AI Trajectory

null

{
  "EnableConfigs": [
    "BPF_SYSCALL"
  ],
  "FocusSymbols": [
    "reparent_dynptr_slices_on_func_exit",
    "prepare_func_exit"
  ],
  "KMSANReasoning": "The patch modifies the BPF verifier's `prepare_func_exit()` logic by adding `reparent_dynptr_slices_on_func_exit()`. This ensures that dynptr slices escaping a subprogram call frame have their `parent_id` updated to point to the dynptr's parent, properly invalidating slices when the parent dynptr/buffer is destroyed in the caller.\n\nThis fix prevents Use-After-Free (UAF) / dangling pointer dereferences in BPF programs. Such runtime memory safety violations are caught by KASAN. The patch does not introduce or expose uninitialized memory reads, uninitialized struct fields, or kernel-to-user info-leaks. Therefore, KMSAN is not needed.",
  "NeedsKMSAN": false,
  "Reasoning": "The patch introduces reparent_dynptr_slices_on_func_exit() in kernel/bpf/verifier.c, called from prepare_func_exit() to update dynptr lineage tracking when callee frames return. This modifies core BPF verifier logic reachable via BPF program loading syscalls.",
  "WorthFuzzing": true
}

null

{
  "PatchDiff": "commit 0b4dc9b2876ab4cea9413c2d84ace96714063bd3\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate:   Thu Sep 10 04:49:18 2026 +0000\n\n    syz-cluster: applied patch under review\n\ndiff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c\nindex 72a3f5998dd27..ee41b7386f752 100644\n--- a/kernel/bpf/verifier.c\n+++ b/kernel/bpf/verifier.c\n@@ -800,6 +800,39 @@ static int dynptr_ref_cnt(struct bpf_verifier_env *env, int v_parent_id)\n \treturn ref_cnt;\n }\n \n+static void reparent_dynptr_slices_on_func_exit(struct bpf_verifier_env *env,\n+\t\t\t\t\t\tstruct bpf_func_state *callee)\n+{\n+\tstruct bpf_verifier_state *vstate = env-\u003ecur_state;\n+\tstruct bpf_func_state *state;\n+\tstruct bpf_reg_state *reg;\n+\tint i;\n+\n+\tfor (i = 0; i \u003c callee-\u003eallocated_stack / BPF_REG_SIZE; i++) {\n+\t\tstruct bpf_stack_state *slot = \u0026callee-\u003estack[i];\n+\t\tstruct bpf_reg_state *dynptr = \u0026slot-\u003espilled_ptr;\n+\n+\t\tif (slot-\u003eslot_type[0] != STACK_DYNPTR ||\n+\t\t    !dynptr-\u003edynptr.first_slot ||\n+\t\t    !dynptr-\u003eparent_id)\n+\t\t\tcontinue;\n+\n+\t\t/*\n+\t\t * A callee can spill a slice derived from its local dynptr into\n+\t\t * the caller's stack. The slice then outlives the dynptr id that\n+\t\t * links it to the rest of the object tree. Preserve that link by\n+\t\t * making escaped slices children of the dynptr's parent before\n+\t\t * the callee frame is freed.\n+\t\t */\n+\t\tbpf_for_each_reg_in_vstate(vstate, state, reg, ({\n+\t\t\tif (state == callee || reg-\u003eparent_id != dynptr-\u003eid ||\n+\t\t\t    base_type(reg-\u003etype) != PTR_TO_MEM)\n+\t\t\t\tcontinue;\n+\t\t\treg-\u003eparent_id = dynptr-\u003eparent_id;\n+\t\t}));\n+\t}\n+}\n+\n static int destroy_if_dynptr_stack_slot(struct bpf_verifier_env *env,\n \t\t\t\t        struct bpf_func_state *state, int spi)\n {\n@@ -10399,6 +10432,7 @@ static int prepare_func_exit(struct bpf_verifier_env *env, int *insn_idx)\n \t\tprint_verifier_state(env, state, caller-\u003eframeno, true);\n \t}\n \taccount_processed_insns(env, callee, caller);\n+\treparent_dynptr_slices_on_func_exit(env, callee);\n \t/* clear everything in the callee. In case of exceptional exits using\n \t * bpf_throw, this will be done by copy_verifier_state for extra frames. */\n \tfree_func_state(callee);\ndiff --git a/tools/testing/selftests/bpf/prog_tests/bpf_qdisc.c b/tools/testing/selftests/bpf/prog_tests/bpf_qdisc.c\nindex 6dbd1487343c0..122ecb7e98e2a 100644\n--- a/tools/testing/selftests/bpf/prog_tests/bpf_qdisc.c\n+++ b/tools/testing/selftests/bpf/prog_tests/bpf_qdisc.c\n@@ -11,6 +11,7 @@\n #include \"bpf_qdisc_fail__invalid_dynptr.skel.h\"\n #include \"bpf_qdisc_fail__invalid_dynptr_slice.skel.h\"\n #include \"bpf_qdisc_fail__invalid_dynptr_cross_frame.skel.h\"\n+#include \"bpf_qdisc_fail__invalid_dynptr_returned_slice.skel.h\"\n #include \"bpf_qdisc_fail__untrusted_write.skel.h\"\n #include \"bpf_qdisc_dynptr_use_after_invalidate_clone.skel.h\"\n \n@@ -230,6 +231,7 @@ void test_ns_bpf_qdisc(void)\n \t\ttest_incompl_ops();\n \tRUN_TESTS(bpf_qdisc_fail__invalid_dynptr);\n \tRUN_TESTS(bpf_qdisc_fail__invalid_dynptr_cross_frame);\n+\tRUN_TESTS(bpf_qdisc_fail__invalid_dynptr_returned_slice);\n \tRUN_TESTS(bpf_qdisc_fail__invalid_dynptr_slice);\n \tRUN_TESTS(bpf_qdisc_fail__untrusted_write);\n \tRUN_TESTS(bpf_qdisc_dynptr_use_after_invalidate_clone);\ndiff --git a/tools/testing/selftests/bpf/progs/bpf_qdisc_fail__invalid_dynptr_returned_slice.c b/tools/testing/selftests/bpf/progs/bpf_qdisc_fail__invalid_dynptr_returned_slice.c\nnew file mode 100644\nindex 0000000000000..940aba7d8abfe\n--- /dev/null\n+++ b/tools/testing/selftests/bpf/progs/bpf_qdisc_fail__invalid_dynptr_returned_slice.c\n@@ -0,0 +1,76 @@\n+// SPDX-License-Identifier: GPL-2.0\n+\n+#include \u003cvmlinux.h\u003e\n+#include \"bpf_experimental.h\"\n+#include \"bpf_qdisc_common.h\"\n+#include \"bpf_misc.h\"\n+\n+char _license[] SEC(\"license\") = \"GPL\";\n+\n+int proto;\n+\n+static __noinline struct ethhdr *slice_in_subprog(struct sk_buff *skb)\n+{\n+\tstruct bpf_dynptr ptr;\n+\n+\tbpf_dynptr_from_skb((struct __sk_buff *)skb, 0, \u0026ptr);\n+\treturn bpf_dynptr_slice(\u0026ptr, 0, NULL, sizeof(struct ethhdr));\n+}\n+\n+SEC(\"struct_ops\")\n+__failure __msg(\"invalid mem access 'scalar'\")\n+int BPF_PROG(invalid_dynptr_returned_slice, struct sk_buff *skb,\n+\t     struct Qdisc *sch, struct bpf_sk_buff_ptr *to_free)\n+{\n+\tstruct ethhdr *hdr;\n+\n+\thdr = slice_in_subprog(skb);\n+\tif (!hdr) {\n+\t\tbpf_qdisc_skb_drop(skb, to_free);\n+\t\treturn NET_XMIT_DROP;\n+\t}\n+\n+\tbpf_qdisc_skb_drop(skb, to_free);\n+\n+\t/* this should fail */\n+\tproto = hdr-\u003eh_proto;\n+\n+\treturn NET_XMIT_DROP;\n+}\n+\n+SEC(\"struct_ops\")\n+__auxiliary\n+struct sk_buff *BPF_PROG(bpf_qdisc_test_dequeue, struct Qdisc *sch)\n+{\n+\treturn NULL;\n+}\n+\n+SEC(\"struct_ops\")\n+__auxiliary\n+int BPF_PROG(bpf_qdisc_test_init, struct Qdisc *sch, struct nlattr *opt,\n+\t     struct netlink_ext_ack *extack)\n+{\n+\treturn 0;\n+}\n+\n+SEC(\"struct_ops\")\n+__auxiliary\n+void BPF_PROG(bpf_qdisc_test_reset, struct Qdisc *sch)\n+{\n+}\n+\n+SEC(\"struct_ops\")\n+__auxiliary\n+void BPF_PROG(bpf_qdisc_test_destroy, struct Qdisc *sch)\n+{\n+}\n+\n+SEC(\".struct_ops\")\n+struct Qdisc_ops test = {\n+\t.enqueue   = (void *)invalid_dynptr_returned_slice,\n+\t.dequeue   = (void *)bpf_qdisc_test_dequeue,\n+\t.init      = (void *)bpf_qdisc_test_init,\n+\t.reset     = (void *)bpf_qdisc_test_reset,\n+\t.destroy   = (void *)bpf_qdisc_test_destroy,\n+\t.id        = \"bpf_qdisc_test\",\n+};\ndiff --git a/tools/testing/selftests/bpf/progs/dynptr_fail.c b/tools/testing/selftests/bpf/progs/dynptr_fail.c\nindex 1cd61d72c166f..92f9f9ea05321 100644\n--- a/tools/testing/selftests/bpf/progs/dynptr_fail.c\n+++ b/tools/testing/selftests/bpf/progs/dynptr_fail.c\n@@ -1892,6 +1892,55 @@ int clone_invalidate4(void *ctx)\n \treturn 0;\n }\n \n+static __noinline void clone_slice_in_subprog(struct bpf_dynptr *ptr, int **data)\n+{\n+\tstruct bpf_dynptr clone;\n+\n+\tbpf_dynptr_clone(ptr, \u0026clone);\n+\t*data = bpf_dynptr_data(\u0026clone, 0, sizeof(val));\n+}\n+\n+/*\n+ * A slice that escapes the clone's call frame remains valid while the\n+ * shared ringbuf reservation is live.\n+ */\n+SEC(\"?raw_tp\")\n+__success\n+int clone_slice_returned_frame_valid(void *ctx)\n+{\n+\tstruct bpf_dynptr ptr;\n+\tint *data = NULL;\n+\n+\tbpf_ringbuf_reserve_dynptr(\u0026ringbuf, val, 0, \u0026ptr);\n+\tclone_slice_in_subprog(\u0026ptr, \u0026data);\n+\tif (data)\n+\t\t*data = 123;\n+\tbpf_ringbuf_submit_dynptr(\u0026ptr, 0);\n+\n+\treturn 0;\n+}\n+\n+/*\n+ * Releasing the shared reservation must invalidate a slice that escaped\n+ * from a clone's call frame.\n+ */\n+SEC(\"?raw_tp\")\n+__failure __msg(\"invalid mem access 'scalar'\")\n+int clone_slice_returned_frame_invalid(void *ctx)\n+{\n+\tstruct bpf_dynptr ptr;\n+\tint *data = NULL;\n+\n+\tbpf_ringbuf_reserve_dynptr(\u0026ringbuf, val, 0, \u0026ptr);\n+\tclone_slice_in_subprog(\u0026ptr, \u0026data);\n+\tbpf_ringbuf_submit_dynptr(\u0026ptr, 0);\n+\tif (data)\n+\t\t/* this should fail */\n+\t\t*data = 123;\n+\n+\treturn 0;\n+}\n+\n /* Invalidating a dynptr should invalidate any data slices\n  * of its parent\n  */\n"
}

