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: stable@vger.kernel.org Signed-off-by: Eric Biggers --- 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