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authorDavid Howells <dhowells@redhat.com>2012-09-21 23:28:05 +0100
committerRusty Russell <rusty@rustcorp.com.au>2012-10-08 13:50:17 +1030
commit0b1568a4536ff287a87908d7fc35c05bd7736a53 (patch)
tree2e2eab236c2fa23d568e0ee7179fbfdc5cf2b3ba /crypto
parent612e0fe99965a4028359cd1da5af56b7f6caf7f6 (diff)
RSA: Fix signature verification for shorter signatures
gpg can produce a signature file where length of signature is less than the modulus size because the amount of space an MPI takes up is kept as low as possible by discarding leading zeros. This regularly happens for several modules during the build. Fix it by relaxing check in RSA verification code. Thanks to Tomas Mraz and Miloslav Trmac for help. Signed-off-by: Milan Broz <mbroz@redhat.com> Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Diffstat (limited to 'crypto')
-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 9b31ee25a459..4a6a0696f8a3 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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