core

null

{
  "EnableConfigs": [
    "BPF_SYSCALL"
  ],
  "FocusSymbols": [
    "reparent_dynptr_slices_on_func_exit",
    "prepare_func_exit"
  ],
  "Reasoning": "The patch introduces reparent_dynptr_slices_on_func_exit() in kernel/bpf/verifier.c, called from prepare_func_exit() to update dynptr lineage tracking when callee frames return. This modifies core BPF verifier logic reachable via BPF program loading syscalls.",
  "WorthFuzzing": true
}

You are an expert Linux kernel maintainer and security engineer.
Your job is to review a provided patch series and evaluate whether it warrants fuzzing with syzkaller.

IMPORTANT: The changes have ALREADY been applied and committed as the HEAD commit in
your workspace. Do NOT rely on internal assumptions. You must actively use your code access
tools to inspect the actual source code, callers, and surrounding context.

================================================================================
1. CORE TRIAGE PHILOSOPHY
================================================================================
The goal of patch fuzzing is to discover crashes, regressions, exposed latent bugs,
and newly triggered assertions introduced by the patch series.

- REACHABILITY IS THE PRIMARY GATE:
  Fuzzing can only discover bugs in code that can actually execute in standard virtualized
  environments (GCE or QEMU, utilizing software-emulated devices like USB gadgets, netdev, tun/tap).
  If the modified code is structurally unreachable (see Section 2), it MUST NOT be fuzzed,
  regardless of whether it adds assertions or complex logic.

- DO NOT BLINDLY TRUST "NO FUNCTIONAL CHANGE" (NFCI) OR "REFACTORING" CLAIMS:
  Patch authors routinely label changes as "cleanups", "refactorings", or state
  "No functional change intended". Do NOT take these claims at face value.
  Code refactorings that rearrange logic, introduce helper functions, or alter state management
  in core subsystems frequently introduce subtle semantic shifts or uncover latent kernel bugs.
  If reachable executable code is modified or refactored, it MUST be fuzzed.

- NEW OR MODIFIED ASSERTIONS IN REACHABLE CODE MUST BE FUZZED:
  When a patch introduces or modifies runtime checks or assertions (e.g., WARN_ON*, VM_WARN_ON*,
  BUG_ON*, lockdep_assert*) in reachable code paths, it enforces new or stricter invariants.
  Even if the author believes the invariant always holds, fuzzing is essential to verify whether
  an unusual sequence of operations can violate it.

================================================================================
2. WHEN TO RETURN WorthFuzzing=false (NEGATIVE CRITERIA)
================================================================================
Return WorthFuzzing=false ONLY IF all modified code falls strictly into one or more of these categories:

- Non-kernel and non-executable changes:
  * Modifications to Documentation/, comments, or spelling fixes.
  * User-space directories, self-tests, samples, or scripts (e.g., tools/, samples/, scripts/, usr/)
    that do not affect the compiled kernel image (vmlinux) or kernel modules.
  * Purely decorative logging (e.g., message strings in pr_err, printk, dev_info) or tracepoints
    that do not alter control flow or data structures.
  * Build system or Kconfig changes that do not alter compiled C logic.
- Structurally unreachable hardware:
  * Vendor-specific PCIe switches, SmartNICs, or GPU drivers (e.g., mlxsw, pds_core, qed,
    ionic, amdgpu) requiring physical ASIC/PCIe cards not emulated in standard QEMU.
- Unreachable execution paths:
  * Driver teardown callbacks (.remove, .shutdown, pci_unregister_driver) executed only during
    physical PCI hot-unplug or manual sysfs driver unbinding.
  * Code paths exclusive to architectures other than the target architecture.

================================================================================
3. WHEN TO RETURN WorthFuzzing=true (POSITIVE CRITERIA)
================================================================================
Return WorthFuzzing=true whenever the patch touches reachable executable code, including:
- Core Subsystems:
  * Any logic modifications in memory management (mm/), synchronization/locking (kernel/locking/),
    BPF, scheduler, core networking, VFS, or syscall handling.
- Refactorings and Code Cleanups:
  * Any restructuring of reachable data structures, helper abstractions, or algorithm flows.
- Runtime Assertions and Defensive Checks:
  * Any introduction or alteration of assertions (WARN_ON*, VM_WARN_ON*, BUG_ON*, etc.) in reachable paths.
- Reachable Drivers and Protocols:
  * Drivers accessible via virtual buses (virtio, USB gadget, loopback, netlink, binder, sockets, etc.).

