Subject: Re: [PATCH net] net/smc: Avoid to access invalid RMBs' MRs in SMCRv1 ADD LINK CONT

From: Tony Lu <[email-masked]>
Date: Fri, 2 Jun 2023 15:42:34 +0800

On Thu, Jun 01, 2023 at 04:41:52PM +0800, Wen Gu wrote:
> SMCRv1 has a similar issue to SMCRv2 (see link below) that may access
> invalid MRs of RMBs when construct LLC ADD LINK CONT messages.
> 
>  BUG: kernel NULL pointer dereference, address: 0000000000000014
>  #PF: supervisor read access in kernel mode
>  #PF: error_code(0x0000) - not-present page
>  PGD 0 P4D 0
>  Oops: 0000 [#1] PREEMPT SMP PTI
>  CPU: 5 PID: 48 Comm: kworker/5:0 Kdump: loaded Tainted: G W   E      6.4.0-rc3+ #49
>  Workqueue: events smc_llc_add_link_work [smc]
>  RIP: 0010:smc_llc_add_link_cont+0x160/0x270 [smc]
>  RSP: 0018:ffffa737801d3d50 EFLAGS: 00010286
>  RAX: ffff964f82144000 RBX: ffffa737801d3dd8 RCX: 0000000000000000
>  RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff964f81370c30
>  RBP: ffffa737801d3dd4 R08: ffff964f81370000 R09: ffffa737801d3db0
>  R10: 0000000000000001 R11: 0000000000000060 R12: ffff964f82e70000
>  R13: ffff964f81370c38 R14: ffffa737801d3dd3 R15: 0000000000000001
>  FS:  0000000000000000(0000) GS:ffff9652bfd40000(0000) knlGS:0000000000000000
>  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>  CR2: 0000000000000014 CR3: 000000008fa20004 CR4: 00000000003706e0
>  DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>  DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>  Call Trace:
>   <TASK>
>   smc_llc_srv_rkey_exchange+0xa7/0x190 [smc]
>   smc_llc_srv_add_link+0x3ae/0x5a0 [smc]
>   smc_llc_add_link_work+0xb8/0x140 [smc]
>   process_one_work+0x1e5/0x3f0
>   worker_thread+0x4d/0x2f0
>   ? __pfx_worker_thread+0x10/0x10
>   kthread+0xe5/0x120
>   ? __pfx_kthread+0x10/0x10
>   ret_from_fork+0x2c/0x50
>   </TASK>
> 
> When an alernate RNIC is available in system, SMC will try to add a new
> link based on the RNIC for resilience. All the RMBs in use will be mapped
> to the new link. Then the RMBs' MRs corresponding to the new link will
> be filled into LLC messages. For SMCRv1, they are ADD LINK CONT messages.
> 
> However smc_llc_add_link_cont() may mistakenly access to unused RMBs which
> haven't been mapped to the new link and have no valid MRs, thus causing a
> crash. So this patch fixes it.
> 
> Fixes: 87f88cda2128 ("net/smc: rkey processing for a new link as SMC client")
> Link: https://lore.kernel.org/r/[email-masked]
> Signed-off-by: Wen Gu <[email-masked]>

This SGTM, thanks.

Reviewed-by: Tony Lu <[email-masked]>

> ---
>  net/smc/smc_llc.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/net/smc/smc_llc.c b/net/smc/smc_llc.c
> index 7a8d916..90f0b60 100644
> --- a/net/smc/smc_llc.c
> +++ b/net/smc/smc_llc.c
> @@ -851,6 +851,8 @@ static int smc_llc_add_link_cont(struct smc_link *link,
>  	addc_llc->num_rkeys = *num_rkeys_todo;
>  	n = *num_rkeys_todo;
>  	for (i = 0; i < min_t(u8, n, SMC_LLC_RKEYS_PER_CONT_MSG); i++) {
> +		while (*buf_pos && !(*buf_pos)->used)
> +			*buf_pos = smc_llc_get_next_rmb(lgr, buf_lst, *buf_pos);
>  		if (!*buf_pos) {
>  			addc_llc->num_rkeys = addc_llc->num_rkeys -
>  					      *num_rkeys_todo;
> @@ -867,8 +869,6 @@ static int smc_llc_add_link_cont(struct smc_link *link,
>  
>  		(*num_rkeys_todo)--;
>  		*buf_pos = smc_llc_get_next_rmb(lgr, buf_lst, *buf_pos);
> -		while (*buf_pos && !(*buf_pos)->used)
> -			*buf_pos = smc_llc_get_next_rmb(lgr, buf_lst, *buf_pos);
>  	}
>  	addc_llc->hd.common.llc_type = SMC_LLC_ADD_LINK_CONT;
>  	addc_llc->hd.length = sizeof(struct smc_llc_msg_add_link_cont);
> -- 
> 1.8.3.1