Re: [PATCH net] net/smc: Initialize smc hashtables before registering users

[Dust Li <dust.li@linux.alibaba.com>]

On 2025-12-22 10:50:37, Alexandra Winter wrote:
>
>
>On 17.12.25 16:25, Dust Li wrote:
>> On 2025-12-17 12:48:19, Alexandra Winter wrote:
>>> During initialisation of the SMC module initialize smc_v4/6_hashinfo before
>>> calling smc_nl_init(), proto_register() or sock_register(), to avoid a race
>>> that can cause use of an uninitialised pointer in case an smc protocol is
>>> called before the module is done initialising.
>>>
>>> syzbot report:
>>> KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
>>> Call Trace:
>>> <TASK>
>>> smc_diag_dump+0x59/0xa0 net/smc/smc_diag.c:236
>>> netlink_dump+0x647/0xd80 net/netlink/af_netlink.c:2325
>>> __netlink_dump_start+0x59f/0x780 net/netlink/af_netlink.c:2440
>>> netlink_dump_start include/linux/netlink.h:339 [inline]
>>> smc_diag_handler_dump+0x1ab/0x250 net/smc/smc_diag.c:251
>>> sock_diag_rcv_msg+0x3dc/0x5f0
>>> netlink_rcv_skb+0x1e3/0x430 net/netlink/af_netlink.c:2550
>>> netlink_unicast_kernel net/netlink/af_netlink.c:1331 [inline]
>>> netlink_unicast+0x7f0/0x990 net/netlink/af_netlink.c:1357
>>> netlink_sendmsg+0x8e4/0xcb0 net/netlink/af_netlink.c:1901
>> 
>> I don't think this is related to smc_nl_init().
>> 
>> Here the calltrace is smc_diag_dump(), which was registered in
>> sock_diag_register(&smc_diag_handler).
>> 
>> But smc_nl_init() is registering the general netlink in SMC,
>> which is unrelated to smc_diag_dump().
>
>
>I had assumed some dependency between the smc netlink diag socket and smc_nl_init()
>and wrongly assumed that the smc_diag_init() and smc_init() could race.
>I now understand that modprobe will ensure smc_diag_init() is called before smc_init(),
>so you are right: this patch is indeed NOT a fix for this sysbot report [1]
>
>
>> I think the root cause should be related to the initializing between
>> smc_diag.ko and smc_v4/6_hashinfo.ht.
>
>Given modprobe initializes the modules sequentially, I do not see how these could race.
>
>I guess this syszbot report was fixed by
>f584239a9ed2 ("net/smc: fix general protection fault in __smc_diag_dump")
>as reported in [2] .
>
>I'm not sure about the correct procedure, if nobody recommends a better action, I'll send a
>
>#syz dup: general protection fault in __smc_diag_dump
>to
>syzbot+f69bfae0a4eb29976e44@syzkaller.appspotmail.com
>(this one: general protection fault in smc_diag_dump_proto [1])
>
>
>I still think initializing the hashtables before smc_nl_init()
>makes sense. I'll resend this patch without mentioning syzbot.

Agree.

Best regards,
Dust