From: Ihor Solodrai <ihor.solodrai@linux.dev>
To: Alexei Starovoitov <ast@kernel.org>,
Andrii Nakryiko <andrii@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Eduard Zingerman <eddyz87@gmail.com>,
Kumar Kartikeya Dwivedi <memxor@gmail.com>
Cc: Amery Hung <ameryhung@gmail.com>,
Emil Tsalapatis <emil@etsalapatis.com>,
Nicholas Carlini <npc@anthropic.com>,
bpf@vger.kernel.org, linux-kernel@vger.kernel.org,
kernel-team@meta.com
Subject: [PATCH bpf-next v2 08/11] bpf: Scope the bpf_user_ringbuf_drain() dynptr to its callback frame
Date: Fri, 9 Oct 2026 13:27:55 -0700 [thread overview]
Message-ID: <20261009202759.50520-9-ihor.solodrai@linux.dev> (raw)
In-Reply-To: <20261009202759.50520-1-ihor.solodrai@linux.dev>
The dynptr argument to a bpf_user_ringbuf_drain() callback points to a
descriptor on the helper's stack. The descriptor and the sample it
describes are valid only during that callback invocation.
The callback can save the dynptr pointer, a slice, or a clone in the
caller's frame and use it after the drain returns. An escaped descriptor
pointer can allow arbitrary kernel read/write once the helper's stack
is reused.
The verifier assigns the dynptr a type and an id, but does not tie it
or its descendants to the callback's lifetime.
Anchor R1 to a frame reference so the argument and its descendants are
invalidated when the callback frame is popped.
Reported-by: Nicholas Carlini <npc@anthropic.com>
Signed-off-by: Ihor Solodrai <ihor.solodrai@linux.dev>
---
kernel/bpf/verifier.c | 15 ++++++++++-----
1 file changed, 10 insertions(+), 5 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index c969fef2d452..edc78e50dc22 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -713,11 +713,12 @@ static void mark_dynptr_stack_regs(struct bpf_verifier_env *env,
__mark_dynptr_reg(sreg2, type, false, id, parent_id);
}
-static void mark_dynptr_cb_reg(struct bpf_verifier_env *env,
- struct bpf_reg_state *reg,
- enum bpf_dynptr_type type)
+static int mark_dynptr_cb_reg(struct bpf_verifier_env *env, struct bpf_verifier_state *state,
+ struct bpf_func_state *callee, u32 regno,
+ enum bpf_dynptr_type type)
{
- __mark_dynptr_reg(reg, type, true, ++env->id_gen, 0);
+ __mark_dynptr_reg(&callee->regs[regno], type, true, 0, 0);
+ return mark_frame_scoped_arg(env, state, callee, regno);
}
static int destroy_if_dynptr_stack_slot(struct bpf_verifier_env *env,
@@ -11456,11 +11457,15 @@ static int set_user_ringbuf_callback_state(struct bpf_verifier_env *env,
struct bpf_func_state *callee,
int insn_idx)
{
+ int err;
+
/* bpf_user_ringbuf_drain(struct bpf_map *map, void *callback_fn, void
* callback_ctx, u64 flags);
* callback_fn(const struct bpf_dynptr_t* dynptr, void *callback_ctx);
*/
- mark_dynptr_cb_reg(env, &callee->regs[BPF_REG_1], BPF_DYNPTR_TYPE_LOCAL);
+ err = mark_dynptr_cb_reg(env, state, callee, BPF_REG_1, BPF_DYNPTR_TYPE_LOCAL);
+ if (err)
+ return err;
callee->regs[BPF_REG_2] = caller->regs[BPF_REG_3];
callee->in_callback_fn = true;
--
2.56.0
next prev parent reply other threads:[~2026-10-09 20:28 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-09 20:27 [PATCH bpf-next v2 00/11] bpf: Scope callback arguments to their frame Ihor Solodrai
2026-10-09 20:27 ` [PATCH bpf-next v2 01/11] bpf: Set up callee state outside of setup_func_entry() Ihor Solodrai
2026-10-09 20:27 ` [PATCH bpf-next v2 02/11] bpf: Pass the owning verifier state to callback setters Ihor Solodrai
2026-10-09 20:27 ` [PATCH bpf-next v2 03/11] bpf: Append complete reference states Ihor Solodrai
2026-10-09 20:27 ` [PATCH bpf-next v2 04/11] bpf: Separate reference removal from descendant invalidation Ihor Solodrai
2026-10-09 20:27 ` [PATCH bpf-next v2 05/11] bpf: Share map-backed callback register setup Ihor Solodrai
2026-10-09 20:27 ` [PATCH bpf-next v2 06/11] bpf: Rely on callback frame initialization defaults Ihor Solodrai
2026-10-09 20:27 ` [PATCH bpf-next v2 07/11] bpf: Introduce REF_TYPE_FRAME in the verifier Ihor Solodrai
2026-10-09 20:48 ` sashiko-bot
2026-10-10 3:26 ` Ihor Solodrai
2026-10-09 20:27 ` Ihor Solodrai [this message]
2026-10-09 20:27 ` [PATCH bpf-next v2 09/11] selftests/bpf: Cover the user ringbuf callback dynptr lifetime Ihor Solodrai
2026-10-09 20:27 ` [PATCH bpf-next v2 10/11] bpf: Scope the bpf_for_each_map_elem() array key to the callback frame Ihor Solodrai
2026-10-09 20:27 ` [PATCH bpf-next v2 11/11] selftests/bpf: Cover callback-frame map key lifetime Ihor Solodrai
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