================================================================================
4. EXTRACTING FocusSymbols (PREVENTING DILUTION)
================================================================================
When WorthFuzzing=true, you must extract specific kernel functions into FocusSymbols to guide the fuzzer:

- AVOID UBIQUITOUS LIFECYCLE HOT-PATHS:
  Do NOT list generic, ubiquitous functions called by almost every program in the corpus
  (including, but not limited to: general memory allocators and deallocators, page fault
  and trap handlers, or core synchronization primitives; this is not an exhaustive list).
  Listing ubiquitous functions causes the fuzzer to classify thousands of unrelated tests as "focused",
  which severely dilutes fuzzing effort away from the actual changes.

- TARGET SPECIFIC FEATURE LOGIC AND ENTRYPOINTS:
  List functions that specifically implement the logic being added or altered, or direct API entrypoints
  for the subsystem feature under review.

- HANDLING STATIC INLINE FUNCTIONS IN HEADERS (.h):
  Compiler-inlined static functions (such as static inlines in mm/*.h or include/linux/*.h) lack
  distinct symbol addresses in vmlinux and cannot be targeted directly by symbol coverage filters.
  If the changes are primarily in static inline helpers, identify non-static, feature-specific caller
  functions in .c files that exercise them (avoiding ubiquitous lifecycle wrappers).

================================================================================
5. IDENTIFYING EnableConfigs
================================================================================
Identify any specific CONFIG_ options required to properly compile and reach the modified code:
- Inspect Kconfig files and #ifdef guards; do not make assumptions.
- Check "depends on" lines in Kconfig to include any non-standard parent subsystem configs needed.
- Strip any '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.

Target architecture: amd64

For your convenience, here is the diff of the changes:
commit 0b4dc9b2876ab4cea9413c2d84ace96714063bd3
Author: syz-cluster <triage@syzkaller.com>
Date:   Thu Sep 10 04:49:18 2026 +0000

    syz-cluster: applied patch under review

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 72a3f5998dd27..ee41b7386f752 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -800,6 +800,39 @@ static int dynptr_ref_cnt(struct bpf_verifier_env *env, int v_parent_id)
 	return ref_cnt;
 }
 
+static void reparent_dynptr_slices_on_func_exit(struct bpf_verifier_env *env,
+						struct bpf_func_state *callee)
+{
+	struct bpf_verifier_state *vstate = env->cur_state;
+	struct bpf_func_state *state;
+	struct bpf_reg_state *reg;
+	int i;
+
+	for (i = 0; i < callee->allocated_stack / BPF_REG_SIZE; i++) {
+		struct bpf_stack_state *slot = &callee->stack[i];
+		struct bpf_reg_state *dynptr = &slot->spilled_ptr;
+
+		if (slot->slot_type[0] != STACK_DYNPTR ||
+		    !dynptr->dynptr.first_slot ||
+		    !dynptr->parent_id)
+			continue;
+
+		/*
+		 * A callee can spill a slice derived from its local dynptr into
+		 * the caller's stack. The slice then outlives the dynptr id that
+		 * links it to the rest of the object tree. Preserve that link by
+		 * making escaped slices children of the dynptr's parent before
+		 * the callee frame is freed.
+		 */
+		bpf_for_each_reg_in_vstate(vstate, state, reg, ({
+			if (state == callee || reg->parent_id != dynptr->id ||
+			    base_type(reg->type) != PTR_TO_MEM)
+				continue;
+			reg->parent_id = dynptr->parent_id;
+		}));
+	}
+}
+
 static int destroy_if_dynptr_stack_slot(struct bpf_verifier_env *env,
 				        struct bpf_func_state *state, int spi)
 {
@@ -10399,6 +10432,7 @@ static int prepare_func_exit(struct bpf_verifier_env *env, int *insn_idx)
 		print_verifier_state(env, state, caller->frameno, true);
 	}
 	account_processed_insns(env, callee, caller);
+	reparent_dynptr_slices_on_func_exit(env, callee);
 	/* clear everything in the callee. In case of exceptional exits using
 	 * bpf_throw, this will be done by copy_verifier_state for extra frames. */
 	free_func_state(callee);
diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_qdisc.c b/tools/testing/selftests/bpf/prog_tests/bpf_qdisc.c
index 6dbd1487343c0..122ecb7e98e2a 100644
--- a/tools/testing/selftests/bpf/prog_tests/bpf_qdisc.c
+++ b/tools/testing/selftests/bpf/prog_tests/bpf_qdisc.c
@@ -11,6 +11,7 @@
 #include "bpf_qdisc_fail__invalid_dynptr.skel.h"
 #include "bpf_qdisc_fail__invalid_dynptr_slice.skel.h"
 #include "bpf_qdisc_fail__invalid_dynptr_cross_frame.skel.h"
+#include "bpf_qdisc_fail__invalid_dynptr_returned_slice.skel.h"
 #include "bpf_qdisc_fail__untrusted_write.skel.h"
 #include "bpf_qdisc_dynptr_use_after_invalidate_clone.skel.h"
 
@@ -230,6 +231,7 @@ void test_ns_bpf_qdisc(void)
 		test_incompl_ops();
 	RUN_TESTS(bpf_qdisc_fail__invalid_dynptr);
 	RUN_TESTS(bpf_qdisc_fail__invalid_dynptr_cross_frame);
+	RUN_TESTS(bpf_qdisc_fail__invalid_dynptr_returned_slice);
 	RUN_TESTS(bpf_qdisc_fail__invalid_dynptr_slice);
 	RUN_TESTS(bpf_qdisc_fail__untrusted_write);
 	RUN_TESTS(bpf_qdisc_dynptr_use_after_invalidate_clone);
diff --git a/tools/testing/selftests/bpf/progs/bpf_qdisc_fail__invalid_dynptr_returned_slice.c b/tools/testing/selftests/bpf/progs/bpf_qdisc_fail__invalid_dynptr_returned_slice.c
new file mode 100644
index 0000000000000..940aba7d8abfe
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/bpf_qdisc_fail__invalid_dynptr_returned_slice.c
@@ -0,0 +1,76 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <vmlinux.h>
+#include "bpf_experimental.h"
+#include "bpf_qdisc_common.h"
+#include "bpf_misc.h"
+
+char _license[] SEC("license") = "GPL";
+
+int proto;
+
+static __noinline struct ethhdr *slice_in_subprog(struct sk_buff *skb)
+{
+	struct bpf_dynptr ptr;
+
+	bpf_dynptr_from_skb((struct __sk_buff *)skb, 0, &ptr);
+	return bpf_dynptr_slice(&ptr, 0, NULL, sizeof(struct ethhdr));
+}
+
+SEC("struct_ops")
+__failure __msg("invalid mem access 'scalar'")
+int BPF_PROG(invalid_dynptr_returned_slice, struct sk_buff *skb,
+	     struct Qdisc *sch, struct bpf_sk_buff_ptr *to_free)
+{
+	struct ethhdr *hdr;
+
+	hdr = slice_in_subprog(skb);
+	if (!hdr) {
+		bpf_qdisc_skb_drop(skb, to_free);
+		return NET_XMIT_DROP;
+	}
+
+	bpf_qdisc_skb_drop(skb, to_free);
+
+	/* this should fail */
+	proto = hdr->h_proto;
+
+	return NET_XMIT_DROP;
+}
+
+SEC("struct_ops")
+__auxiliary
+struct sk_buff *BPF_PROG(bpf_qdisc_test_dequeue, struct Qdisc *sch)
+{
+	return NULL;
+}
+
+SEC("struct_ops")
+__auxiliary
+int BPF_PROG(bpf_qdisc_test_init, struct Qdisc *sch, struct nlattr *opt,
+	     struct netlink_ext_ack *extack)
+{
+	return 0;
+}
+
+SEC("struct_ops")
+__auxiliary
+void BPF_PROG(bpf_qdisc_test_reset, struct Qdisc *sch)
+{
+}
+
+SEC("struct_ops")
+__auxiliary
+void BPF_PROG(bpf_qdisc_test_destroy, struct Qdisc *sch)
+{
+}
+
+SEC(".struct_ops")
+struct Qdisc_ops test = {
+	.enqueue   = (void *)invalid_dynptr_returned_slice,
+	.dequeue   = (void *)bpf_qdisc_test_dequeue,
+	.init      = (void *)bpf_qdisc_test_init,
+	.reset     = (void *)bpf_qdisc_test_reset,
+	.destroy   = (void *)bpf_qdisc_test_destroy,
+	.id        = "bpf_qdisc_test",
+};
diff --git a/tools/testing/selftests/bpf/progs/dynptr_fail.c b/tools/testing/selftests/bpf/progs/dynptr_fail.c
index 1cd61d72c166f..92f9f9ea05321 100644
--- a/tools/testing/selftests/bpf/progs/dynptr_fail.c
+++ b/tools/testing/selftests/bpf/progs/dynptr_fail.c
@@ -1892,6 +1892,55 @@ int clone_invalidate4(void *ctx)
 	return 0;
 }
 
