crypto: algif_skcipher - use ZERO_OR_NULL_PTR in skcipher_recvmsg_async

BugLink: https://bugs.launchpad.net/bugs/1868628

Nowdays, we trigger a oops:
...
kasan: GPF could be caused by NULL-ptr deref or user memory accessgeneral protection fault: 0000 [#1] SMP KASAN
...
Call Trace:
 [<ffffffff81a26fb1>] skcipher_recvmsg_async+0x3f1/0x1400 x86/../crypto/algif_skcipher.c:543
 [<ffffffff81a28053>] skcipher_recvmsg+0x93/0x7f0 x86/../crypto/algif_skcipher.c:723
 [<ffffffff823e43a4>] sock_recvmsg_nosec x86/../net/socket.c:702 [inline]
 [<ffffffff823e43a4>] sock_recvmsg x86/../net/socket.c:710 [inline]
 [<ffffffff823e43a4>] sock_recvmsg+0x94/0xc0 x86/../net/socket.c:705
 [<ffffffff823e464b>] sock_read_iter+0x27b/0x3a0 x86/../net/socket.c:787
 [<ffffffff817f479b>] aio_run_iocb+0x21b/0x7a0 x86/../fs/aio.c:1520
 [<ffffffff817f57c9>] io_submit_one x86/../fs/aio.c:1630 [inline]
 [<ffffffff817f57c9>] do_io_submit+0x6b9/0x10b0 x86/../fs/aio.c:1688
 [<ffffffff817f902d>] SYSC_io_submit x86/../fs/aio.c:1713 [inline]
 [<ffffffff817f902d>] SyS_io_submit+0x2d/0x40 x86/../fs/aio.c:1710
 [<ffffffff828b33c3>] tracesys_phase2+0x90/0x95

In skcipher_recvmsg_async, we use '!sreq->tsg' to determine does we
calloc fail. However, kcalloc may return ZERO_SIZE_PTR, and with this,
the latter sg_init_table will trigger the bug. Fix it be use ZERO_OF_NULL_PTR.

This function was introduced with ' commit a596999b ("crypto:
algif - change algif_skcipher to be asynchronous")', and has been removed
with 'commit e870456d ("crypto: algif_skcipher - overhaul memory
management")'.
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: yangerkun <yangerkun@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>
Signed-off-by: Kelsey Skunberg <kelsey.skunberg@canonical.com>

crypto/algif_skcipher.c

@@ -538,7 +538,7 @@ static int skcipher_recvmsg_async(struct socket *sock, struct msghdr *msg,
 	lock_sock(sk);
 	tx_nents = skcipher_all_sg_nents(ctx);
 	sreq->tsg = kcalloc(tx_nents, sizeof(*sg), GFP_KERNEL);
-	if (unlikely(!sreq->tsg))
+	if (unlikely(ZERO_OR_NULL_PTR(sreq->tsg)))
 		goto unlock;
 	sg_init_table(sreq->tsg, tx_nents);
 	memcpy(iv, ctx->iv, ivsize);