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-rw-r--r--crypto/asymmetric_keys/rsa.c14
1 files changed, 11 insertions, 3 deletions
diff --git a/crypto/asymmetric_keys/rsa.c b/crypto/asymmetric_keys/rsa.c
index 9b31ee2..4a6a069 100644
--- a/crypto/asymmetric_keys/rsa.c
+++ b/crypto/asymmetric_keys/rsa.c
@@ -224,15 +224,23 @@ static int RSA_verify_signature(const struct public_key *key,
return -ENOTSUPP;
/* (1) Check the signature size against the public key modulus size */
- k = (mpi_get_nbits(key->rsa.n) + 7) / 8;
+ k = mpi_get_nbits(key->rsa.n);
+ tsize = mpi_get_nbits(sig->rsa.s);
- tsize = (mpi_get_nbits(sig->rsa.s) + 7) / 8;
+ /* According to RFC 4880 sec 3.2, length of MPI is computed starting
+ * from most significant bit. So the RFC 3447 sec 8.2.2 size check
+ * must be relaxed to conform with shorter signatures - so we fail here
+ * only if signature length is longer than modulus size.
+ */
pr_devel("step 1: k=%zu size(S)=%zu\n", k, tsize);
- if (tsize != k) {
+ if (k < tsize) {
ret = -EBADMSG;
goto error;
}
+ /* Round up and convert to octets */
+ k = (k + 7) / 8;
+
/* (2b) Apply the RSAVP1 verification primitive to the public key */
ret = RSAVP1(key, sig->rsa.s, &m);
if (ret < 0)
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