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

From: Dust Li <[email-masked]>
Date: Thu, 14 May 2026 19:57:05 +0800

On 2026-05-14 12:19:46, Paolo Abeni wrote:
>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 <[email-masked]>
>> Assisted-by: Claude:claude-opus-4-7
>> Signed-off-by: Xiang Mei <[email-masked]>
>> ---
>>  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

I agree. Apologies, I overlooked your comments prior to replying to
Xiang Mei's patch.

Best regards,
Dust