On Thu 2013-08-22 19:01:46, Lee, Chun-Yi wrote:
> 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 <jkos...@suse.cz>
> Signed-off-by: Lee, Chun-Yi <j...@suse.com>
> - 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);
Spot a crash waiting to happen.
Pavel
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