AI Trajectory

null

{
  "EnableConfigs": [
    "BPF_SYSCALL",
    "DEBUG_INFO_BTF"
  ],
  "FocusSymbols": [
    "check_kfunc_args",
    "__check_func_arg_reg_off"
  ],
  "Reasoning": "The patch modifies the BPF verifier to reject passing a modified pointer (with non-zero fixed offset) to a kfunc expecting a KF_ARG_PTR_TO_REFCOUNTED_KPTR. This is a functional change in the BPF verifier logic.",
  "WorthFuzzing": true
}

null

{
  "PatchDiff": "commit b1319cf8ea65db9a20a909018f9c88fac0d212e7\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate:   Tue Jun 23 06:36:44 2026 +0000\n\n    syz-cluster: applied patch under review\n\ndiff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c\nindex 2abc79dbf281c2..f65eff28ecd25e 100644\n--- a/kernel/bpf/verifier.c\n+++ b/kernel/bpf/verifier.c\n@@ -7990,9 +7990,10 @@ reg_find_field_offset(const struct bpf_reg_state *reg, s32 off, u32 fields)\n \treturn field;\n }\n \n-static int check_func_arg_reg_off(struct bpf_verifier_env *env,\n-\t\t\t\t  const struct bpf_reg_state *reg, argno_t argno,\n-\t\t\t\t  enum bpf_arg_type arg_type)\n+static int __check_func_arg_reg_off(struct bpf_verifier_env *env,\n+\t\t\t\t    const struct bpf_reg_state *reg, argno_t argno,\n+\t\t\t\t    enum bpf_arg_type arg_type,\n+\t\t\t\t    bool btf_id_fixed_off_ok)\n {\n \tu32 type = reg-\u003etype;\n \n@@ -8049,12 +8050,11 @@ static int check_func_arg_reg_off(struct bpf_verifier_env *env,\n \tcase PTR_TO_BTF_ID | MEM_ALLOC | NON_OWN_REF | MEM_RCU:\n \t\t/* When referenced PTR_TO_BTF_ID is passed to release function,\n \t\t * its fixed offset must be 0. In the other cases, fixed offset\n-\t\t * can be non-zero. This was already checked above. So pass\n-\t\t * fixed_off_ok as true to allow fixed offset for all other\n-\t\t * cases. var_off always must be 0 for PTR_TO_BTF_ID, hence we\n-\t\t * still need to do checks instead of returning.\n+\t\t * can be non-zero unless the caller requires otherwise.\n+\t\t * var_off always must be 0 for PTR_TO_BTF_ID, hence we still\n+\t\t * need to do checks instead of returning.\n \t\t */\n-\t\treturn __check_ptr_off_reg(env, reg, argno, true);\n+\t\treturn __check_ptr_off_reg(env, reg, argno, btf_id_fixed_off_ok);\n \tcase PTR_TO_CTX:\n \t\t/*\n \t\t * Allow fixed and variable offsets for syscall context, but\n@@ -8070,6 +8070,13 @@ static int check_func_arg_reg_off(struct bpf_verifier_env *env,\n \t}\n }\n \n+static int check_func_arg_reg_off(struct bpf_verifier_env *env,\n+\t\t\t\t  const struct bpf_reg_state *reg, argno_t argno,\n+\t\t\t\t  enum bpf_arg_type arg_type)\n+{\n+\treturn __check_func_arg_reg_off(env, reg, argno, arg_type, true);\n+}\n+\n static int check_arg_const_str(struct bpf_verifier_env *env,\n \t\t\t       struct bpf_reg_state *reg, argno_t argno)\n {\n@@ -11941,6 +11948,7 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_\n \t\tenum bpf_arg_type arg_type = ARG_DONTCARE;\n \t\targno_t argno = argno_from_arg(i + 1);\n \t\tint regno = reg_from_argno(argno);\n+\t\tbool btf_id_fixed_off_ok = true;\n \t\tu32 ref_id, type_size;\n \t\tbool is_ret_buf_sz = false;\n \t\tint kf_arg_type;\n@@ -12114,7 +12122,6 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_\n \t\tcase KF_ARG_PTR_TO_MEM:\n \t\tcase KF_ARG_PTR_TO_MEM_SIZE:\n \t\tcase KF_ARG_PTR_TO_CALLBACK:\n-\t\tcase KF_ARG_PTR_TO_REFCOUNTED_KPTR:\n \t\tcase KF_ARG_PTR_TO_CONST_STR:\n \t\tcase KF_ARG_PTR_TO_WORKQUEUE:\n \t\tcase KF_ARG_PTR_TO_TIMER:\n@@ -12128,6 +12135,10 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_\n \t\tcase KF_ARG_PTR_TO_CTX:\n \t\t\targ_type = ARG_PTR_TO_CTX;\n \t\t\tbreak;\n+\t\tcase KF_ARG_PTR_TO_REFCOUNTED_KPTR:\n+\t\t\targ_type = ARG_PTR_TO_BTF_ID;\n+\t\t\tbtf_id_fixed_off_ok = false;\n+\t\t\tbreak;\n \t\tdefault:\n \t\t\tverifier_bug(env, \"unknown kfunc arg type %d\", kf_arg_type);\n \t\t\treturn -EFAULT;\n@@ -12135,7 +12146,8 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_\n \n \t\tif (regno == meta-\u003erelease_regno)\n \t\t\targ_type |= OBJ_RELEASE;\n-\t\tret = check_func_arg_reg_off(env, reg, argno, arg_type);\n+\t\tret = __check_func_arg_reg_off(env, reg, argno, arg_type,\n+\t\t\t\t\t       btf_id_fixed_off_ok);\n \t\tif (ret \u003c 0)\n \t\t\treturn ret;\n \ndiff --git a/tools/testing/selftests/bpf/progs/refcounted_kptr_fail.c b/tools/testing/selftests/bpf/progs/refcounted_kptr_fail.c\nindex 7247a20c0a3bf5..024ef2aae20082 100644\n--- a/tools/testing/selftests/bpf/progs/refcounted_kptr_fail.c\n+++ b/tools/testing/selftests/bpf/progs/refcounted_kptr_fail.c\n@@ -13,12 +13,20 @@ struct node_acquire {\n \tstruct bpf_refcount refcount;\n };\n \n+struct node_refcounted {\n+\tlong key;\n+\tstruct bpf_list_node list;\n+\tstruct bpf_refcount refcount;\n+};\n+\n extern void bpf_rcu_read_lock(void) __ksym;\n extern void bpf_rcu_read_unlock(void) __ksym;\n \n #define private(name) SEC(\".data.\" #name) __hidden __attribute__((aligned(8)))\n private(A) struct bpf_spin_lock glock;\n private(A) struct bpf_rb_root groot __contains(node_acquire, node);\n+private(B) struct bpf_spin_lock lock;\n+private(B) struct bpf_list_head head __contains(node_refcounted, list);\n \n static bool less(struct bpf_rb_node *a, const struct bpf_rb_node *b)\n {\n@@ -93,6 +101,32 @@ long rbtree_refcounted_node_ref_escapes_owning_input(void *ctx)\n \treturn 0;\n }\n \n+SEC(\"?tc\")\n+__failure __msg(\"dereference of modified ptr_ ptr R1\")\n+long refcount_acquire_list_node_offset(void *ctx)\n+{\n+\tstruct node_refcounted *node, *base, *ref;\n+\tstruct bpf_list_node *list_node;\n+\n+\tnode = bpf_obj_new(typeof(*node));\n+\tif (!node)\n+\t\treturn 1;\n+\n+\tbpf_spin_lock(\u0026lock);\n+\tbpf_list_push_front(\u0026head, \u0026node-\u003elist);\n+\tlist_node = bpf_list_pop_front(\u0026head);\n+\tbpf_spin_unlock(\u0026lock);\n+\tif (!list_node)\n+\t\treturn 2;\n+\n+\tbase = container_of(list_node, struct node_refcounted, list);\n+\tref = bpf_refcount_acquire(list_node);\n+\tif (ref)\n+\t\tbpf_obj_drop(ref);\n+\tbpf_obj_drop(base);\n+\treturn 0;\n+}\n+\n SEC(\"?fentry.s/\" SYS_PREFIX \"sys_getpgid\")\n __failure __msg(\"function calls are not allowed while holding a lock\")\n int BPF_PROG(rbtree_fail_sleepable_lock_across_rcu,\n"
}

