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    SubjectRe: [PATCH 07/18] asymmetric keys: explicitly add the leading zero byte to encoded message
    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 <jkosina@suse.cz>
    > Signed-off-by: Lee, Chun-Yi <jlee@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
    --
    (english) http://www.livejournal.com/~pavelmachek
    (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html


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