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fsverity: Fix silent truncation in bpf_get_fsverity_digest()

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bpf_get_fsverity_digest() silently truncates the digest if the provided
buffer is too small.  This is a footgun, and it doesn't match the
semantics of the equivalent UAPI (FS_IOC_MEASURE_VERITY).

Change it to return -EOVERFLOW instead, matching FS_IOC_MEASURE_VERITY.

Fixes: 67814c00de ("bpf, fsverity: Add kfunc bpf_get_fsverity_digest")
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
Acked-by: Song Liu <song@kernel.org>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/bpf/20260803181232.14743-3-ebiggers@kernel.org
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
This commit is contained in:
Eric Biggers
2026-08-04 09:24:23 +02:00
committed by Kumar Kartikeya Dwivedi
parent 3e8ec7c038
commit 7c68ed5c5a
1 changed files with 5 additions and 4 deletions
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fs/verity/measure.c
+5 -4
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@@ -144,14 +144,15 @@ __bpf_kfunc int bpf_get_fsverity_digest(struct file *file, const struct bpf_dynp
hash_alg = vi->tree_params.hash_alg;
out_digest_sz = dynptr_sz - sizeof(struct fsverity_digest);
if (out_digest_sz < hash_alg->digest_size)
return -EOVERFLOW;
arg->digest_algorithm = hash_alg - fsverity_hash_algs;
arg->digest_size = hash_alg->digest_size;
out_digest_sz = dynptr_sz - sizeof(struct fsverity_digest);
/* copy digest */
memcpy(arg->digest, vi->file_digest,
min(hash_alg->digest_size, out_digest_sz));
memcpy(arg->digest, vi->file_digest, hash_alg->digest_size);
/* fill the extra buffer with zeros */
if (out_digest_sz > hash_alg->digest_size)