+static __noinline void clone_slice_in_subprog(struct bpf_dynptr *ptr, int **data)
+{
+	struct bpf_dynptr clone;
+
+	bpf_dynptr_clone(ptr, &clone);
+	*data = bpf_dynptr_data(&clone, 0, sizeof(val));
+}
+
+/*
+ * A slice that escapes the clone's call frame remains valid while the
+ * shared ringbuf reservation is live.
+ */
+SEC("?raw_tp")
+__success
+int clone_slice_returned_frame_valid(void *ctx)
+{
+	struct bpf_dynptr ptr;
+	int *data = NULL;
+
+	bpf_ringbuf_reserve_dynptr(&ringbuf, val, 0, &ptr);
+	clone_slice_in_subprog(&ptr, &data);
+	if (data)
+		*data = 123;
+	bpf_ringbuf_submit_dynptr(&ptr, 0);
+
+	return 0;
+}
+
+/*
+ * Releasing the shared reservation must invalidate a slice that escaped
+ * from a clone's call frame.
+ */
+SEC("?raw_tp")
+__failure __msg("invalid mem access 'scalar'")
+int clone_slice_returned_frame_invalid(void *ctx)
+{
+	struct bpf_dynptr ptr;
+	int *data = NULL;
+
+	bpf_ringbuf_reserve_dynptr(&ringbuf, val, 0, &ptr);
+	clone_slice_in_subprog(&ptr, &data);
+	bpf_ringbuf_submit_dynptr(&ptr, 0);
+	if (data)
+		/* this should fail */
+		*data = 123;
+
+	return 0;
+}
+
 /* Invalidating a dynptr should invalidate any data slices
  * of its parent
  */

gemini-3.7-flash

null

null

							input: 5446
							output: 38
							thoughts: 231
						

**Analyzing a Linux Kernel Patch for Syzkaller Fuzzing**

Okay, so I need to assess this Linux kernel patch series for its fuzzing potential with syzkaller. The user is asking the right questions – is this worth our time, what configs do we need to focus on, and what symbols are most relevant? It's all about triage here – standard Linux kernel maintenance, QA, and security engineering. This is a completely benign and defensive operation, so no worries there.

Let's dive into the patch itself. It seems the core modification is within `kernel/bpf/verifier.c` and its associated selftests in `tools/testing/selftests/bpf/...`. Specifically, there's a new function, `reparent_dynptr_slices_on_func_exit`, being introduced within `verifier.c`, and it's being called from `prepare_func_exit`. Okay, `verifier.c`... that's interesting. The BPF verifier is always a good target.

Now, I'll use `grepper` (or, if I have to, `read-file`) to get the surrounding context of `verifier.c`. I need to figure out what kernel configurations are crucial for enabling this functionality. Knowing the dependencies on other kernel subsystems will be key to getting a full picture. I need to identify which functions are *most* likely to be triggered by fuzzing. Are there any critical data structures or operations related to `dynptr` (dynamic pointer) that are now in play? My goal is to quickly pinpoint the most interesting symbols and potential crash surfaces for syzkaller. Let's see what we can find.

{
  "Expression": "reparent_dynptr_slices_on_func_exit",
  "PathPrefix": "kernel/bpf/"
}

{
  "Output": "kernel/bpf/verifier.c=784=static int dynptr_ref_cnt(struct bpf_verifier_env *env, int v_parent_id)\n--\nkernel/bpf/verifier.c-802-\nkernel/bpf/verifier.c:803:static void reparent_dynptr_slices_on_func_exit(struct bpf_verifier_env *env,\nkernel/bpf/verifier.c-804-\t\t\t\t\t\tstruct bpf_func_state *callee)\n--\nkernel/bpf/verifier.c=10367=static int prepare_func_exit(struct bpf_verifier_env *env, int *insn_idx)\n--\nkernel/bpf/verifier.c-10434-\taccount_processed_insns(env, callee, caller);\nkernel/bpf/verifier.c:10435:\treparent_dynptr_slices_on_func_exit(env, callee);\nkernel/bpf/verifier.c-10436-\t/* clear everything in the callee. In case of exceptional exits using\n"
}

gemini-3.7-flash

null

null

							input: 6346
							output: 36
							thoughts: 66
						

**Examining Kernel BPF Verifier Function Exit Handling**

Okay, time to dive into this. I need to refresh my memory on how the BPF verifier handles function exits, particularly with respect to dynamic pointer slices. Let's start by looking at `prepare_func_exit` and `reparent_dynptr_slices_on_func_exit` functions within `kernel/bpf/verifier.c`. These are the key functions handling what happens when a BPF function is exiting, and they're likely where the logic for pointer management resides. I'll focus my attention around line 800 in `kernel/bpf/verifier.c` and take a good look at the code block in that area, and the related code, to understand the current implementation. I need to grasp how the dynamic pointers and slices are being managed, especially to figure out the bug that has been reported. Hopefully, by understanding these key routines, I can identify the root cause of the issue and pinpoint a solution.

{
  "File": "kernel/bpf/verifier.c",
  "FirstLine": 800,
  "LineCount": 40
}

{
  "Contents": " 800:\t\treturn ref_cnt;\n 801:\t}\n 802:\t\n 803:\tstatic void reparent_dynptr_slices_on_func_exit(struct bpf_verifier_env *env,\n 804:\t\t\t\t\t\t\tstruct bpf_func_state *callee)\n 805:\t{\n 806:\t\tstruct bpf_verifier_state *vstate = env-\u003ecur_state;\n 807:\t\tstruct bpf_func_state *state;\n 808:\t\tstruct bpf_reg_state *reg;\n 809:\t\tint i;\n 810:\t\n 811:\t\tfor (i = 0; i \u003c callee-\u003eallocated_stack / BPF_REG_SIZE; i++) {\n 812:\t\t\tstruct bpf_stack_state *slot = \u0026callee-\u003estack[i];\n 813:\t\t\tstruct bpf_reg_state *dynptr = \u0026slot-\u003espilled_ptr;\n 814:\t\n 815:\t\t\tif (slot-\u003eslot_type[0] != STACK_DYNPTR ||\n 816:\t\t\t    !dynptr-\u003edynptr.first_slot ||\n 817:\t\t\t    !dynptr-\u003eparent_id)\n 818:\t\t\t\tcontinue;\n 819:\t\n 820:\t\t\t/*\n 821:\t\t\t * A callee can spill a slice derived from its local dynptr into\n 822:\t\t\t * the caller's stack. The slice then outlives the dynptr id that\n 823:\t\t\t * links it to the rest of the object tree. Preserve that link by\n 824:\t\t\t * making escaped slices children of the dynptr's parent before\n 825:\t\t\t * the callee frame is freed.\n 826:\t\t\t */\n 827:\t\t\tbpf_for_each_reg_in_vstate(vstate, state, reg, ({\n 828:\t\t\t\tif (state == callee || reg-\u003eparent_id != dynptr-\u003eid ||\n 829:\t\t\t\t    base_type(reg-\u003etype) != PTR_TO_MEM)\n 830:\t\t\t\t\tcontinue;\n 831:\t\t\t\treg-\u003eparent_id = dynptr-\u003eparent_id;\n 832:\t\t\t}));\n 833:\t\t}\n 834:\t}\n 835:\t\n 836:\tstatic int destroy_if_dynptr_stack_slot(struct bpf_verifier_env *env,\n 837:\t\t\t\t\t        struct bpf_func_state *state, int spi)\n 838:\t{\n 839:\t\tint err = 0;\n"
}

gemini-3.7-flash

null

null

							input: 7329
							output: 38
							thoughts: 20
						

Here's a summary of my thought process, as requested:

**Navigating Complex Code: A Focused Investigation**

Okay, so I'm digging into this codebase, and I need to pinpoint the issue. My mental map is leading me to `prepare_func_exit`. Let's zero in on that section, around line 10400. That's where I anticipate the relevant logic resides. I'm focusing my attention there because I have a hunch related to the failure mode and that particular function is in my target zone for the kind of problem I'm trying to solve.

