Per PKCS1 spec, the EMSA-PKCS1-v1_5 encoded message is leading by 0x00 0x01 in
its first 2 bytes. The leading zero byte is suppressed by MPI so we pass a
pointer to the _preceding_ byte to RSA_verify() in original code, but it has
risk for the byte is not zero because it's not in EM buffer's scope, neither
RSA_verify() nor mpi_get_buffer() didn't take care the leading byte.
To avoid the risk, that's better we explicitly add the leading zero byte to EM
for pass to RSA_verify(). This patch allocate a _EM buffer to capture the
result from RSA_I2OSP(), then set the first byte to zero in EM and copy the
remaining bytes from _EM.
Reviewed-by: Jiri Kosina
Signed-off-by: Lee, Chun-Yi
---
crypto/asymmetric_keys/rsa.c | 14 ++++++++++----
1 files changed, 10 insertions(+), 4 deletions(-)
diff --git a/crypto/asymmetric_keys/rsa.c b/crypto/asymmetric_keys/rsa.c
index e60defe..1fadc7f 100644
--- a/crypto/asymmetric_keys/rsa.c
+++ b/crypto/asymmetric_keys/rsa.c
@@ -401,6 +401,7 @@ static int RSA_verify_signature(const struct public_key *key,
/* Variables as per RFC3447 sec 8.2.2 */
const u8 *H = sig->digest;
u8 *EM = NULL;
+ u8 *_EM = NULL;
MPI m = NULL;
size_t k;
@@ -435,14 +436,19 @@ static int RSA_verify_signature(const struct public_key *key,
/* (2c) Convert the message representative (m) to an encoded message
* (EM) of length k octets.
*
- * NOTE! The leading zero byte is suppressed by MPI, so we pass a
- * pointer to the _preceding_ byte to RSA_verify()!
+ * NOTE! The leading zero byte is suppressed by MPI, so we add it
+ * back to EM before input to RSA_verify()!
*/
- ret = RSA_I2OSP(m, k, &EM);
+ ret = RSA_I2OSP(m, k, &_EM);
if (ret < 0)
goto error;
- ret = RSA_verify(H, EM - 1, k, sig->digest_size,
+ EM = kmalloc(k, GFP_KERNEL);
+ memset(EM, 0, 1);
+ memcpy(EM + 1, _EM, k-1);
+ kfree(_EM);
+
+ ret = RSA_verify(H, EM, k, sig->digest_size,
RSA_ASN1_templates[sig->pkey_hash_algo].data,
RSA_ASN1_templates[sig->pkey_hash_algo].size);
--
1.6.4.2
--
To unsubscribe, e-mail: opensuse-kernel+unsubscribe@opensuse.org
To contact the owner, e-mail: opensuse-kernel+owner@opensuse.org
