nvme-tcp: check the data direction of a C2HData PDU

In the Linux kernel, the following vulnerability has been resolved:

nvme-tcp: check the data direction of a C2HData PDU

nvme_tcp_handle_c2h_data() finds the request by command id and checks
that it has a payload, but it does not check that the command asked for
data to be read. A controller that answers a write command with C2HData
therefore reaches nvme_tcp_recv_data(), where _copy_to_iter() hits
WARN_ON_ONCE(i->data_source) and returns 0. The receive path turns that
into -EFAULT and resets the controller.

No data is copied, so this is not memory corruption. What a controller
gets is a kernel warning it can raise at will, which is fatal on a host
booted with panic_on_warn.

The send path already knows the direction - it consults rq_data_dir()
when it builds a command - and nvme_tcp_handle_r2t() checks the length
and the offset of the request it names. The C2HData path does not check
the direction at all.

Reject a C2HData PDU whose command is not a read. Rejecting it fails
the command and resets the controller, as the neighbouring check in this
function does; what goes away is the warning.

[ 6.885580] ------------[ cut here ]------------
[ 6.886457] WARNING: lib/iov_iter.c:193 at _copy_to_iter+0x289/0x1330, CPU#0: kworker/0:1H/71
[ 6.888137] CPU: 0 UID: 0 PID: 71 Comm: kworker/0:1H Not tainted 7.2.0-rc5-NVMETCP-gf5098b6bae76 #1 PREEMPT(lazy)
[ 6.891165] Workqueue: nvme_tcp_wq nvme_tcp_io_work
[ 6.891875] RIP: 0010:_copy_to_iter+0x289/0x1330
[ 6.903739] Call Trace:
[ 6.904085] <TASK>
[ 6.909254] __skb_datagram_iter+0x433/0x820
[ 6.911026] skb_copy_datagram_iter+0x37/0x120
[ 6.911622] nvme_tcp_recv_skb+0xa07/0x4320
[ 6.913378] __tcp_read_sock+0x1ab/0x810
[ 6.915788] nvme_tcp_try_recv+0x152/0x1e0
[ 6.918222] nvme_tcp_io_work+0x1e4/0x6c0
[ 6.926906] </TASK>
[ 6.927226] ---[ end trace 0000000000000000 ]---
[ 6.927878] nvme nvme0: queue 1 failed to copy request 0x71 data
[ 6.928709] nvme nvme0: receive failed: -14