{
  "File": "kernel/bpf/verifier.c",
  "FirstLine": 10420,
  "LineCount": 30
}

{
  "Contents": "10420:\t\t * converges is_state_visited() would prune that visit eventually.\n10421:\t\t */\n10422:\t\tin_callback_fn = callee-\u003ein_callback_fn;\n10423:\t\tif (in_callback_fn)\n10424:\t\t\t*insn_idx = callee-\u003ecallsite;\n10425:\t\telse\n10426:\t\t\t*insn_idx = callee-\u003ecallsite + 1;\n10427:\t\n10428:\t\tif (env-\u003elog.level \u0026 BPF_LOG_LEVEL) {\n10429:\t\t\tverbose(env, \"returning from callee:\\n\");\n10430:\t\t\tprint_verifier_state(env, state, callee-\u003eframeno, true);\n10431:\t\t\tverbose(env, \"to caller at %d:\\n\", *insn_idx);\n10432:\t\t\tprint_verifier_state(env, state, caller-\u003eframeno, true);\n10433:\t\t}\n10434:\t\taccount_processed_insns(env, callee, caller);\n10435:\t\treparent_dynptr_slices_on_func_exit(env, callee);\n10436:\t\t/* clear everything in the callee. In case of exceptional exits using\n10437:\t\t * bpf_throw, this will be done by copy_verifier_state for extra frames. */\n10438:\t\tfree_func_state(callee);\n10439:\t\tstate-\u003eframe[state-\u003ecurframe--] = NULL;\n10440:\t\tinvalidate_outgoing_stack_args(env, caller);\n10441:\t\n10442:\t\t/* for callbacks widen imprecise scalars to make programs like below verify:\n10443:\t\t *\n10444:\t\t *   struct ctx { int i; }\n10445:\t\t *   void cb(int idx, struct ctx *ctx) { ctx-\u003ei++; ... }\n10446:\t\t *   ...\n10447:\t\t *   struct ctx = { .i = 0; }\n10448:\t\t *   bpf_loop(100, cb, \u0026ctx, 0);\n10449:\t\t *\n"
}

gemini-3.7-flash

null

null

							input: 8096
							output: 30
							thoughts: 592
						

**Analyzing the BPF Verifier Patch for Fuzzing Potential**

Okay, let's break this down. First, is this code even reachable? Yep, it's right there in `kernel/bpf/verifier.c`. The BPF verifier is a critical part of the Linux kernel, accessible through the `bpf()` syscall with `BPF_PROG_LOAD`, which means userspace can trigger it. It's easily fuzzed, too, thanks to tools like syzkaller. Good start.

Now, what's this patch actually *doing*? It's handling the reparenting of dynamic pointer (dynptr) slices when a BPF function returns. Specifically, if a called function (subprogram, callee) spills a slice that came from a local dynptr into the caller's stack or registers, that slice's lifetime extends beyond the dynptr ID. The patch is modifying the verifier's state tracking logic in `prepare_func_exit` to correctly reparent those slices to the correct dynptr's parent.

Is it worth fuzzing? Absolutely. Any change to the core BPF verifier logic is high-priority for fuzzing. The verifier is a key subsystem, so modifications here are prime targets.

Okay, now for `FocusSymbols`. What are the key functions to focus on? Let's see... Initially, I thought `bpf_check` should be listed, as it's the main entry point for the verifier, but that is the main entrypoint, while `prepare_func_exit` and `reparent_dynptr_slices_on_func_exit` are more specific to this change.

I need to apply the "EXTRACTING FocusSymbols" methodology I keep at hand:

*   Avoid generic, ubiquitous functions.
*   Target specific feature logic and entrypoints.

`reparent_dynptr_slices_on_func_exit` is the new static function added. `prepare_func_exit` calls this function. `prepare_func_exit` is called by several functions.

In `kernel/bpf/verifier.c`:

*   `static void reparent_dynptr_slices_on_func_exit(struct bpf_verifier_env *env, struct bpf_func_state *callee)`
*   `static int prepare_func_exit(...)`

I'll need to figure out which functions call `prepare_func_exit`. I'm confident that I will know which functions to fuzz, given that the BPF verifier is a major subsystem.

{
  "Expression": "prepare_func_exit",
  "PathPrefix": "kernel/bpf/"
}

{
  "Output": "kernel/bpf/verifier.c=10359=static bool retval_range_within(struct bpf_retval_range range, const struct bpf_reg_state *reg)\n--\nkernel/bpf/verifier.c-10366-\nkernel/bpf/verifier.c:10367:static int prepare_func_exit(struct bpf_verifier_env *env, int *insn_idx)\nkernel/bpf/verifier.c-10368-{\n--\nkernel/bpf/verifier.c=10847=static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn,\n--\nkernel/bpf/verifier.c-11349-\t\t\t * frame. A callback frame cannot be left that way because\nkernel/bpf/verifier.c:11350:\t\t\t * prepare_func_exit() would apply its return contract to the\nkernel/bpf/verifier.c-11351-\t\t\t * unknown R0 synthesized below. Stack-depth validation rejects\n--\nkernel/bpf/verifier.c-11363-\t\t\tmark_reg_unknown(env, regs, BPF_REG_0);\nkernel/bpf/verifier.c:11364:\t\t\terr = prepare_func_exit(env, \u0026env-\u003einsn_idx);\nkernel/bpf/verifier.c-11365-\t\t\tif (err)\n--\nkernel/bpf/verifier.c=17322=static int check_ld_abs(struct bpf_verifier_env *env, struct bpf_insn *insn)\n--\nkernel/bpf/verifier.c-17402-\t\tmark_reg_known_zero(env, regs, BPF_REG_0);\nkernel/bpf/verifier.c:17403:\t\terr = prepare_func_exit(env, \u0026env-\u003einsn_idx);\nkernel/bpf/verifier.c-17404-\t\tif (err)\n--\nkernel/bpf/verifier.c=18109=static int process_bpf_exit_full(struct bpf_verifier_env *env,\n--\nkernel/bpf/verifier.c-18115-\t/* We must do check_reference_leak here before\nkernel/bpf/verifier.c:18116:\t * prepare_func_exit to handle the case when\nkernel/bpf/verifier.c-18117-\t * state-\u003ecurframe \u003e 0, it may be a callback function,\n--\nkernel/bpf/verifier.c-18127-\nkernel/bpf/verifier.c:18128:\t/* The side effect of the prepare_func_exit which is\nkernel/bpf/verifier.c-18129-\t * being skipped is that it frees bpf_func_state.\n--\nkernel/bpf/verifier.c-18141-\t\t/* exit from nested function */\nkernel/bpf/verifier.c:18142:\t\terr = prepare_func_exit(env, \u0026env-\u003einsn_idx);\nkernel/bpf/verifier.c-18143-\t\tif (err)\n"
}

gemini-3.7-flash

null

null

							input: 10061
							output: 28
							thoughts: 49
						

Okay, let's dive into this. Here's how I'd approach this task, walking through my thought process:

**Verifying BPF Verifier Configuration**

Right, so I'm looking into the kernel's BPF verifier setup. First things first, I need to pinpoint the essential Kconfig options that govern the compilation of `kernel/bpf/verifier.c`. This is foundational – ensuring the verifier itself is *enabled* and configured correctly is the bedrock of anything BPF-related. Where are these settings likely to be defined? Well, I'd immediately head to the obvious places.

I'd need to examine both the `kernel/bpf/Makefile` and either `init/Kconfig` or `kernel/bpf/Kconfig`. `Makefile` to see the compilation dependencies, and the `Kconfig` files would contain the actual configuration options. From those I can determine any dependencies, whether the build rules are active, and what the dependencies might be. I need to make sure I am examining the relevant ones and that I haven't missed any. I have to make sure that the verifier is enabled for the build, otherwise, I won't have anything to work with.

