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

From: Leon Romanovsky <[email-masked]>
Date: Tue, 9 Sep 2025 12:45:32 +0300

On Thu, Aug 28, 2025 at 08:41:17PM +0800, 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.
> 
> 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;

Please use ib_uses_virt_dma() function for that.

It is clearly stated in the code:
  2784 struct ib_device {
  2785         /* Do not access @dma_device directly from ULP nor from HW drivers. */
  2786         struct device                *dma_device;     

Thanks

> +
>  	/* 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) {
> -- 
> 2.34.1
> 
>