Re: [PATCH net] net/smc: fix general protection fault in __smc_diag_dump

[Wang Liang <wangliang74@huawei.com>]

在 2025/4/1 19:01, Paolo Abeni 写道:
> On 3/31/25 10:10 AM, Wang Liang wrote:
>> diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
>> index 3e6cb35baf25..454801188514 100644
>> --- a/net/smc/af_smc.c
>> +++ b/net/smc/af_smc.c
>> @@ -371,6 +371,7 @@ void smc_sk_init(struct net *net, struct sock *sk, int protocol)
>>   	sk->sk_protocol = protocol;
>>   	WRITE_ONCE(sk->sk_sndbuf, 2 * READ_ONCE(net->smc.sysctl_wmem));
>>   	WRITE_ONCE(sk->sk_rcvbuf, 2 * READ_ONCE(net->smc.sysctl_rmem));
>> +	smc->clcsock = NULL;
>>   	INIT_WORK(&smc->tcp_listen_work, smc_tcp_listen_work);
>>   	INIT_WORK(&smc->connect_work, smc_connect_work);
>>   	INIT_DELAYED_WORK(&smc->conn.tx_work, smc_tx_work);
> The syzkaller report has a few reproducers, have you tested this? AFAICS
> the smc socket is already zeroed on allocation by sk_alloc().


Yes, I test it by the C repro:
https://syzkaller.appspot.com/text?tag=ReproC&x=13d2dc98580000

The C repro is provided by the 2025/02/27 15:16 crash from
   https://syzkaller.appspot.com/bug?extid=271fed3ed6f24600c364

After apply my patch, the crash no longer happens when running the C repro.

"the smc socket is already zeroed on allocation by sk_alloc()", That is 
right.
However, smc->clcsock may be modified indirectly in inet6_create().
The process like this:

   __sys_socket
     __sys_socket_create
       sock_create
         __sock_create
           # pf->create
           inet6_create
             // init smc->clcsock = 0
             sk = sk_alloc()

             // set smc->clcsock to invalid address
             inet = inet_sk(sk);
             inet_assign_bit(IS_ICSK, sk, INET_PROTOSW_ICSK & answer_flags);
             inet6_set_bit(MC6_LOOP, sk);
             inet6_set_bit(MC6_ALL, sk);

             smc_inet_init_sock
               smc_sk_init
                 // add sk to smc_hash
                 smc_hash_sk
                   sk_add_node(sk, head);
               smc_create_clcsk
                 // set smc->clcsock
                 sock_create_kern(..., &smc->clcsock);)

So initialize smc->clcsock to NULL explicitly in smc_sk_init() can fix
this crash scene. If the problem can be reproduced after this patch, I
guess it is not the same reason, and fix it by another patch is more
appropriate.

>
> /P
>
>