{
  "Expression": "verifier\\.o",
  "PathPrefix": "kernel/bpf/"
}

{
  "Output": "kernel/bpf/Makefile=7=CFLAGS_core.o += -Wno-override-init $(cflags-nogcse-yy)\nkernel/bpf/Makefile-8-\nkernel/bpf/Makefile:9:obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o inode.o helpers.o tnum.o cnum.o log.o token.o liveness.o const_fold.o diagnostics.o\nkernel/bpf/Makefile-10-obj-$(CONFIG_BPF_SYSCALL) += bpf_iter.o map_iter.o task_iter.o prog_iter.o link_iter.o\n"
}

gemini-3.7-flash

null

null

							input: 10562
							output: 29
							thoughts: 29
						

Here's my take on the thought process, as if it were my own:

**Investigating BPF Syscall Configuration**

Alright, I need to pinpoint where the `BPF_SYSCALL` configuration option is defined. Given my familiarity with the kernel build system, the most logical places to start looking are the primary configuration files. I'll begin by checking `init/Kconfig` – it often holds fundamental settings related to kernel features. If it's not there, the next logical location would be the core BPF implementation directory itself, specifically `kernel/bpf/Kconfig`. This is where I would expect anything related to BPF's system call interface to reside. I need to figure out how it is implemented. I'm going to look in those two places.

no matches

{
  "Expression": "config BPF_SYSCALL",
  "PathPrefix": "init/"
}

{
  "error": "no matches"
}

gemini-3.7-flash

null

null

							input: 10800
							output: 21
							thoughts: 19
						

Here's my thought process, as requested:

**Navigating the Kernel Configuration Landscape**

Okay, so I need to figure out where `BPF_SYSCALL` is defined in the Kconfig files. This is a common task, especially when dealing with BPF-related configurations, and I need to be efficient. I’ll start by doing a quick search within the Kconfig files. I know I can use my tools to search within the kernel source. Given my experience, I'm going to start with a grep-like search through the Kconfig files to see if the symbol has been defined. Then I will need to look at the config options to see what the symbol does. My goal is to understand its dependencies, its implications, and how it relates to the overall BPF feature set. This information is critical for any future modifications or troubleshooting related to BPF syscalls. Time to dig in!

{
  "Expression": "config BPF_SYSCALL"
}

{
  "Output": "kernel/bpf/Kconfig=25=menu \"BPF subsystem\"\nkernel/bpf/Kconfig-26-\nkernel/bpf/Kconfig:27:config BPF_SYSCALL\nkernel/bpf/Kconfig-28-\tbool \"Enable bpf() system call\"\n"
}

gemini-3.7-flash

null

null

							input: 11113
							output: 34
							thoughts: 23
						

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

**Diving into the BPF Configuration**

Okay, so I need to understand the configuration dependencies for this BPF feature. My first instinct is to dive into the `Kconfig` file within the `kernel/bpf/` directory. That's the go-to place for understanding how a feature is enabled and what else it depends on. I'll zero in on line 27 – that seems like a reasonable starting point, often the initial entry for a feature definition. Hopefully, that will give me a clear picture of any prerequisites or other configurations that need to be in place before this BPF component can be activated. Time to see what the Kconfig has to say!

{
  "File": "kernel/bpf/Kconfig",
  "FirstLine": 25,
  "LineCount": 25
}

{
  "Contents": "  25:\tmenu \"BPF subsystem\"\n  26:\t\n  27:\tconfig BPF_SYSCALL\n  28:\t\tbool \"Enable bpf() system call\"\n  29:\t\tselect BPF\n  30:\t\tselect IRQ_WORK\n  31:\t\tselect NEED_TASKS_RCU\n  32:\t\tselect TASKS_TRACE_RCU\n  33:\t\tselect BINARY_PRINTF\n  34:\t\tselect NET_SOCK_MSG if NET\n  35:\t\tselect NET_XGRESS if NET\n  36:\t\tselect PAGE_POOL if NET\n  37:\t\tdefault n\n  38:\t\thelp\n  39:\t\t  Enable the bpf() system call that allows to manipulate BPF programs\n  40:\t\t  and maps via file descriptors.\n  41:\t\n  42:\tconfig BPF_JIT\n  43:\t\tbool \"Enable BPF Just In Time compiler\"\n  44:\t\tdepends on BPF\n  45:\t\tdepends on HAVE_CBPF_JIT || HAVE_EBPF_JIT\n  46:\t\tselect EXECMEM\n  47:\t\thelp\n  48:\t\t  BPF programs are normally handled by a BPF interpreter. This option\n  49:\t\t  allows the kernel to generate native code when a program is loaded\n"
}

gemini-3.7-flash

null

null

							input: 11661
							output: 31
							thoughts: 142
						

**My BPF Verification Thoughts**

Okay, so `CONFIG_BPF_SYSCALL` is the crucial configuration option; it's the one that ultimately brings in `kernel/bpf/verifier.o`. I need to make sure I haven't missed any other config dependencies, although I strongly suspect `BPF_SYSCALL` is the only relevant piece here. The menu structure in the kernel config ("BPF subsystem") is pretty straightforward, and `BPF_SYSCALL` seems to be standalone. No dependencies, good.

Now, to make sure I haven't forgotten anything else I want to double-check my mental list of key symbols for my work: `reparent_dynptr_slices_on_func_exit`, `prepare_func_exit`, and then either `process_bpf_exit_full` or `bpf_check` - I need to keep those in mind as I dive in.

Right, let's now drill down into `bpf_check`. It's time to dig into `verifier.c` and see what's what.

{
  "Expression": "int bpf_check\\(",
  "PathPrefix": "kernel/bpf/"
}

{
  "Output": "kernel/bpf/verifier.c=21049=static int bpf_prog_verify_signature(struct bpf_verifier_env *env,\n--\nkernel/bpf/verifier.c-21165-\nkernel/bpf/verifier.c:21166:int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr,\nkernel/bpf/verifier.c-21167-\t      struct bpf_log_attr *attr_log)\n"
}

gemini-3.7-flash

null

null

							input: 12212
							output: 126
							thoughts: 357
						

**My Assessment of the BPF Verifier Change**

Okay, let's break this down. First, I need to understand the scope of the change, so I'll start by checking `bpf_for_each_reg_in_vstate` in `verifier.c` to see if there are any other related modifications in that area. Then, I should also look at the `dynptr` functions, particularly `dynptr_ref_cnt`, also within `verifier.c`. My primary concerns right now are `reparent_dynptr_slices_on_func_exit` and `prepare_func_exit` because they are explicitly flagged as directly affected.

Now, let's review the parameters for `set-results`. The key thing is that we've set `WorthFuzzing` to `true`, which is appropriate given the nature of the change. The `Reasoning` section gives a good overview: this patch alters BPF verifier logic within the kernel, specifically by introducing `reparent_dynptr_slices_on_func_exit` during `prepare_func_exit`. The point is, this reparents `dynptr` slices upon function exit to maintain lineage tracking across caller frames. This touches core verifier code used by `bpf(BPF_PROG_LOAD, ...)` which is a strong indicator for fuzzing.

The `FocusSymbols` are precise: `reparent_dynptr_slices_on_func_exit` and `prepare_func_exit`, which is perfect. This helps us direct our fuzzing efforts to the relevant code. And we're enabling `BPF_SYSCALL` as the `EnableConfigs`.

Finally, just a sanity check: everything looks in order. `WorthFuzzing` is set as expected, the `FocusSymbols` are specific to this patch, and the `EnableConfigs` are sensible. The `Reasoning` is concise and on point.

Okay, let's submit the `set-results` command.

