[PATCH] nvme-tcp: reject C2HData for a non-read command

A malicious or buggy controller can send C2HData PDUs in response to a
WRITE command.  nvme_tcp_handle_c2h_data() accepts them as long as the
request has payload bytes and a current bio, which is true for writes,
so the receive path ends up copying the incoming data into the
request's iterator.  That iterator was initialized from rq_data_dir(rq)
in nvme_tcp_init_iter(), i.e. ITER_SOURCE for a write, and
_copy_to_iter() refuses to copy into a source iterator: it triggers its
WARN_ON_ONCE() and returns 0, the short copy fails with -EFAULT, and
the connection is torn down into error recovery.  The write never
completes: every reconnect reissues it and a malicious target answers
with C2HData again, keeping the controller in a permanent
reset/reconnect loop.  With panic_on_warn this is an outright crash.

C2HData carries data transferred from the controller to the host and
is only valid for commands that read data from the device; write data
travels host to controller in H2CData PDUs solicited by R2T.  This was
reproduced against a target modified to reply to a WRITE with C2HData:
the host logs

    WARNING: CPU: 0 PID: ... at lib/iov_iter.c _copy_to_iter
    Workqueue: nvme_tcp_wq nvme_tcp_io_work [nvme_tcp]

and the controller cycles through reset/reconnect without the write
ever completing.

Reject C2HData for any non-read command.  This is the symmetric case
of commit 6efbc52237fa ("nvme-tcp: fix host memory disclosure on R2T
for a read command"), which added the mirror-image direction check to
nvme_tcp_handle_r2t().

Fixes: 3f2304f8c6d6 ("nvme-tcp: add NVMe over TCP host driver")
Cc: [email protected]
Reported-by: Abaci <[email protected]>
Assisted-by: abaci:qwen3.8-max
Signed-off-by: Chuyf26 <[email protected]>
---
 drivers/nvme/host/tcp.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/nvme/host/tcp.c b/drivers/nvme/host/tcp.c
--- a/drivers/nvme/host/tcp.c
+++ b/drivers/nvme/host/tcp.c
@@ -685,6 +685,13 @@
 	}
 
 	req = blk_mq_rq_to_pdu(rq);
+	if (unlikely(rq_data_dir(rq) != READ)) {
+		dev_err(queue->ctrl->ctrl.device,
+			"req %d unexpected c2hdata for a non-read command\n",
+			rq->tag);
+		return -EPROTO;
+	}
+
 	if (!blk_rq_payload_bytes(rq) || !req->curr_bio || !req->data_len) {
 		dev_err(queue->ctrl->ctrl.device,
 			"queue %d tag %#x unexpected data\n",
-- 
2.43.5