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

D. Wythe
2025-04-02T07:20:18Z

On Wed, Apr 02, 2025 at 10:37:24AM +0800, Wang Liang wrote:
>
> 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.
>

This is actually because the current smc_sock is not an inet_sock,
leading to two modules simultaneously modifying the same offset in
memory but interpreting its structure differently. I previously proposed
embedding an inet(6)_sock at the beginning of smc_sock, but the
community had some objections...

I'm not sure on the community's current stance on this matter, but if a
fix is absolutely necessary, my recommendation would still be to embed
an inet(6)_sock within the smc_sock structure

D.

> >

> >/P
> >
> >