{
  "EnableConfigs": [
    "BPF_SYSCALL"
  ],
  "FocusSymbols": [
    "reparent_dynptr_slices_on_func_exit",
    "prepare_func_exit"
  ],
  "Reasoning": "The patch introduces reparent_dynptr_slices_on_func_exit() in kernel/bpf/verifier.c, called from prepare_func_exit() to update dynptr lineage tracking when callee frames return. This modifies core BPF verifier logic reachable via BPF program loading syscalls.",
  "WorthFuzzing": true
}

{
  "EnableConfigs": [
    "BPF_SYSCALL"
  ],
  "FocusSymbols": [
    "reparent_dynptr_slices_on_func_exit",
    "prepare_func_exit"
  ],
  "Reasoning": "The patch introduces reparent_dynptr_slices_on_func_exit() in kernel/bpf/verifier.c, called from prepare_func_exit() to update dynptr lineage tracking when callee frames return. This modifies core BPF verifier logic reachable via BPF program loading syscalls.",
  "WorthFuzzing": true
}

{
  "WorthFuzzing": true
}

null

core

null

{
  "KMSANReasoning": "The patch modifies the BPF verifier's `prepare_func_exit()` logic by adding `reparent_dynptr_slices_on_func_exit()`. This ensures that dynptr slices escaping a subprogram call frame have their `parent_id` updated to point to the dynptr's parent, properly invalidating slices when the parent dynptr/buffer is destroyed in the caller.\n\nThis fix prevents Use-After-Free (UAF) / dangling pointer dereferences in BPF programs. Such runtime memory safety violations are caught by KASAN. The patch does not introduce or expose uninitialized memory reads, uninitialized struct fields, or kernel-to-user info-leaks. Therefore, KMSAN is not needed.",
  "NeedsKMSAN": false
}

You are an expert Linux kernel security engineer specializing in kernel memory
error detectors (KASAN and KMSAN). Your job is to review the provided patch series and
determine if the code changes justify spawning a dedicated KMSAN (KernelMemorySanitizer)
fuzzing session in addition to standard KASAN fuzzing.

CRITICAL DISTINCTION BETWEEN KASAN AND KMSAN:
- Standard KASAN kernel builds (upstream-apparmor-kasan.config) already enable
  a comprehensive suite of debugging tools and sanitizers, including KASAN
  (out-of-bounds accesses, use-after-free, double free, invalid free), LOCKDEP
  (locking bugs and deadlocks), UB-sanitizers, and memory corruption checks.
- KMSAN (KernelMemorySanitizer) detects reads of UNINITIALIZED memory (stack, heap,
  or page allocations) and kernel-to-user memory info-leaks.

Rule: THERE IS NO SENSE IN RUNNING A KMSAN SESSION IF A BUG CAN BE CAUGHT BY KASAN,
LOCKDEP, OR OTHER STANDARD BUG DETECTORS.
A dedicated KMSAN fuzzing session incurs significant resource costs. You must ONLY
set NeedsKMSAN=true if the code changes introduce or expose UNINITIALIZED MEMORY risks
that are detected ONLY by KMSAN.

Look holistically at the patch series and surrounding code. Even if no direct
uninitialized field accesses or new buffer allocations are added in the diff itself,
a patch may alter control flow, bounds checking, or data length calculations in ways
that change how the rest of the code operates on existing buffers (e.g. allowing
uninitialized stack/heap memory to be read, copied to user space, or used in control
flow). Do not hesitate to use your code access tools to inspect the surrounding code,
called functions, and callers.

Set NeedsKMSAN=true ONLY IF the patch introduces or modifies:
1. Kernel structures sent to user space (via copy_to_user, put_user, netlink skb
   attributes, ioctl output arguments, socket options, or BPF buffers) where fields
   or structure padding might not be fully initialized/zeroed.
2. Conditional logic or branching that depends on potentially uninitialized variables
   or struct fields.
3. Allocation or initialization of complex data structures where uninitialized fields
   could be read later in reachable code paths.
4. Bounds checks, lengths, or logic in a way that allows surrounding code to access
   uninitialized bytes of existing buffers.

Set NeedsKMSAN=false IF:
- The code changes primarily risk out-of-bounds access, array overflows, NULL pointer
  dereferences, locking deadlocks, or use-after-free bugs (these are already caught
  by KASAN, LOCKDEP, or standard bug detectors).
- All stack/heap structures touched or introduced by the patch are fully zeroed
  or initialized (e.g. using = {0}, memset, kzalloc) before being read or copied.
- The patch does not introduce any risk of uninitialized memory usage or info-leaks.

Use your code access tools to inspect the surrounding code if necessary, then provide
detailed KMSANReasoning contrasting KASAN vs KMSAN applicability for this patch.
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.

Target architecture: amd64

For your convenience, here is the diff of the changes:
commit 0b4dc9b2876ab4cea9413c2d84ace96714063bd3
Author: syz-cluster <triage@syzkaller.com>
Date:   Thu Sep 10 04:49:18 2026 +0000

    syz-cluster: applied patch under review

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 72a3f5998dd27..ee41b7386f752 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -800,6 +800,39 @@ static int dynptr_ref_cnt(struct bpf_verifier_env *env, int v_parent_id)
 	return ref_cnt;
 }
 
+static void reparent_dynptr_slices_on_func_exit(struct bpf_verifier_env *env,
+						struct bpf_func_state *callee)
+{
+	struct bpf_verifier_state *vstate = env->cur_state;
+	struct bpf_func_state *state;
+	struct bpf_reg_state *reg;
+	int i;
+
+	for (i = 0; i < callee->allocated_stack / BPF_REG_SIZE; i++) {
+		struct bpf_stack_state *slot = &callee->stack[i];
+		struct bpf_reg_state *dynptr = &slot->spilled_ptr;
+
+		if (slot->slot_type[0] != STACK_DYNPTR ||
+		    !dynptr->dynptr.first_slot ||
+		    !dynptr->parent_id)
+			continue;
+
+		/*
+		 * A callee can spill a slice derived from its local dynptr into
+		 * the caller's stack. The slice then outlives the dynptr id that
+		 * links it to the rest of the object tree. Preserve that link by
+		 * making escaped slices children of the dynptr's parent before
+		 * the callee frame is freed.
+		 */
+		bpf_for_each_reg_in_vstate(vstate, state, reg, ({
+			if (state == callee || reg->parent_id != dynptr->id ||
+			    base_type(reg->type) != PTR_TO_MEM)
+				continue;
+			reg->parent_id = dynptr->parent_id;
+		}));
+	}
+}
+
 static int destroy_if_dynptr_stack_slot(struct bpf_verifier_env *env,
 				        struct bpf_func_state *state, int spi)
 {
@@ -10399,6 +10432,7 @@ static int prepare_func_exit(struct bpf_verifier_env *env, int *insn_idx)
 		print_verifier_state(env, state, caller->frameno, true);
 	}
 	account_processed_insns(env, callee, caller);
+	reparent_dynptr_slices_on_func_exit(env, callee);
 	/* clear everything in the callee. In case of exceptional exits using
 	 * bpf_throw, this will be done by copy_verifier_state for extra frames. */
 	free_func_state(callee);
diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_qdisc.c b/tools/testing/selftests/bpf/prog_tests/bpf_qdisc.c
index 6dbd1487343c0..122ecb7e98e2a 100644
--- a/tools/testing/selftests/bpf/prog_tests/bpf_qdisc.c
+++ b/tools/testing/selftests/bpf/prog_tests/bpf_qdisc.c
@@ -11,6 +11,7 @@
 #include "bpf_qdisc_fail__invalid_dynptr.skel.h"
 #include "bpf_qdisc_fail__invalid_dynptr_slice.skel.h"
 #include "bpf_qdisc_fail__invalid_dynptr_cross_frame.skel.h"
+#include "bpf_qdisc_fail__invalid_dynptr_returned_slice.skel.h"
 #include "bpf_qdisc_fail__untrusted_write.skel.h"
 #include "bpf_qdisc_dynptr_use_after_invalidate_clone.skel.h"
 
