From: "Kumar Kartikeya Dwivedi" <memxor@gmail.com>
To: "Eric Biggers" <ebiggers@kernel.org>, <fsverity@lists.linux.dev>
Cc: <bpf@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
"Alexei Starovoitov" <ast@kernel.org>,
"Daniel Borkmann" <daniel@iogearbox.net>,
"Andrii Nakryiko" <andrii@kernel.org>,
"Eduard Zingerman" <eddyz87@gmail.com>,
"Martin KaFai Lau" <martin.lau@linux.dev>,
"Song Liu" <song@kernel.org>,
"Yonghong Song" <yonghong.song@linux.dev>,
"Emil Tsalapatis" <emil@etsalapatis.com>,
"Jiri Olsa" <jolsa@kernel.org>, <stable@vger.kernel.org>
Subject: Re: [PATCH] fsverity: Fix bpf_get_fsverity_digest() dynptr assumptions
Date: Sat, 01 Aug 2026 18:52:45 +0200 [thread overview]
Message-ID: <DKDRHTVNMQ2E.1FCTWQZO2EB7Z@gmail.com> (raw)
In-Reply-To: <20260731003925.2728977-1-ebiggers@kernel.org>
On Fri Jul 31, 2026 at 2:39 AM CEST, Eric Biggers wrote:
> The BPF verifier and the dynptr abstraction ensure that the memory space
> referenced by a dynptr remains valid. They do not, however, provide any
> guarantee that the contents of the memory are stable. kfuncs are
> expected to remain memory-safe even if concurrent modifications occur.
>
> bpf_get_fsverity_digest() didn't follow that: it could crash if
> arg->digest_size was concurrently modified.
>
> Fix that by using the known-good value hash_alg->digest_size instead.
>
This makes sense.
> Also correctly handle sizes over INT_MAX, which previously caused an
> integer overflow and crash. __bpf_dynptr_size() returns a u64.
>
I guess this occurs when using file dynptrs? Otherwise the size is capped to
DYNPTR_SIZE_MASK.
> Fixes: 67814c00de31 ("bpf, fsverity: Add kfunc bpf_get_fsverity_digest")
> Cc: stable@vger.kernel.org
> Signed-off-by: Eric Biggers <ebiggers@kernel.org>
> ---
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
> [...]
next prev parent reply other threads:[~2026-08-01 16:52 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-31 0:39 [PATCH] fsverity: Fix bpf_get_fsverity_digest() dynptr assumptions Eric Biggers
2026-08-01 16:52 ` Kumar Kartikeya Dwivedi [this message]
2026-08-01 17:15 ` Eric Biggers
2026-08-01 17:35 ` Kumar Kartikeya Dwivedi
2026-08-01 17:38 ` Kumar Kartikeya Dwivedi
2026-08-01 20:18 ` Eric Biggers
2026-08-01 20:47 ` Kumar Kartikeya Dwivedi
2026-08-01 21:02 ` Song Liu
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