Re: [PATCH net] net/smc: reject CHID-0 ACCEPT that matches an empty ism_dev slot

[Paolo Abeni <pabeni@redhat.com>]

On 5/11/26 8:21 AM, Xiang Mei wrote:
> On the SMC-D client, slot 0 of ini->ism_dev[]/ini->ism_chid[] is
> reserved for an SMC-Dv1 device. smc_find_ism_v2_device_clnt()
> populates V2 entries starting at index 1, so when no V1 device is
> selected slot 0 is left in its kzalloc()'ed state with ism_dev[0] ==
> NULL and ism_chid[0] == 0.
> 
> smc_v2_determine_accepted_chid() then matches the peer's CHID against
> the array starting from index 0 using the CHID alone. A malicious
> peer replying to a SMC-Dv2-only proposal with d1.chid == 0 matches
> the empty slot, ini->ism_selected becomes 0, and the subsequent
> ism_dev[0]->lgr_lock dereference in smc_conn_create() faults at
> offsetof(struct smcd_dev, lgr_lock) == 0x68:
> 
>   BUG: KASAN: null-ptr-deref in _raw_spin_lock_bh+0x79/0xe0
>   Write of size 4 at addr 0000000000000068 by task exploit/144
>   Call Trace:
>    _raw_spin_lock_bh
>    smc_conn_create (net/smc/smc_core.c:1997)
>    __smc_connect (net/smc/af_smc.c:1447)
>    smc_connect (net/smc/af_smc.c:1720)
>    __sys_connect
>    __x64_sys_connect
>    do_syscall_64
> 
> Require ism_dev[i] to be non-NULL before accepting a CHID match.
> 
> Fixes: a7c9c5f4af7f ("net/smc: CLC accept / confirm V2")
> Reported-by: Weiming Shi <bestswngs@gmail.com>
> Assisted-by: Claude:claude-opus-4-7
> Signed-off-by: Xiang Mei <xmei5@asu.edu>
> ---
>  net/smc/af_smc.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
> index 185dbed7de5d..12ea3b6dbc64 100644
> --- a/net/smc/af_smc.c
> +++ b/net/smc/af_smc.c
> @@ -1400,7 +1400,8 @@ smc_v2_determine_accepted_chid(struct smc_clc_msg_accept_confirm *aclc,
>  	int i;
>  
>  	for (i = 0; i < ini->ism_offered_cnt + 1; i++) {
> -		if (ini->ism_chid[i] == ntohs(aclc->d1.chid)) {
> +		if (ini->ism_dev[i] &&
> +		    ini->ism_chid[i] == ntohs(aclc->d1.chid)) {
>  			ini->ism_selected = i;
>  			return 0;
>  		}

Patch LGTM, thanks!

@smc maintainers, please note that sashiko reviews:

https://sashiko.dev/#/patchset/20260511062138.2839584-1-xmei5%40asu.edu

pointed to another pre-existing issue in this area you may want to address.

/P