs/binfmt_misc.c:1264:static int bm_entry_open(struct inode *inode, struct file *file)\nfs/binfmt_misc.c-1265-{\n--\nfs/binfmt_misc.c-1300- */\nfs/binfmt_misc.c:1301:static ssize_t bm_entry_add_interp(struct binfmt_misc_entry *e,\nfs/binfmt_misc.c-1302-\t\t\t\t   struct file *file, char *buf, size_t count)\n--\nfs/binfmt_misc.c-1361-\nfs/binfmt_misc.c:1362:static ssize_t bm_entry_write(struct file *file, const char __user *buffer,\nfs/binfmt_misc.c-1363-\t\t\t\tsize_t count, loff_t *ppos)\n--\nfs/binfmt_misc.c-1419-\nfs/binfmt_misc.c:1420:static const struct file_operations bm_entry_operations = {\nfs/binfmt_misc.c-1421-\t.open\t\t= bm_entry_open,\n--\nfs/binfmt_misc.c-1430-/* add to filesystem */\nfs/binfmt_misc.c:1431:static int add_entry(struct binfmt_misc_entry *e, struct super_block *sb)\nfs/binfmt_misc.c-1432-{\n--\nfs/binfmt_misc.c-1461-\nfs/binfmt_misc.c:1462:static ssize_t bm_register_write(struct file *file, const char __user *buffer,\nfs/binfmt_misc.c-1463-\t\t\t       size_t count, loff_t *ppos)\n--\nfs/binfmt_misc.c-1502-\nfs/binfmt_misc.c:1503:static const struct file_operations bm_register_operations = {\nfs/binfmt_misc.c-1504-\t.write\t\t= bm_register_write,\n--\nfs/binfmt_misc.c-1509-\nfs/binfmt_misc.c:1510:static ssize_t\nfs/binfmt_misc.c-1511-bm_status_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)\n--\nfs/binfmt_misc.c-1520-\nfs/binfmt_misc.c:1521:static ssize_t bm_status_write(struct file *file, const char __user *buffer,\nfs/binfmt_misc.c-1522-\t\tsize_t count, loff_t *ppos)\n--\nfs/binfmt_misc.c-1544-\nfs/binfmt_misc.c:1545:static const struct file_operations bm_status_operations = {\nfs/binfmt_misc.c-1546-\t.read\t\t= bm_status_read,\n--\nfs/binfmt_misc.c-1552-\nfs/binfmt_misc.c:1553:static const struct super_operations bm_super_ops = {\nfs/binfmt_misc.c-1554-\t.statfs\t\t= simple_statfs,\n--\nfs/binfmt_misc.c-1557-\nfs/binfmt_misc.c:1558:static int bm_fill_super(struct super_block *sb, struct fs_context *fc)\nfs/binfmt_misc.c-1559-{\n--\nfs/binfmt_misc.c-1630-\nfs/binfmt_misc.c:1631:static void bm_free(struct fs_context *fc)\nfs/binfmt_misc.c-1632-{\n--\nfs/binfmt_misc.c-1636-\nfs/binfmt_misc.c:1637:static int bm_get_tree(struct fs_context *fc)\nfs/binfmt_misc.c-1638-{\n--\nfs/binfmt_misc.c-1641-\nfs/binfmt_misc.c:1642:static const struct fs_context_operations bm_context_ops = {\nfs/binfmt_misc.c-1643-\t.free\t\t= bm_free,\n--\nfs/binfmt_misc.c-1646-\nfs/binfmt_misc.c:1647:static void bm_kill_sb(struct super_block *sb)\nfs/binfmt_misc.c-1648-{\n--\nfs/binfmt_misc.c-1654-\nfs/binfmt_misc.c:1655:static int bm_init_fs_context(struct fs_context *fc)\nfs/binfmt_misc.c-1656-{\n--\nfs/binfmt_misc.c-1660-\nfs/binfmt_misc.c:1661:static struct linux_binfmt misc_format = {\nfs/binfmt_misc.c-1662-\t.module = THIS_MODULE,\n--\nfs/binfmt_misc.c-1665-\nfs/binfmt_misc.c:1666:static struct file_system_type bm_fs_type = {\nfs/binfmt_misc.c-1667-\t.owner\t\t= THIS_MODULE,\n--\nfs/binfmt_misc.c=1673=MODULE_ALIAS_FS(\"binfmt_misc\");\nfs/binfmt_misc.c-1674-\nfs/binfmt_misc.c:1675:static int __init init_misc_binfmt(void)\nfs/binfmt_misc.c-1676-{\n--\nfs/binfmt_misc.c-1682-\nfs/binfmt_misc.c:1683:static void __exit exit_misc_binfmt(void)\nfs/binfmt_misc.c-1684-{\n"
}

