net/smc: fix one NULL pointer dereference in smc_ib_is_sg_need_sync()

BUG: kernel NULL pointer dereference, address: 00000000000002ec
PGD 0 P4D 0
Oops: Oops: 0000 [#1] SMP PTI
CPU: 28 UID: 0 PID: 343 Comm: kworker/28:1 Kdump: loaded Tainted: G        OE       6.17.0-rc2+ #9 NONE
Tainted: [O]=OOT_MODULE, [E]=UNSIGNED_MODULE
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.15.0-1 04/01/2014
Workqueue: smc_hs_wq smc_listen_work [smc]
RIP: 0010:smc_ib_is_sg_need_sync+0x9e/0xd0 [smc]
...
Call Trace:
 <TASK>
 smcr_buf_map_link+0x211/0x2a0 [smc]
 __smc_buf_create+0x522/0x970 [smc]
 smc_buf_create+0x3a/0x110 [smc]
 smc_find_rdma_v2_device_serv+0x18f/0x240 [smc]
 ? smc_vlan_by_tcpsk+0x7e/0xe0 [smc]
 smc_listen_find_device+0x1dd/0x2b0 [smc]
 smc_listen_work+0x30f/0x580 [smc]
 process_one_work+0x18c/0x340
 worker_thread+0x242/0x360
 kthread+0xe7/0x220
 ret_from_fork+0x13a/0x160
 ret_from_fork_asm+0x1a/0x30
 </TASK>

If the software RoCE device is used, ibdev->dma_device is a null pointer.
As a result, the problem occurs. Null pointer detection is added to
prevent problems.

Fixes: 0ef69e7 ("net/smc: optimize for smc_sndbuf_sync_sg_for_device and smc_rmb_sync_sg_for_cpu")
Signed-off-by: Liu Jian <[email protected]>
Reviewed-by: Guangguan Wang <[email protected]>
Reviewed-by: Zhu Yanjun <[email protected]>
Reviewed-by: D. Wythe <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Paolo Abeni <[email protected]>

Author: liujian56

net/smc/smc_ib.c

@@ -742,6 +742,9 @@ bool smc_ib_is_sg_need_sync(struct smc_link *lnk,
 	unsigned int i;
 	bool ret = false;
 
+	if (!lnk->smcibdev->ibdev->dma_device)
+		return ret;
+
 	/* for now there is just one DMA address */
 	for_each_sg(buf_slot->sgt[lnk->link_idx].sgl, sg,
 		    buf_slot->sgt[lnk->link_idx].nents, i) {