cifs: Fix use-after-free in SMB2_read

There is a KASAN use-after-free:
BUG: KASAN: use-after-free in SMB2_read+0x1136/0x1190
Read of size 8 at addr ffff8880b4e45e50 by task ln/1009

Should not release the 'req' because it will use in the trace.

Fixes: eccb4422cf97 ("smb3: Add ftrace tracepoints for improved SMB3 debugging")

Signed-off-by: ZhangXiaoxu <zhangxiaoxu5@huawei.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
CC: Stable <stable@vger.kernel.org> 4.18+
Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>
add_twarp_context(struct kvec *iov, unsigned int *num_iovec, __u64 timewarp)
{
	struct smb2_create_req *req = iov[0].iov_base;
	unsigned int num = *num_iovec;

	iov[num].iov_base = create_twarp_buf(timewarp);
	if (iov[num].iov_base == NULL)
		return -ENOMEM;
	iov[num].iov_len = sizeof(struct crt_twarp_ctxt);
	if (!req->CreateContextsOffset)
		req->CreateContextsOffset = cpu_to_le32(
				sizeof(struct smb2_create_req) +
				iov[num - 1].iov_len);
	le32_add_cpu(&req->CreateContextsLength, sizeof(struct crt_twarp_ctxt));
	*num_iovec = num + 1;
	return 0;
}

add_twarp_context(struct kvec *iov, unsigned int *num_iovec, __u64 timewarp)
{
	struct smb2_create_req *req = iov[0].iov_base;
	unsigned int num = *num_iovec;

	iov[num].iov_base = create_twarp_buf(timewarp);
	if (iov[num].iov_base == NULL)
		return -ENOMEM;
	iov[num].iov_len = sizeof(struct crt_twarp_ctxt);
	if (!req->CreateContextsOffset)
		req->CreateContextsOffset = cpu_to_le32(
				sizeof(struct smb2_create_req) +
				iov[num - 1].iov_len);
	le32_add_cpu(&req->CreateContextsLength, sizeof(struct crt_twarp_ctxt));
	*num_iovec = num + 1;
	return 0;
}
