nvmet-tcp: Do not WARN on remotely-controlled oversized SGL allocations

commit 737a3b5 upstream.

When fuzzing the nvme target code, I tripped a kernel warning in
nvmet_tcp_map_data() because the length passed into the allocator is
controlled by the remote initiator.

A remote initiator that sends a command with an SGL claiming a huge
number, can create a scatterlist and iovec allocation of over 1 million
entries, which causes the backing kmalloc call to exceed MAX_PAGE_ORDER
and then the page allocator will trip on a WARN_ON_ONCE_GFP() message:

  WARNING: mm/page_alloc.c:5280 __alloc_frozen_pages_noprof
  Workqueue: nvmet_tcp_wq nvmet_tcp_io_work
  ...
  sgl_alloc_order
  nvmet_tcp_map_data
  nvmet_tcp_try_recv_pdu

As it's never good to trip a kernel warning remotely due to many systems
having panic-on-warn enabled, let's silence it by just add GFP_NOWARN to
the allocation flags.

Assisted-by: gkh_clanker_2000
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Keith Busch <kbusch@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: gregkh

drivers/nvme/target/tcp.c

@@ -401,14 +401,15 @@ static int nvmet_tcp_map_data(struct nvmet_tcp_cmd *cmd)
 	}
 	cmd->req.transfer_len += len;
 
-	cmd->req.sg = sgl_alloc(len, GFP_KERNEL, &cmd->req.sg_cnt);
+	cmd->req.sg = sgl_alloc(len, GFP_KERNEL | __GFP_NOWARN,
+				&cmd->req.sg_cnt);
 	if (!cmd->req.sg)
 		return NVME_SC_INTERNAL;
 	cmd->cur_sg = cmd->req.sg;
 
 	if (nvmet_tcp_has_data_in(cmd)) {
 		cmd->iov = kmalloc_array(cmd->req.sg_cnt,
-				sizeof(*cmd->iov), GFP_KERNEL);
+				sizeof(*cmd->iov), GFP_KERNEL | __GFP_NOWARN);
 		if (!cmd->iov)
 			goto err;
 	}