From: Eduard Zingerman <eddyz87@gmail.com>
To: Kumar Kartikeya Dwivedi <memxor@gmail.com>, bpf@vger.kernel.org
Cc: Nicholas Carlini <npc@anthropic.com>,
Alexei Starovoitov <ast@kernel.org>,
Andrii Nakryiko <andrii@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Emil Tsalapatis <emil@etsalapatis.com>,
kkd@meta.com, kernel-team@meta.com
Subject: Re: [PATCH bpf v1 1/8] bpf: Check ancestor frames for rbtree callbacks
Date: Thu, 03 Sep 2026 15:40:55 -0700 [thread overview]
Message-ID: <ef8616d9adae2c2dc1371c407b86a504103e9cd1.camel@gmail.com> (raw)
In-Reply-To: <20260903214758.2727663-2-memxor@gmail.com>
On Thu, 2026-09-03 at 23:47 +0200, Kumar Kartikeya Dwivedi wrote:
> bpf_rbtree_add() invokes its comparator while the caller holds the root
> lock. The native insertion code retains raw parent and link pointers across
> the callback, so the verifier prohibits unlocking, consuming tree nodes,
> or changing RCU state from that callback.
>
> in_rbtree_lock_required_cb() only checks the innermost verifier frame.
> Static subprogram calls are permitted while holding a spin lock, and such a
> call pushes a frame without in_callback_fn set. Consequently, all callback
> restrictions disappear in the nested frame. The subprogram can unlock the
> tree, remove and drop the node being compared, then relock. Native insertion
> resumes with the stale parent pointer and links freed memory into the tree.
>
> Walk all active frames for the rbtree callback instead. Benign static
> subprograms remain permitted, while callback restrictions follow execution
> into nested frames.
>
> Fixes: a44b1334aadd ("bpf: Allow calling static subprogs while holding a bpf_spin_lock")
> Reported-by: Nicholas Carlini <npc@anthropic.com>
> Suggested-by: Nicholas Carlini <npc@anthropic.com>
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
> ---
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
...
next prev parent reply other threads:[~2026-09-03 22:40 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-03 21:47 [PATCH bpf v1 0/8] Misc bug fixes - part 2 Kumar Kartikeya Dwivedi
2026-09-03 21:47 ` [PATCH bpf v1 1/8] bpf: Check ancestor frames for rbtree callbacks Kumar Kartikeya Dwivedi
2026-09-03 22:40 ` Eduard Zingerman [this message]
2026-09-03 22:56 ` bot+bpf-ci
2026-09-03 21:47 ` [PATCH bpf v1 2/8] selftests/bpf: Check rbtree callback restrictions in subprogs Kumar Kartikeya Dwivedi
2026-09-03 22:56 ` bot+bpf-ci
2026-09-03 21:47 ` [PATCH bpf v1 3/8] bpf: Mark bpf_btf_find_by_name_kind() as sleepable Kumar Kartikeya Dwivedi
2026-09-03 22:15 ` Eduard Zingerman
2026-09-03 21:47 ` [PATCH bpf v1 4/8] selftests/bpf: Test btf lookup helper sleepability Kumar Kartikeya Dwivedi
2026-09-03 21:47 ` [PATCH bpf v1 5/8] bpf: Mark faultable stack helpers as sleepable Kumar Kartikeya Dwivedi
2026-09-03 22:00 ` Eduard Zingerman
2026-09-03 22:56 ` bot+bpf-ci
2026-09-03 21:47 ` [PATCH bpf v1 6/8] selftests/bpf: Check faultable stack helper contexts Kumar Kartikeya Dwivedi
2026-09-03 22:56 ` bot+bpf-ci
2026-09-03 21:47 ` [PATCH bpf v1 7/8] bpf: Reject legacy packet loads from callbacks Kumar Kartikeya Dwivedi
2026-09-03 21:58 ` Eduard Zingerman
2026-09-04 2:22 ` Alexei Starovoitov
2026-09-03 21:47 ` [PATCH bpf v1 8/8] selftests/bpf: " Kumar Kartikeya Dwivedi
2026-09-04 2:30 ` [PATCH bpf v1 0/8] Misc bug fixes - part 2 patchwork-bot+netdevbpf
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