[PATCH bpf v2 2/2] fsverity: Fix silent truncation in bpf_get_fsverity_digest()
Eric Biggers <[email protected]>
| Newsgroups | gmane.linux.kernel.stable,gmane.linux.kernel.bpf,gmane.linux.kernel |
|---|---|
| Message-ID | <[email protected]> |
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: 67814c00de31 ("bpf, fsverity: Add kfunc bpf_get_fsverity_digest")
Cc: [email protected]
Signed-off-by: Eric Biggers <[email protected]>
---
fs/verity/measure.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/fs/verity/measure.c b/fs/verity/measure.c
index f8b3526af004..68dfccb69772 100644
--- a/fs/verity/measure.c
+++ b/fs/verity/measure.c
@@ -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)
--
2.55.0