gemini-3.1-pro-preview

null

{
  "EnableConfigs": [
    "BPF_SYSCALL",
    "DEBUG_INFO_BTF"
  ],
  "FocusSymbols": [
    "check_kfunc_args",
    "__check_func_arg_reg_off"
  ],
  "Reasoning": "The patch modifies the BPF verifier to reject passing a modified pointer (with non-zero fixed offset) to a kfunc expecting a KF_ARG_PTR_TO_REFCOUNTED_KPTR. This is a functional change in the BPF verifier logic.",
  "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).

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.
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.
   Do not list too generic configs (we already have them enabled). Only list those that
   specifically cover the modified code. 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 b1319cf8ea65db9a20a909018f9c88fac0d212e7
Author: syz-cluster <triage@syzkaller.com>
Date:   Tue Jun 23 06:36:44 2026 +0000

    syz-cluster: applied patch under review

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 2abc79dbf281c2..f65eff28ecd25e 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -7990,9 +7990,10 @@ reg_find_field_offset(const struct bpf_reg_state *reg, s32 off, u32 fields)
 	return field;
 }
 
-static int check_func_arg_reg_off(struct bpf_verifier_env *env,
-				  const struct bpf_reg_state *reg, argno_t argno,
-				  enum bpf_arg_type arg_type)
+static int __check_func_arg_reg_off(struct bpf_verifier_env *env,
+				    const struct bpf_reg_state *reg, argno_t argno,
+				    enum bpf_arg_type arg_type,
+				    bool btf_id_fixed_off_ok)
 {
 	u32 type = reg->type;
 
@@ -8049,12 +8050,11 @@ static int check_func_arg_reg_off(struct bpf_verifier_env *env,
 	case PTR_TO_BTF_ID | MEM_ALLOC | NON_OWN_REF | MEM_RCU:
 		/* When referenced PTR_TO_BTF_ID is passed to release function,
 		 * its fixed offset must be 0. In the other cases, fixed offset
-		 * can be non-zero. This was already checked above. So pass
-		 * fixed_off_ok as true to allow fixed offset for all other
-		 * cases. var_off always must be 0 for PTR_TO_BTF_ID, hence we
-		 * still need to do checks instead of returning.
+		 * can be non-zero unless the caller requires otherwise.
+		 * var_off always must be 0 for PTR_TO_BTF_ID, hence we still
+		 * need to do checks instead of returning.
 		 */
-		return __check_ptr_off_reg(env, reg, argno, true);
+		return __check_ptr_off_reg(env, reg, argno, btf_id_fixed_off_ok);
 	case PTR_TO_CTX:
 		/*
 		 * Allow fixed and variable offsets for syscall context, but
@@ -8070,6 +8070,13 @@ static int check_func_arg_reg_off(struct bpf_verifier_env *env,
 	}
 }
 
+static int check_func_arg_reg_off(struct bpf_verifier_env *env,
+				  const struct bpf_reg_state *reg, argno_t argno,
+				  enum bpf_arg_type arg_type)
+{
+	return __check_func_arg_reg_off(env, reg, argno, arg_type, true);
+}
+
 static int check_arg_const_str(struct bpf_verifier_env *env,
 			       struct bpf_reg_state *reg, argno_t argno)
 {
@@ -11941,6 +11948,7 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
 		enum bpf_arg_type arg_type = ARG_DONTCARE;
 		argno_t argno = argno_from_arg(i + 1);
 		int regno = reg_from_argno(argno);
+		bool btf_id_fixed_off_ok = true;
 		u32 ref_id, type_size;
 		bool is_ret_buf_sz = false;
 		int kf_arg_type;
@@ -12114,7 +12122,6 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
 		case KF_ARG_PTR_TO_MEM:
 		case KF_ARG_PTR_TO_MEM_SIZE:
 		case KF_ARG_PTR_TO_CALLBACK:
-		case KF_ARG_PTR_TO_REFCOUNTED_KPTR:
 		case KF_ARG_PTR_TO_CONST_STR:
 		case KF_ARG_PTR_TO_WORKQUEUE:
 		case KF_ARG_PTR_TO_TIMER:
@@ -12128,6 +12135,10 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
 		case KF_ARG_PTR_TO_CTX:
 			arg_type = ARG_PTR_TO_CTX;
 			break;
+		case KF_ARG_PTR_TO_REFCOUNTED_KPTR:
+			arg_type = ARG_PTR_TO_BTF_ID;
+			btf_id_fixed_off_ok = false;
+			break;
 		default:
 			verifier_bug(env, "unknown kfunc arg type %d", kf_arg_type);
 			return -EFAULT;
@@ -12135,7 +12146,8 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
 
 		if (regno == meta->release_regno)
 			arg_type |= OBJ_RELEASE;
-		ret = check_func_arg_reg_off(env, reg, argno, arg_type);
+		ret = __check_func_arg_reg_off(env, reg, argno, arg_type,
+					       btf_id_fixed_off_ok);
 		if (ret < 0)
 			return ret;
 
diff --git a/tools/testing/selftests/bpf/progs/refcounted_kptr_fail.c b/tools/testing/selftests/bpf/progs/refcounted_kptr_fail.c
index 7247a20c0a3bf5..024ef2aae20082 100644
--- a/tools/testing/selftests/bpf/progs/refcounted_kptr_fail.c
+++ b/tools/testing/selftests/bpf/progs/refcounted_kptr_fail.c
@@ -13,12 +13,20 @@ struct node_acquire {
 	struct bpf_refcount refcount;
 };
 
+struct node_refcounted {
+	long key;
+	struct bpf_list_node list;
+	struct bpf_refcount refcount;
+};
+
 extern void bpf_rcu_read_lock(void) __ksym;
 extern void bpf_rcu_read_unlock(void) __ksym;
 