gemini-3.1-pro-preview

null

null

							input: 22224
							output: 172
							thoughts: 894
						

**Analyzing the BinFmt Misc Patch for Fuzzing Potential**

Okay, let's break this down systematically. My initial thought was to identify the key functions or "focus symbols" that are affected by this patch and would make good targets for fuzzing. I started by looking for non-static, non-inlined API entrypoints – those are the most stable and easily accessible points of interaction. Initially, `binfmt_misc_find_interp` caught my eye, but it's not a true API entry point. Then I noticed that `load_misc_binary` *is* static, but is assigned to `misc_format.load_binary`. Similarly, I saw `bm_register_write` assigned to `bm_register_operations.write`, `bm_entry_write` assigned to `bm_entry_operations.write`, and `bm_evict_inode` assigned to `bm_super_ops.evict_inode`. These assignments, specifically to the function pointers, made me realize these are indeed the right places to focus.

Looking at the code more closely, it seems that `load_misc_binary` doesn't directly interact with `UCOUNT_BINFMT_MISC_INTERPRETERS`, meaning it's less relevant. The patch seems to be specifically modifying `entry_attach_interpreter` and `entry_put_interpreters`, the critical functions. `entry_attach_interpreter` is called by `bm_entry_add_interp` and `bm_register_write`, where `bm_entry_add_interp` is called by `bm_entry_write`.  `entry_put_interpreters` is called by `put_binfmt_handler`, which is called by several functions, including `bm_entry_free_rcu`, `load_misc_binary`, `create_entry`, `bm_evict_inode`, and `bm_register_write`.

After this, I re-evaluated and decided that `bm_register_write`, `bm_entry_write`, and `bm_evict_inode` are the best focus symbols, however, since `bm_register_write` and `bm_entry_write` are assigned to function pointers in the `file_operations` structure, they won't be inlined.

Now, let's move onto the configurations.  I checked for relevant configurations and identified `CONFIG_BINFMT_MISC` and `CONFIG_USER_NS`. However, checking the dependencies of `CONFIG_USER_NS` and discovering it depends on `MULTIUSER` and `NAMESPACES` and since `USER_NS` is usually enabled in syzkaller, I will just list `BINFMT_MISC` and `USER_NS`.

Double-checking `fs/Kconfig.binfmt` for `BINFMT_MISC` confirmed it has no special dependencies.  Reviewing `kernel/ucount.c` for `UCOUNT_BINFMT_MISC_INTERPRETERS` solidifies that `BINFMT_MISC` is the only truly necessary configuration.

Finally, a quick review of the patch's core functionality: it's adding a limit to the number of pre-opened interpreters in `binfmt_misc`, using `inc_ucount` and `dec_ucount` for the count. The limit itself is set via `/proc/sys/user/max_binfmt_misc_interpreters`. The patch touches `entry_attach_interpreter` to charge and `entry_put_interpreters` to uncharge, which is reachable from userspace. It's definitely a functional change and worth fuzzing.

Therefore, the focus symbols are:
- `bm_register_write`
- `bm_entry_write`
- `bm_evict_inode`

And the required configurations:
- `BINFMT_MISC`
- `USER_NS`

Time to `set-results`.

{
  "EnableConfigs": [
    "BINFMT_MISC",
    "USER_NS"
  ],
  "FocusSymbols": [
    "bm_register_write",
    "bm_entry_write",
    "bm_evict_inode"
  ],
  "Reasoning": "The patch introduces a new sysctl limit `max_binfmt_misc_interpreters` to restrict the number of pre-opened interpreters in `binfmt_misc` using `ucounts`. This is a functional change to the core kernel and `binfmt_misc` filesystem that is reachable from userspace by unprivileged users (in a user namespace). Fuzzing should focus on the registration and removal of `binfmt_misc` entries to test the charging and uncharging of the budget.",
  "WorthFuzzing": true
}

{
  "EnableConfigs": [
    "BINFMT_MISC",
    "USER_NS"
  ],
  "FocusSymbols": [
    "bm_register_write",
    "bm_entry_write",
    "bm_evict_inode"
  ],
  "Reasoning": "The patch introduces a new sysctl limit `max_binfmt_misc_interpreters` to restrict the number of pre-opened interpreters in `binfmt_misc` using `ucounts`. This is a functional change to the core kernel and `binfmt_misc` filesystem that is reachable from userspace by unprivileged users (in a user namespace). Fuzzing should focus on the registration and removal of `binfmt_misc` entries to test the charging and uncharging of the budget.",
  "WorthFuzzing": true
}