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 <jkosina@xxxxxxx> Signed-off-by: Lee, Chun-Yi <jlee@xxxxxxxx> --- 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 from this list: send the line "unsubscribe linux-crypto" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
