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

[Wenjia Zhang <wenjia@linux.ibm.com>]

On 31.03.25 10:10, Wang Liang wrote:
> Syzbot reported a general protection fault:
> 
>    CPU: 0 UID: 0 PID: 5830 Comm: syz-executor600 Not tainted 6.14.0-rc4-syzkaller-00090-gdd83757f6e68 #0
>    RIP: 0010:smc_diag_msg_common_fill net/smc/smc_diag.c:44 [inline]
>    RIP: 0010:__smc_diag_dump.constprop.0+0x3de/0x23d0 net/smc/smc_diag.c:89
>    Call Trace:
>     <TASK>
>     smc_diag_dump_proto+0x26d/0x420 net/smc/smc_diag.c:217
>     smc_diag_dump+0x84/0x90 net/smc/smc_diag.c:236
>     netlink_dump+0x53c/0xd00 net/netlink/af_netlink.c:2318
>     __netlink_dump_start+0x6ca/0x970 net/netlink/af_netlink.c:2433
>     netlink_dump_start include/linux/netlink.h:340 [inline]
>     smc_diag_handler_dump+0x1fb/0x240 net/smc/smc_diag.c:251
>     __sock_diag_cmd net/core/sock_diag.c:249 [inline]
>     sock_diag_rcv_msg+0x437/0x790 net/core/sock_diag.c:287
>     netlink_rcv_skb+0x16b/0x440 net/netlink/af_netlink.c:2543
>     netlink_unicast_kernel net/netlink/af_netlink.c:1322 [inline]
>     netlink_unicast+0x53c/0x7f0 net/netlink/af_netlink.c:1348
>     netlink_sendmsg+0x8b8/0xd70 net/netlink/af_netlink.c:1892
>     sock_sendmsg_nosec net/socket.c:718 [inline]
>     __sock_sendmsg net/socket.c:733 [inline]
>     ____sys_sendmsg+0xaaf/0xc90 net/socket.c:2573
>     ___sys_sendmsg+0x135/0x1e0 net/socket.c:2627
>     __sys_sendmsg+0x16e/0x220 net/socket.c:2659
>     do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>     do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
>     entry_SYSCALL_64_after_hwframe+0x77/0x7f
>     </TASK>
> 
> When create smc socket, smc_inet_init_sock() first add sk to the smc_hash
> by smc_hash_sk(), then create smc->clcsock. it is possible that, after
> smc_diag_dump_proto() traverses the smc_hash, smc->clcsock is not created
> when the function visit it.
> 
> The process like this:
> 
>    (CPU1)                         | (CPU2)
>    inet6_create()                 |
>      smc_inet_init_sock()         |
>        smc_sk_init()              |
>          smc_hash_sk()            |
>            head = &smc_hash->ht;  |
>            sk_add_node(sk, head); |
>                                   | smc_diag_dump_proto
>                                   |   head = &smc_hash->ht;
>                                   |     sk_for_each(sk, head)
>                                   |       __smc_diag_dump()
>                                   |         visit smc->clcsock
>        smc_create_clcsk()         |
>            set smc->clcsock       |
> 
> Fix this by initialize smc->clcsock to NULL before add sk to smc_hash in
> smc_sk_init().
> 
> Reported-by: syzbot+271fed3ed6f24600c364@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=271fed3ed6f24600c364
> Fixes: f16a7dd5cf27 ("smc: netlink interface for SMC sockets")
> Signed-off-by: Wang Liang <wangliang74@huawei.com>
> ---
>   net/smc/af_smc.c | 1 +
>   1 file changed, 1 insertion(+)
> 
> 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);

I have to agree with this workaround, even though I see that is not the 
best solution. Thus, I'd like to give my R-b:

Reviewed-by: Wenjia Zhang <wenjia@linux.ibm.com>

Btw. @D. Wythe, would you mind sending me the link of your proposal you 
mentioned please? Let me have a look. It seems like I missed it.

Thanks,
Wenjia