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

[Alexandra Winter <wintera@linux.ibm.com>]

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

Fixes: f16a7dd5cf27 ("smc: netlink interface for SMC sockets")
Reported-by: syzbot+f69bfae0a4eb29976e44@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=f69bfae0a4eb29976e44
Signed-off-by: Alexandra Winter <wintera@linux.ibm.com>
---
 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