 #define private(name) SEC(".data." #name) __hidden __attribute__((aligned(8)))
 private(A) struct bpf_spin_lock glock;
 private(A) struct bpf_rb_root groot __contains(node_acquire, node);
+private(B) struct bpf_spin_lock lock;
+private(B) struct bpf_list_head head __contains(node_refcounted, list);
 
 static bool less(struct bpf_rb_node *a, const struct bpf_rb_node *b)
 {
@@ -93,6 +101,32 @@ long rbtree_refcounted_node_ref_escapes_owning_input(void *ctx)
 	return 0;
 }
 
+SEC("?tc")
+__failure __msg("dereference of modified ptr_ ptr R1")
+long refcount_acquire_list_node_offset(void *ctx)
+{
+	struct node_refcounted *node, *base, *ref;
+	struct bpf_list_node *list_node;
+
+	node = bpf_obj_new(typeof(*node));
+	if (!node)
+		return 1;
+
+	bpf_spin_lock(&lock);
+	bpf_list_push_front(&head, &node->list);
+	list_node = bpf_list_pop_front(&head);
+	bpf_spin_unlock(&lock);
+	if (!list_node)
+		return 2;
+
+	base = container_of(list_node, struct node_refcounted, list);
+	ref = bpf_refcount_acquire(list_node);
+	if (ref)
+		bpf_obj_drop(ref);
+	bpf_obj_drop(base);
+	return 0;
+}
+
 SEC("?fentry.s/" SYS_PREFIX "sys_getpgid")
 __failure __msg("function calls are not allowed while holding a lock")
 int BPF_PROG(rbtree_fail_sleepable_lock_across_rcu,

gemini-3.1-pro-preview

null

null

							input: 3843
							output: 20
							thoughts: 347
						

**Analyzing a BPF Verifier Patch**

Okay, so I'm looking at this patch that tweaks the BPF verifier, specifically within `kernel/bpf/verifier.c`. It's a pretty targeted change, but it has important implications for how we handle refcounted pointers with offsets in BPF kfuncs. The main thing is that `check_func_arg_reg_off` is now renamed to `__check_func_arg_reg_off` and takes an extra boolean, `btf_id_fixed_off_ok`. This change is coupled with an update to `check_kfunc_args` where we now pass `btf_id_fixed_off_ok = false` when dealing with `KF_ARG_PTR_TO_REFCOUNTED_KPTR`. The effect is that we are more restrictive now. We prevent passing a pointer with a fixed, non-zero offset to a kfunc when it is expecting a refcounted pointer. I see the intention is to prevent a scenario where a modified pointer gets misused.

The selftest `refcounted_kptr_fail.c` has a new test, `refcount_acquire_list_node_offset`, which aims to trigger this new verification. The test *expects* a failure, "dereference of modified ptr_ ptr R1", which confirms our suspicion about the change.

This is fundamentally a functional modification to the BPF verifier, which indicates a bug fix or, more likely, a newly added restriction. It’s definitely a change that could introduce subtle behavior differences, and therefore, it's a prime candidate for fuzzing. We need to be careful with this.

Now, let's identify the key focus symbols for further investigation. From the diff, it’s clear that the modified functions are: `__check_func_arg_reg_off`, `check_func_arg_reg_off` and `check_kfunc_args`. `check_kfunc_args` looks like a good place to start, given its central role in argument checking. `__check_func_arg_reg_off` is another critical area to examine.

We need to make sure we have the appropriate BPF configs enabled, specifically `CONFIG_BPF_SYSCALL`. Now, let's dive into the code and verify the impact of this change.

{
  "Expression": "check_kfunc_args"
}

{
  "Output": "kernel/bpf/verifier.c=11897=static bool check_css_task_iter_allowlist(struct bpf_verifier_env *env)\n--\nkernel/bpf/verifier.c-11912-\nkernel/bpf/verifier.c:11913:static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_arg_meta *meta,\nkernel/bpf/verifier.c-11914-\t\t\t    int insn_idx)\n--\nkernel/bpf/verifier.c=12898=static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,\n--\nkernel/bpf/verifier.c-12974-\t/* Check the arguments */\nkernel/bpf/verifier.c:12975:\terr = check_kfunc_args(env, \u0026meta, insn_idx);\nkernel/bpf/verifier.c-12976-\tif (err \u003c 0)\n--\nkernel/bpf/verifier.c-13261-\t\telse\nkernel/bpf/verifier.c:13262:\t\t\t/* scalar. ensured by check_kfunc_args() */\nkernel/bpf/verifier.c-13263-\t\t\tmark_btf_func_reg_size(env, regno, t-\u003esize);\n"
}

gemini-3.1-pro-preview

null

null

							input: 5071
							output: 21
							thoughts: 49
						

Okay, here's my interpretation of those thoughts, tailored for an expert audience, presented in the first person:

**Kernel Configuration Dependencies**

Alright, so I'm thinking about the kernel configurations required for this particular BPF program. It's clear that we'll definitely need `BPF_SYSCALL` – that's a given, since we're interacting with syscalls. But, because it relies on BTF IDs, I'm going to want to verify that `DEBUG_INFO_BTF` is also enabled. That's practically a prerequisite if we want symbol information and type information. I'm imagining it'd be quite difficult to work with without it.

