digsig: add hash size comparision on signature verification

When pkcs_1_v1_5_decode_emsa() returns without error and hash sizes do
not match, hash comparision is not done and digsig_verify_rsa() returns
no error.  This is a bug and this patch fixes it.

The bug was introduced in v3.3 by commit b35e286a640f ("lib/digsig:
pkcs_1_v1_5_decode_emsa cleanup").

Cc: stable@vger.kernel.org
Signed-off-by: Dmitry Kasatkin <dmitry.kasatkin@intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 2 deletions

diff --git a/lib/digsig.c b/lib/digsig.c
index 286d558033e2..8c0e62975c88 100644
--- a/lib/digsig.c
+++ b/lib/digsig.c
@@ -163,9 +163,11 @@ static int digsig_verify_rsa(struct key *key,
         memcpy(out1 + head, p, l);
 
         err = pkcs_1_v1_5_decode_emsa(out1, len, mblen, out2, &len);
+        if (err)
+                goto err;
 
-        if (!err && len == hlen)
-                err = memcmp(out2, h, hlen);
+        if (len != hlen || memcmp(out2, h, hlen))
+                err = -EINVAL;
 
 err:
         mpi_free(in);