[PATCH] can: af_can: Fix possible NULL pointer dereference in can_exit

[Yue Haibing]

From: YueHaibing <yuehaibing@xxxxxxxxxx>

Syzkaller report this:

kasan: GPF could be caused by NULL-ptr deref or user memory access
general protection fault: 0000 [#1] SMP KASAN PTI
CPU: 0 PID: 9400 Comm: syz-executor.0 Tainted: G         C        5.0.0-rc8+ #3
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1 04/01/2014
RIP: 0010:__list_del include/linux/list.h:105 [inline]
RIP: 0010:__list_del_entry include/linux/list.h:120 [inline]
RIP: 0010:list_del include/linux/list.h:125 [inline]
RIP: 0010:__unregister_pernet_operations net/core/net_namespace.c:1075 [inline]
RIP: 0010:unregister_pernet_operations+0x124/0x540 net/core/net_namespace.c:1137
Code: 89 c1 48 c1 e9 03 80 3c 11 00 0f 85 38 03 00 00 48 8d 7d 08 48 ba 00 00 00 00 00 fc ff df 4d 8b 7c 24 08 48 89 f9 48 c1 e9 03 <80> 3c 11 00 0f 85 02 03 00 00 48 8d 9c 24 b8 00 00 00 48 ba 00 00
RSP: 0018:ffff8881b871fbb0 EFLAGS: 00010a06
RAX: ffffffffc198c4c8 RBX: dffffc0000000000 RCX: 1bd5a00000000021
RDX: dffffc0000000000 RSI: ffffc900014c4000 RDI: dead000000000108
RBP: dead000000000100 R08: 0000000000000001 R09: 0000000000000000
R10: ffff8881b871fb30 R11: 0000000000000000 R12: ffffffffc198c4c0
R13: ffff8881b871fbe8 R14: 1ffff110370e3f79 R15: dead000000000200
FS:  00007f029df32700(0000) GS:ffff8881f7000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffc85454218 CR3: 00000001e0ff4004 CR4: 00000000007606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
PKRU: 55555554
Call Trace:
 unregister_pernet_subsys+0x1d/0x30 net/core/net_namespace.c:1184
 can_exit+0x3f/0x56 [can]
 __do_sys_delete_module kernel/module.c:1018 [inline]
 __se_sys_delete_module kernel/module.c:961 [inline]
 __x64_sys_delete_module+0x3dc/0x5e0 kernel/module.c:961
 do_syscall_64+0x147/0x600 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x462e99
Code: f7 d8 64 89 02 b8 ff ff ff ff c3 66 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 bc ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f029df31c58 EFLAGS: 00000246 ORIG_RAX: 00000000000000b0
RAX: ffffffffffffffda RBX: 000000000073bf00 RCX: 0000000000462e99
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00000000200000c0
RBP: 0000000000000002 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f029df326bc
R13: 00000000004bcca9 R14: 00000000006f6b48 R15: 00000000ffffffff

register_pernet_subsys may fails in can_init,then can_exit calls
unregister_pernet_subsys when unloading, it can trigger a NULL
pointer dereference while doing list_del.This patch fix error
cleanup path of can_init to avoid this.

Reported-by: Hulk Robot <hulkci@xxxxxxxxxx>
Signed-off-by: YueHaibing <yuehaibing@xxxxxxxxxx>
---
 net/can/af_can.c | 24 +++++++++++++++++++++---
 1 file changed, 21 insertions(+), 3 deletions(-)

diff --git a/net/can/af_can.c b/net/can/af_can.c
index 1684ba5..5d75685 100644
--- a/net/can/af_can.c
+++ b/net/can/af_can.c
@@ -958,6 +958,8 @@ static struct pernet_operations can_pernet_ops __read_mostly = {
 
 static __init int can_init(void)
 {
+	int rc;
+
 	/* check for correct padding to be able to use the structs similarly */
 	BUILD_BUG_ON(offsetof(struct can_frame, can_dlc) !=
 		     offsetof(struct canfd_frame, len) ||
@@ -971,15 +973,31 @@ static __init int can_init(void)
 	if (!rcv_cache)
 		return -ENOMEM;
 
-	register_pernet_subsys(&can_pernet_ops);
+	rc = register_pernet_subsys(&can_pernet_ops);
+	if (rc)
+		goto free_cache;
 
 	/* protocol register */
-	sock_register(&can_family_ops);
-	register_netdevice_notifier(&can_netdev_notifier);
+	rc = sock_register(&can_family_ops);
+	if (rc)
+		goto unregister_pernet;
+
+	rc = register_netdevice_notifier(&can_netdev_notifier);
+	if (rc)
+		goto sock_unregister;
+
 	dev_add_pack(&can_packet);
 	dev_add_pack(&canfd_packet);
 
 	return 0;
+
+sock_unregister:
+	sock_unregister(PF_CAN);
+unregister_pernet:
+	unregister_pernet_subsys(&can_pernet_ops);
+free_cache:
+	kmem_cache_destroy(rcv_cache);
+	return rc;
 }
 
 static __exit void can_exit(void)
-- 
2.7.0