Re: [PATCH] fsverity: Fix bpf_get_fsverity_digest() dynptr assumptions
"Kumar Kartikeya Dwivedi" <[email protected]>
| Newsgroups | org.kernel.vger.stable,dev.linux.lists.fsverity,org.kernel.vger.bpf,org.kernel.vger.linux-kernel |
|---|---|
| Message-ID | <[email protected]> |
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: [email protected]
> Signed-off-by: Eric Biggers <[email protected]>
> ---
Acked-by: Kumar Kartikeya Dwivedi <[email protected]>
> [...]