Now, before I proceed too far down the implementation path, I should really check if there are any specific kernel configurations or build flags related to the `bpf_refcount_acquire` function itself. I should check if there's any specialized configuration that needs to be considered to use that particular function. I need to make sure I haven't missed anything obvious. I'll need to do some digging to make sure I haven't missed any specialized, or possibly even hidden, configuration options.

{
  "Expression": "bpf_refcount_acquire"
}

{
  "Output": "include/linux/bpf_verifier.h=1441=struct bpf_kfunc_call_arg_meta {\n--\ninclude/linux/bpf_verifier.h-1463-\t *     Record the local kptr type to be drop'd\ninclude/linux/bpf_verifier.h:1464:\t *   bpf_refcount_acquire (via KF_ARG_PTR_TO_REFCOUNTED_KPTR arg type)\ninclude/linux/bpf_verifier.h-1465-\t *     Record the local kptr type to be refcount_incr'd and use\n--\nkernel/bpf/helpers.c=2449=__bpf_kfunc void bpf_percpu_obj_drop_impl(void *p__alloc, void *meta__ign)\n--\nkernel/bpf/helpers.c-2454-/**\nkernel/bpf/helpers.c:2455: * bpf_refcount_acquire() - turn a local kptr into an owning reference\nkernel/bpf/helpers.c-2456- * @p__refcounted_kptr: non-owning local kptr\n--\nkernel/bpf/helpers.c-2463- */\nkernel/bpf/helpers.c:2464:__bpf_kfunc void *bpf_refcount_acquire(void *p__refcounted_kptr, struct btf_struct_meta *meta)\nkernel/bpf/helpers.c-2465-{\n--\nkernel/bpf/helpers.c-2480-\nkernel/bpf/helpers.c:2481:__bpf_kfunc void *bpf_refcount_acquire_impl(void *p__refcounted_kptr, void *meta__ign)\nkernel/bpf/helpers.c-2482-{\nkernel/bpf/helpers.c:2483:\treturn bpf_refcount_acquire(p__refcounted_kptr, meta__ign);\nkernel/bpf/helpers.c-2484-}\n--\nkernel/bpf/helpers.c=4813=BTF_ID_FLAGS(func, bpf_percpu_obj_drop_impl, KF_RELEASE)\nkernel/bpf/helpers.c:4814:BTF_ID_FLAGS(func, bpf_refcount_acquire, KF_ACQUIRE | KF_RET_NULL | KF_RCU | KF_IMPLICIT_ARGS)\nkernel/bpf/helpers.c:4815:BTF_ID_FLAGS(func, bpf_refcount_acquire_impl, KF_ACQUIRE | KF_RET_NULL | KF_RCU)\nkernel/bpf/helpers.c-4816-BTF_ID_FLAGS(func, bpf_list_push_front, KF_IMPLICIT_ARGS)\n--\nkernel/bpf/verifier.c=10989=enum special_kfunc_type {\n--\nkernel/bpf/verifier.c-10993-\tKF_bpf_obj_drop,\nkernel/bpf/verifier.c:10994:\tKF_bpf_refcount_acquire_impl,\nkernel/bpf/verifier.c:10995:\tKF_bpf_refcount_acquire,\nkernel/bpf/verifier.c-10996-\tKF_bpf_list_push_front_impl,\n--\nkernel/bpf/verifier.c=11066=BTF_ID(func, bpf_obj_drop)\nkernel/bpf/verifier.c:11067:BTF_ID(func, bpf_refcount_acquire_impl)\nkernel/bpf/verifier.c:11068:BTF_ID(func, bpf_refcount_acquire)\nkernel/bpf/verifier.c-11069-BTF_ID(func, bpf_list_push_front_impl)\n--\nkernel/bpf/verifier.c=11176=static bool is_bpf_percpu_obj_drop_kfunc(u32 func_id)\n--\nkernel/bpf/verifier.c-11181-\nkernel/bpf/verifier.c:11182:static bool is_bpf_refcount_acquire_kfunc(u32 func_id)\nkernel/bpf/verifier.c-11183-{\nkernel/bpf/verifier.c:11184:\treturn func_id == special_kfunc_list[KF_bpf_refcount_acquire] ||\nkernel/bpf/verifier.c:11185:\t       func_id == special_kfunc_list[KF_bpf_refcount_acquire_impl];\nkernel/bpf/verifier.c-11186-}\n--\nkernel/bpf/verifier.c=11209=static bool is_kfunc_ret_null(struct bpf_kfunc_call_arg_meta *meta)\nkernel/bpf/verifier.c-11210-{\nkernel/bpf/verifier.c:11211:\tif (is_bpf_refcount_acquire_kfunc(meta-\u003efunc_id) \u0026\u0026 meta-\u003earg_owning_ref)\nkernel/bpf/verifier.c-11212-\t\treturn false;\n--\nkernel/bpf/verifier.c=11617=static bool is_bpf_graph_api_kfunc(u32 btf_id)\n--\nkernel/bpf/verifier.c-11620-\t       is_bpf_rbtree_api_kfunc(btf_id) ||\nkernel/bpf/verifier.c:11621:\t       is_bpf_refcount_acquire_kfunc(btf_id);\nkernel/bpf/verifier.c-11622-}\n--\nkernel/bpf/verifier.c=12727=static int check_special_kfunc(struct bpf_verifier_env *env, struct bpf_kfunc_call_arg_meta *meta,\n--\nkernel/bpf/verifier.c-12815-\t\tinsn_aux-\u003ekptr_struct_meta = struct_meta;\nkernel/bpf/verifier.c:12816:\t} else