Subject: Re: [PATCH net] net/smc: Initialize smc hashtables before registering users

From: Dust Li <[email-masked]>
Date: Wed, 17 Dec 2025 23:25:38 +0800

On 2025-12-17 12:48:19, Alexandra Winter wrote:
>During initialisation of the SMC module initialize smc_v4/6_hashinfo before
>calling smc_nl_init(), proto_register() or sock_register(), to avoid a race
>that can cause use of an uninitialised pointer in case an smc protocol is
>called before the module is done initialising.
>
>syzbot report:
>KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
>Call Trace:
> <TASK>
> smc_diag_dump+0x59/0xa0 net/smc/smc_diag.c:236
> netlink_dump+0x647/0xd80 net/netlink/af_netlink.c:2325
> __netlink_dump_start+0x59f/0x780 net/netlink/af_netlink.c:2440
> netlink_dump_start include/linux/netlink.h:339 [inline]
> smc_diag_handler_dump+0x1ab/0x250 net/smc/smc_diag.c:251
> sock_diag_rcv_msg+0x3dc/0x5f0
> netlink_rcv_skb+0x1e3/0x430 net/netlink/af_netlink.c:2550
> netlink_unicast_kernel net/netlink/af_netlink.c:1331 [inline]
> netlink_unicast+0x7f0/0x990 net/netlink/af_netlink.c:1357
> netlink_sendmsg+0x8e4/0xcb0 net/netlink/af_netlink.c:1901

I don't think this is related to smc_nl_init().

Here the calltrace is smc_diag_dump(), which was registered in
sock_diag_register(&smc_diag_handler).

But smc_nl_init() is registering the general netlink in SMC,
which is unrelated to smc_diag_dump().

I think the root cause should be related to the initializing between
smc_diag.ko and smc_v4/6_hashinfo.ht.
The change in your previous patch 'dibs: Register smc as dibs_client'
may change the possiblity to this bug.

Best regards,
Dust

>
>Fixes: f16a7dd5cf27 ("smc: netlink interface for SMC sockets")
>Reported-by: [email-masked]
>Closes: https://syzkaller.appspot.com/bug?extid=f69bfae0a4eb29976e44
>Signed-off-by: Alexandra Winter <[email-masked]>
>---
> net/smc/af_smc.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
>diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
>index f97f77b041d9..b0f4405fb714 100644
>--- a/net/smc/af_smc.c
>+++ b/net/smc/af_smc.c
>@@ -3524,6 +3524,9 @@ static int __init smc_init(void)
> 		goto out_pernet_subsys_stat;
> 	smc_clc_init();
> 
>+	INIT_HLIST_HEAD(&smc_v4_hashinfo.ht);
>+	INIT_HLIST_HEAD(&smc_v6_hashinfo.ht);
>+
> 	rc = smc_nl_init();
> 	if (rc)
> 		goto out_ism;
>@@ -3581,8 +3584,6 @@ static int __init smc_init(void)
> 		pr_err("%s: sock_register fails with %d\n", __func__, rc);
> 		goto out_proto6;
> 	}
>-	INIT_HLIST_HEAD(&smc_v4_hashinfo.ht);
>-	INIT_HLIST_HEAD(&smc_v6_hashinfo.ht);
> 
> 	rc = smc_ib_register_client();
> 	if (rc) {
>-- 
>2.51.0