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

Wang Liang
2025-03-31T07:59:57Z

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);
--
2.34.1