@@ -230,6 +231,7 @@ void test_ns_bpf_qdisc(void)
 		test_incompl_ops();
 	RUN_TESTS(bpf_qdisc_fail__invalid_dynptr);
 	RUN_TESTS(bpf_qdisc_fail__invalid_dynptr_cross_frame);
+	RUN_TESTS(bpf_qdisc_fail__invalid_dynptr_returned_slice);
 	RUN_TESTS(bpf_qdisc_fail__invalid_dynptr_slice);
 	RUN_TESTS(bpf_qdisc_fail__untrusted_write);
 	RUN_TESTS(bpf_qdisc_dynptr_use_after_invalidate_clone);
diff --git a/tools/testing/selftests/bpf/progs/bpf_qdisc_fail__invalid_dynptr_returned_slice.c b/tools/testing/selftests/bpf/progs/bpf_qdisc_fail__invalid_dynptr_returned_slice.c
new file mode 100644
index 0000000000000..940aba7d8abfe
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/bpf_qdisc_fail__invalid_dynptr_returned_slice.c
@@ -0,0 +1,76 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <vmlinux.h>
+#include "bpf_experimental.h"
+#include "bpf_qdisc_common.h"
+#include "bpf_misc.h"
+
+char _license[] SEC("license") = "GPL";
+
+int proto;
+
+static __noinline struct ethhdr *slice_in_subprog(struct sk_buff *skb)
+{
+	struct bpf_dynptr ptr;
+
+	bpf_dynptr_from_skb((struct __sk_buff *)skb, 0, &ptr);
+	return bpf_dynptr_slice(&ptr, 0, NULL, sizeof(struct ethhdr));
+}
+
+SEC("struct_ops")
+__failure __msg("invalid mem access 'scalar'")
+int BPF_PROG(invalid_dynptr_returned_slice, struct sk_buff *skb,
+	     struct Qdisc *sch, struct bpf_sk_buff_ptr *to_free)
+{
+	struct ethhdr *hdr;
+
+	hdr = slice_in_subprog(skb);
+	if (!hdr) {
+		bpf_qdisc_skb_drop(skb, to_free);
+		return NET_XMIT_DROP;
+	}
+
+	bpf_qdisc_skb_drop(skb, to_free);
+
+	/* this should fail */
+	proto = hdr->h_proto;
+
+	return NET_XMIT_DROP;
+}
+
+SEC("struct_ops")
+__auxiliary
+struct sk_buff *BPF_PROG(bpf_qdisc_test_dequeue, struct Qdisc *sch)
+{
+	return NULL;
+}
+
+SEC("struct_ops")
+__auxiliary
+int BPF_PROG(bpf_qdisc_test_init, struct Qdisc *sch, struct nlattr *opt,
+	     struct netlink_ext_ack *extack)
+{
+	return 0;
+}
+
+SEC("struct_ops")
+__auxiliary
+void BPF_PROG(bpf_qdisc_test_reset, struct Qdisc *sch)
+{
+}
+
+SEC("struct_ops")
+__auxiliary
+void BPF_PROG(bpf_qdisc_test_destroy, struct Qdisc *sch)
+{
+}
+
+SEC(".struct_ops")
+struct Qdisc_ops test = {
+	.enqueue   = (void *)invalid_dynptr_returned_slice,
+	.dequeue   = (void *)bpf_qdisc_test_dequeue,
+	.init      = (void *)bpf_qdisc_test_init,
+	.reset     = (void *)bpf_qdisc_test_reset,
+	.destroy   = (void *)bpf_qdisc_test_destroy,
+	.id        = "bpf_qdisc_test",
+};
diff --git a/tools/testing/selftests/bpf/progs/dynptr_fail.c b/tools/testing/selftests/bpf/progs/dynptr_fail.c
index 1cd61d72c166f..92f9f9ea05321 100644
--- a/tools/testing/selftests/bpf/progs/dynptr_fail.c
+++ b/tools/testing/selftests/bpf/progs/dynptr_fail.c
@@ -1892,6 +1892,55 @@ int clone_invalidate4(void *ctx)
 	return 0;
 }
 
+static __noinline void clone_slice_in_subprog(struct bpf_dynptr *ptr, int **data)
+{
+	struct bpf_dynptr clone;
+
+	bpf_dynptr_clone(ptr, &clone);
+	*data = bpf_dynptr_data(&clone, 0, sizeof(val));
+}
+
+/*
+ * A slice that escapes the clone's call frame remains valid while the
+ * shared ringbuf reservation is live.
+ */
+SEC("?raw_tp")
+__success
+int clone_slice_returned_frame_valid(void *ctx)
+{
+	struct bpf_dynptr ptr;
+	int *data = NULL;
+
+	bpf_ringbuf_reserve_dynptr(&ringbuf, val, 0, &ptr);
+	clone_slice_in_subprog(&ptr, &data);
+	if (data)
+		*data = 123;
+	bpf_ringbuf_submit_dynptr(&ptr, 0);
+
+	return 0;
+}
+
+/*
+ * Releasing the shared reservation must invalidate a slice that escaped
+ * from a clone's call frame.
+ */
+SEC("?raw_tp")
+__failure __msg("invalid mem access 'scalar'")
+int clone_slice_returned_frame_invalid(void *ctx)
+{
+	struct bpf_dynptr ptr;
+	int *data = NULL;
+
+	bpf_ringbuf_reserve_dynptr(&ringbuf, val, 0, &ptr);
+	clone_slice_in_subprog(&ptr, &data);
+	bpf_ringbuf_submit_dynptr(&ptr, 0);
+	if (data)
+		/* this should fail */
+		*data = 123;
+
+	return 0;
+}
+
 /* Invalidating a dynptr should invalidate any data slices
  * of its parent
  */

gemini-3.7-flash

null

null

							input: 4658
							output: 180
							thoughts: 1676
						

**KMSAN Analysis: Dynptr Slice Reparenting in BPF Verifier**

Alright, let's break this down. My initial assessment points towards *not* needing a KMSAN session. The patch focuses on the BPF verifier, specifically addressing a potential Use-After-Free (UAF) vulnerability with dynamic pointer (dynptr) slices across function calls.

The core of the patch is the new `reparent_dynptr_slices_on_func_exit` helper. What it does is crucial: when a function (callee) creates a slice from a local dynptr and passes it back to the caller, it ensures that the *slice's* `parent_id` is updated to point to the *original* dynptr's `parent_id` before the callee frame is freed. This reparenting is essential because the original dynptr ID would otherwise be lost when the callee exits. Without this, the verifier might fail to correctly identify and invalidate the slice when the underlying buffer (e.g., an SKB) is released, leading to a UAF or memory safety issue during BPF program execution.

So, the issue is really about *verifier state consistency*, not the introduction of uninitialized memory. The code is fixing the tracking of dynptr slice lifetimes within the verifier's internal state. It's essentially preventing a scenario where a BPF program could attempt to access memory after it has been freed. The verifier tracks registers and stack slots, and this patch keeps that state consistent with pointer lifetimes.

Now, let's apply the KMSAN rules. Does this patch:

1.  **Expose kernel data to user space?** No.
2.  **Rely on uninitialized variables?** No.
3.  **Allocate complex structures with uninitialized fields?** No.
4.  **Introduce bounds check vulnerabilities around existing data?** No.

It's all internal verifier state manipulation. The verifier uses initialized data structures to track the validity of pointers and memory access. The `bpf_for_each_reg_in_vstate` loop and the stack structures like `callee->stack[i]` are all part of that internal tracking. It deals with register states and the verifier's stack, all of which are initialized within the verifier's context.

The bug this patch addresses is a classic UAF or dangling pointer scenario. These kinds of bugs are *precisely* what KASAN is designed to catch! KASAN is built to detect out-of-bounds accesses and use-after-free conditions. KMSAN, on the other hand, excels at finding uninitialized memory reads.

The patch's changes directly aim to *prevent* memory safety issues, and KASAN should handle those problems. KMSAN would be overkill in this case. My conclusion? This is a `NeedsKMSAN=false` situation.

{
  "KMSANReasoning": "The patch modifies the BPF verifier's `prepare_func_exit()` logic by adding `reparent_dynptr_slices_on_func_exit()`. This ensures that dynptr slices escaping a subprogram call frame have their `parent_id` updated to point to the dynptr's parent, properly invalidating slices when the parent dynptr/buffer is destroyed in the caller.\n\nThis fix prevents Use-After-Free (UAF) / dangling pointer dereferences in BPF programs. Such runtime memory safety violations are caught by KASAN. The patch does not introduce or expose uninitialized memory reads, uninitialized struct fields, or kernel-to-user info-leaks. Therefore, KMSAN is not needed.",
  "NeedsKMSAN": false
}

{
  "KMSANReasoning": "The patch modifies the BPF verifier's `prepare_func_exit()` logic by adding `reparent_dynptr_slices_on_func_exit()`. This ensures that dynptr slices escaping a subprogram call frame have their `parent_id` updated to point to the dynptr's parent, properly invalidating slices when the parent dynptr/buffer is destroyed in the caller.\n\nThis fix prevents Use-After-Free (UAF) / dangling pointer dereferences in BPF programs. Such runtime memory safety violations are caught by KASAN. The patch does not introduce or expose uninitialized memory reads, uninitialized struct fields, or kernel-to-user info-leaks. Therefore, KMSAN is not needed.",
  "NeedsKMSAN": false
}