From: Eduard Zingerman <eddyz87@gmail.com>
To: Kumar Kartikeya Dwivedi <memxor@gmail.com>, bpf@vger.kernel.org
Cc: syzbot+7b47f87674e9a1569110@syzkaller.appspotmail.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 1/2] bpf: Reject non-scalar bpf_loop iteration counts
Date: Sat, 05 Sep 2026 20:46:30 -0700 [thread overview]
Message-ID: <ae51c26ca2a9a66c00a037d332ca0fa4da333a8e.camel@gmail.com> (raw)
In-Reply-To: <20260905014735.1452988-2-memxor@gmail.com>
On Sat, 2026-09-05 at 03:47 +0200, Kumar Kartikeya Dwivedi wrote:
> bpf_loop() declares its nr_loops argument as ARG_ANYTHING. Privileged
> programs may pass pointer values to such arguments, so check_func_arg()
> lets a pointer-valued R1 reach the helper-specific checks.
>
> Since commit bb124da69c47 ("bpf: keep track of max number of bpf_loop
> callback iterations"), the verifier marks R1 precise and reads its upper
> bound to limit callback simulation. Precision backtracking only accepts
> scalar registers, so passing a pointer instead triggers the "backtracking
> misuse" verifier warning. Kernels with panic_on_warn enabled subsequently
> panic.
>
> Introduce ARG_SCALAR for helper arguments that only accept scalar values
> and use it for bpf_loop() nr_loops. Generic helper argument validation then
> rejects pointers before loop inlining and precision processing.
>
> Fixes: bb124da69c47 ("bpf: keep track of max number of bpf_loop callback iterations")
> Reported-by: syzbot+7b47f87674e9a1569110@syzkaller.appspotmail.com
> Closes: https://lore.kernel.org/bpf/6a9ad24c.b5d4176b.238c3e.0001.GAE@google.com/
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
> ---
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Looks like there are no other instances of this bug.
next prev parent reply other threads:[~2026-09-06 3:46 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-05 1:47 [PATCH bpf v1 0/2] Fix bpf_loop syzbot report Kumar Kartikeya Dwivedi
2026-09-05 1:47 ` [PATCH bpf v1 1/2] bpf: Reject non-scalar bpf_loop iteration counts Kumar Kartikeya Dwivedi
2026-09-05 1:57 ` sashiko-bot
2026-09-05 5:56 ` Kumar Kartikeya Dwivedi
2026-09-06 3:46 ` Eduard Zingerman [this message]
2026-09-05 1:47 ` [PATCH bpf v1 2/2] selftests/bpf: Test pointer bpf_loop iteration count rejection Kumar Kartikeya Dwivedi
2026-09-06 3:45 ` Eduard Zingerman
2026-09-06 4:10 ` [PATCH bpf v1 0/2] Fix bpf_loop syzbot report patchwork-bot+netdevbpf
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