if (is_bpf_refcount_acquire_kfunc(meta-\u003efunc_id)) {\nkernel/bpf/verifier.c-12817-\t\tmark_reg_known_zero(env, regs, BPF_REG_0);\n--\nkernel/bpf/verifier.c=12898=static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,\n--\nkernel/bpf/verifier.c-13118-\t\t     !is_bpf_percpu_obj_new_kfunc(meta.func_id) \u0026\u0026\nkernel/bpf/verifier.c:13119:\t\t     !is_bpf_refcount_acquire_kfunc(meta.func_id))) {\nkernel/bpf/verifier.c-13120-\t\t\tverbose(env, \"acquire kernel function does not return PTR_TO_BTF_ID\\n\");\n--\nkernel/bpf/verifier.c=19574=int bpf_fixup_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,\n--\nkernel/bpf/verifier.c-19622-\t\t   is_bpf_percpu_obj_drop_kfunc(desc-\u003efunc_id) ||\nkernel/bpf/verifier.c:19623:\t\t   is_bpf_refcount_acquire_kfunc(desc-\u003efunc_id)) {\nkernel/bpf/verifier.c-19624-\t\tstruct btf_struct_meta *kptr_struct_meta = env-\u003einsn_aux_data[insn_idx].kptr_struct_meta;\n--\nkernel/bpf/verifier.c-19632-\nkernel/bpf/verifier.c:19633:\t\tif (is_bpf_refcount_acquire_kfunc(desc-\u003efunc_id) \u0026\u0026 !kptr_struct_meta) {\nkernel/bpf/verifier.c-19634-\t\t\tverifier_bug(env, \"kptr_struct_meta expected at insn_idx %d\",\n--\ntools/sched_ext/include/scx/common.bpf.h=384=struct bpf_rb_node *bpf_rbtree_first(struct bpf_rb_root *root) __ksym;\ntools/sched_ext/include/scx/common.bpf.h-385-\ntools/sched_ext/include/scx/common.bpf.h:386:void *bpf_refcount_acquire_impl(void *kptr, void *meta) __ksym;\ntools/sched_ext/include/scx/common.bpf.h:387:#define bpf_refcount_acquire(kptr) bpf_refcount_acquire_impl(kptr, NULL)\ntools/sched_ext/include/scx/common.bpf.h-388-\n--\ntools/testing/selftests/bpf/progs/bpf_qdisc_fq.c=303=int BPF_PROG(bpf_fq_enqueue, struct sk_buff *skb, struct Qdisc *sch,\n--\ntools/testing/selftests/bpf/progs/bpf_qdisc_fq.c-344-\t\tif (fq_flow_is_detached(flow)) {\ntools/testing/selftests/bpf/progs/bpf_qdisc_fq.c:345:\t\t\tflow_copy = bpf_refcount_acquire(flow);\ntools/testing/selftests/bpf/progs/bpf_qdisc_fq.c-346-\n--\ntools/testing/selftests/bpf/progs/local_kptr_stash.c=234=long refcount_acquire_without_unstash(void *ctx)\n--\ntools/testing/selftests/bpf/progs/local_kptr_stash.c-249-\ntools/testing/selftests/bpf/progs/local_kptr_stash.c:250:\tp = bpf_refcount_acquire(s-\u003estashed);\ntools/testing/selftests/bpf/progs/local_kptr_stash.c-251-\tif (!p)\n--\ntools/testing/selftests/bpf/progs/rbtree_search.c=53=long rbtree_search(void *ctx)\n--\ntools/testing/selftests/bpf/progs/rbtree_search.c-64-\ntools/testing/selftests/bpf/progs/rbtree_search.c:65:\t\tm = bpf_refcount_acquire(n);\ntools/testing/selftests/bpf/progs/rbtree_search.c-66-\n--\ntools/testing/selftests/bpf/progs/rbtree_search.c-108-\ntools/testing/selftests/bpf/progs/rbtree_search.c:109:\tm = bpf_refcount_acquire(n);\ntools/testing/selftests/bpf/progs/rbtree_search.c-110-\tbpf_spin_unlock(\u0026glock0);\n--\ntools/testing/selftests/bpf/progs/rbtree_search.c=156=long test_##op##_spinlock_##dolock(void *ctx)\t\t\\\n--\ntools/testing/selftests/bpf/progs/rbtree_search.c-168-\tn = rb_entry(rb_n, struct node_data, r0);\t\\\ntools/testing/selftests/bpf/progs/rbtree_search.c:169:\tn = bpf_refcount_acquire(n);\t\t\t\\\ntools/testing/selftests/bpf/progs/rbtree_search.c-170-\tbpf_spin_unlock(\u0026glock0);\t\t\t\\\n--\ntools/testing/selftests/bpf/progs/rbtree_search_kptr.c=155=long rbtree_search_kptr_ref(void *ctx)\n--\ntools/testing/selftests/bpf/progs/rbtree_search_kptr.c-182-\t\t/* Unused reference */\ntools/testing/selftests/bpf/progs/rbtree_search_kptr.c:183:\t\ttnode_m = bpf_refcount_acquire(tnode_r);\ntools/testing/selftests/bpf/progs/rbtree_search_kptr.c-184-\t\tif (!tnode_m)\n--\ntools/testing/selftests/bpf/progs/refcounted_kptr.c=73=static long __insert_in_tree_and_list(struct bpf_list_head *head,\n--\ntools/testing/selftests/bpf/progs/refcounted_kptr.c-82-\ntools/testing/selftests/bpf/progs/refcounted_kptr.c:83:\tm = bpf_refcount_acquire(n);\ntools/testing/selftests/bpf/progs/refcounted_kptr.c-84-\tm-\u003ekey = 123;\n--\ntools/testing/selftests/bpf/progs/refcounted_kptr.c=106=static long __stash_map_insert_tree(int idx, int val, struct bpf_rb_root *root,\n--\ntools/testing/selftests/bpf/progs/refcounted_kptr.c-120-\tn-\u003ekey = val;\ntools/testing/selftests/bpf/progs/refcounted_kptr.c:121:\tm = bpf_refcount_acquire(n);\ntools/testing/selftests/bpf/progs/refcounted_kptr.c-122-\n--\ntools/testing/selftests/bpf/progs/refcounted_kptr.c=399=static struct node_data *__add_in_list(struct bpf_list_head *head,\n--\ntools/testing/selftests/bpf/progs/refcounted_kptr.c-407-\ntools/testing/selftests/bpf/progs/refcounted_kptr.c:408:\tnode_ref = bpf_refcount_acquire(node_new);\ntools/testing/selftests/bpf/progs/refcounted_kptr.c-409-\n--\ntools/testing/selftests/bpf/progs/refcounted_kptr.c=793=long rbtree_refcounted_node_ref_escapes(void *ctx)\n--\ntools/testing/selftests/bpf/progs/refcounted_kptr.c-802-\tbpf_rbtree_add(\u0026aroot, \u0026n-\u003enode, less_a);\ntools/testing/selftests/bpf/progs/refcounted_kptr.c:803:\tm = bpf_refcount_acquire(n);\ntools/testing/selftests/bpf/progs/refcounted_kptr.c-804-\tbpf_spin_unlock(\u0026alock);\n--\ntools/testing/selftests/bpf/progs/refcounted_kptr.c=815=long rbtree_refcounted_node_ref_escapes_owning_input(void *ctx)\n--\ntools/testing/selftests/bpf/progs/refcounted_kptr.c-822-\ntools/testing/selftests/bpf/progs/refcounted_kptr.c:823:\tm = bpf_refcount_acquire(n);\ntools/testing/selftests/bpf/progs/refcounted_kptr.c-824-\tm-\u003ekey = 2;\n--\ntools/testing/selftests/bpf/progs/refcounted_kptr.c=852=long rbtree_wrong_owner_remove_fail_a1(void *ctx)\n--\ntools/testing/selftests/bpf/progs/refcounted_kptr.c-858-\t\treturn 1;\ntools/testing/selftests/bpf/progs/refcounted_kptr.c:859:\tm = bpf_refcount_acquire(n);\ntools/testing/selftests/bpf/progs/refcounted_kptr.c-860-\n--\ntools/testing/selftests/bpf/progs/refcounted_kptr.c=1002=static int __insert_in_list(struct bpf_list_head *head, struct bpf_spin_lock *lock,\n--\ntools/testing/selftests/bpf/progs/refcounted_kptr.c-1010-\ntools/testing/selftests/bpf/progs/refcounted_kptr.c:1011:\tnode_ref = bpf_refcount_acquire(node_new);\ntools/testing/selftests/bpf/progs/refcounted_kptr.c-1012-\tnode_old = bpf_kptr_xchg(node, node_new);\n--\ntools/testing/selftests/bpf/progs/refcounted_kptr_fail.c=44=long rbtree_refcounted_node_ref_escapes(void *ctx)\n--\ntools/testing/selftests/bpf/progs/refcounted_kptr_fail.c-54-\t/* m becomes an owning ref but is never drop'd or added to a tree */\ntools/testing/selftests/bpf/progs/refcounted_kptr_fail.c:55:\tm = bpf_refcount_acquire(n);\ntools/testing/selftests/bpf/progs/refcounted_kptr_fail.c-56-\tbpf_spin_unlock(\u0026glock);\n--\ntools/testing/selftests/bpf/progs/refcounted_kptr_fail.c=66=long refcount_acquire_maybe_null(void *ctx)\n--\ntools/testing/selftests/bpf/progs/refcounted_kptr_fail.c-73-\t */\ntools/testing/selftests/bpf/progs/refcounted_kptr_fail.c:74:\tm = bpf_refcount_acquire(n);\ntools/testing/selftests/bpf/progs/refcounted_kptr_fail.c-75-\tif (m)\n--\ntools/testing/selftests/bpf/progs/refcounted_kptr_fail.c=85=long rbtree_refcounted_node_ref_escapes_owning_input(void *ctx)\n--\ntools/testing/selftests/bpf/progs/refcounted_kptr_fail.c-93-\t/* m becomes an owning ref but is never drop'd or added to a tree */\ntools/testing/selftests/bpf/progs/refcounted_kptr_fail.c:94:\tm = bpf_refcount_acquire(n);\ntools/testing/selftests/bpf/progs/refcounted_kptr_fail.c-95-\tm-\u003ekey = 2;\n--\ntools/testing/selftests/bpf/progs/refcounted_kptr_fail.c=106=long refcount_acquire_list_node_offset(void *ctx)\n--\ntools/testing/selftests/bpf/progs/refcounted_kptr_fail.c-122-\tbase = container_of(list_node, struct node_refcounted, list);\ntools/testing/selftests/bpf/progs/refcounted_kptr_fail.c:123:\tref = bpf_refcount_acquire(list_node);\ntools/testing/selftests/bpf/progs/refcounted_kptr_fail.c-124-\tif (ref)\n"
}

