From: Eduard Zingerman <eddyz87@gmail.com>
To: Dudu Lu <phx0fer@gmail.com>, bpf@vger.kernel.org
Cc: martin.lau@linux.dev, ast@kernel.org, daniel@iogearbox.net,
andrii@kernel.org
Subject: Re: [PATCH] bpf: btf: reject division by zero in btf_struct_walk for zero-size flex array elements
Date: Mon, 13 Apr 2026 14:43:25 -0700 [thread overview]
Message-ID: <5258cc4b95c2c835b699598f0ce24b3a318b5bc3.camel@gmail.com> (raw)
In-Reply-To: <20260413085033.71952-1-phx0fer@gmail.com>
On Mon, 2026-04-13 at 16:50 +0800, Dudu Lu wrote:
> btf_struct_walk() computes `off = (off - moff) % t->size` when handling
> access to a flexible array member. If the element type is a zero-size
> struct (e.g., `struct B {}`), t->size is 0 and this causes a division-
> by-zero exception. On x86 this triggers a #DE fault resulting in a
> kernel panic.
>
> The BTF validator does not reject zero-size structs: btf_struct_check_meta()
> passes trivially for vlen=0 structs, and btf_array_resolve() skips the
> overflow check for flex arrays (nelems=0). This allows a user to load
> crafted BTF containing `struct B {}; struct A { int x; struct B flex[]; }`
> and then trigger the crash when the verifier calls btf_struct_walk()
> during program load.
Could you please add a selftest as well?
[...]
prev parent reply other threads:[~2026-04-13 21:43 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-13 8:50 [PATCH] bpf: btf: reject division by zero in btf_struct_walk for zero-size flex array elements Dudu Lu
2026-04-13 9:26 ` bot+bpf-ci
2026-04-13 10:23 ` Leon Hwang
2026-04-13 10:31 ` Leon Hwang
2026-04-13 21:43 ` Eduard Zingerman [this message]
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