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

Wenjia Zhang
2025-04-03T11:55:26Z

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