gemini-3.1-pro-preview

null

null

							input: 10357
							output: 125
							thoughts: 122
						

**My Assessment of the BPF Verifier Change**

Okay, so I'm looking at this patch. My immediate focus is on the configurations: `CONFIG_BPF_SYSCALL` and `CONFIG_DEBUG_INFO_BTF`. These are crucial context indicators – they tell me what parts of the BPF ecosystem this is touching. Given the nature of the change, I'm already inclined to mark it as `WorthFuzzing`. This is definitely something that needs thorough scrutiny.

The heart of the change revolves around the BPF verifier's handling of pointers passed to kfuncs, specifically those expecting `KF_ARG_PTR_TO_REFCOUNTED_KPTR`. The patch seems to be introducing a stricter check, rejecting modified pointers – meaning those with a non-zero fixed offset – in this particular scenario.

I need to dig deeper, but my initial thought is that this is a functional modification to the verifier logic. I'll be focusing my attention on `check_kfunc_args` and `__check_func_arg_reg_off` to grasp the nuances of this tightened check and its impact. This is something that could potentially expose subtle but important issues, so careful testing is in order.

{
  "EnableConfigs": [
    "BPF_SYSCALL",
    "DEBUG_INFO_BTF"
  ],
  "FocusSymbols": [
    "check_kfunc_args",
    "__check_func_arg_reg_off"
  ],
  "Reasoning": "The patch modifies the BPF verifier to reject passing a modified pointer (with non-zero fixed offset) to a kfunc expecting a KF_ARG_PTR_TO_REFCOUNTED_KPTR. This is a functional change in the BPF verifier logic.",
  "WorthFuzzing": true
}

{
  "EnableConfigs": [
    "BPF_SYSCALL",
    "DEBUG_INFO_BTF"
  ],
  "FocusSymbols": [
    "check_kfunc_args",
    "__check_func_arg_reg_off"
  ],
  "Reasoning": "The patch modifies the BPF verifier to reject passing a modified pointer (with non-zero fixed offset) to a kfunc expecting a KF_ARG_PTR_TO_REFCOUNTED_KPTR. This is a functional change in the BPF verifier logic.",
  "WorthFuzzing": true
}