From mboxrd@z Thu Jan  1 00:00:00 1970
From: Yao Dongdong <yaodongdong@huawei.com>
Subject: [Question] AEAD crypto api for userspace can't deal with a PTlen=0
 vector
Date: Thu, 7 May 2015 17:44:53 +0800
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Cc: <linux-crypto@vger.kernel.org>, "Lihui (Eric)" <lihui8@huawei.com>
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while we use crypto api for userspace to do vectors test for AEAD(aes-gcm),
we encounter a problem. There are some test vector's PTlen is 0,for example:
[Keylen = 128]
[IVlen = 96]
[PTlen = 0]
[AADlen = 0]
[Taglen = 128]

Count = 0
Key = 7e93936b2e2188cfa9c9882ad901312f
IV = b6879804163b9eaf5bfe5218
CT =
AAD =
Tag = aa77daf382d0d63480ff8c8a2dee149e

In testing vectors like that, we will get an error result that the decrypt
return is success but the right return is a ghash verify fail.
After digging into the kernel(3.10) code, we find the function sock_aio_read
in net/socket.c has a judgement of iocb->ki_left which will be 0 when we
do an aes-gcm decrypt decribed above.

static ssize_t sock_aio_read(struct kiocb *iocb, const struct iovec *iov,
                unsigned long nr_segs, loff_t pos)
{
    struct sock_iocb siocb, *x;

    if (pos != 0)
        return -ESPIPE;

    if (iocb->ki_left == 0) /* Match SYS5 behaviour */
        return 0;

    x = alloc_sock_iocb(iocb, &siocb);
    if (!x)
        return -ENOMEM;
    return do_sock_read(&x->async_msg, iocb, iocb->ki_filp, iov, nr_segs);
}

So it directly return before calling aes-gcm decrypt.

How can we deal with that?

-- 
Kind regards,
Yao Dongdong