Subject: Re: [PATCH net v2] net/smc: fix one NULL pointer dereference in smc_ib_is_sg_need_sync()

From: "yanjun.zhu" <[email-masked]>
Date: Thu, 28 Aug 2025 11:24:43 -0700

On 8/28/25 5:41 AM, Liu Jian wrote:
> 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.

Normally, SoftRoCE relies on the DMA capabilities of the underlying NIC 
device. In SMC, if DMA will play an important role in the subsequent 
operations, we can leverage the NIC device’s DMA.

If DMA is not required for the upcoming actions, then this kind of 
checking is sufficient.

Reviewed-by: Zhu Yanjun <[email-masked]>

Zhu Yanjun

> 
> Fixes: 0ef69e788411c ("net/smc: optimize for smc_sndbuf_sync_sg_for_device and smc_rmb_sync_sg_for_cpu")
> Signed-off-by: Liu Jian <[email-masked]>
> ---
> v1->v2:
> move the check outside of loop.
>   net/smc/smc_ib.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/net/smc/smc_ib.c b/net/smc/smc_ib.c
> index 53828833a3f7..a42ef3f77b96 100644
> --- a/net/smc/smc_ib.c
> +++ b/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) {