[PATCH 5.0 011/117] kcm: switch order of device registration to fix a crash

Greg Kroah-Hartman
2019-04-15T19:10:01Z

[ Upstream commit 3c446e6f96997f2a95bf0037ef463802162d2323 ]

When kcm is loaded while many processes try to create a KCM socket, a
crash occurs:
BUG: unable to handle kernel NULL pointer dereference at 000000000000000e
IP: mutex_lock+0x27/0x40 kernel/locking/mutex.c:240
PGD 8000000016ef2067 P4D 8000000016ef2067 PUD 3d6e9067 PMD 0
Oops: 0002 [#1] SMP KASAN PTI
CPU: 0 PID: 7005 Comm: syz-executor.5 Not tainted 4.12.14-396-default #1 SLE15-SP1 (unreleased)
RIP: 0010:mutex_lock+0x27/0x40 kernel/locking/mutex.c:240
RSP: 0018:ffff88000d487a00 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 000000000000000e RCX: 1ffff100082b0719
...
CR2: 000000000000000e CR3: 000000004b1bc003 CR4: 0000000000060ef0
Call Trace:
kcm_create+0x600/0xbf0 [kcm]
__sock_create+0x324/0x750 net/socket.c:1272
...

This is due to race between sock_create and unfinished
register_pernet_device. kcm_create tries to do "net_generic(net,
kcm_net_id)". but kcm_net_id is not initialized yet.

So switch the order of the two to close the race.

This can be reproduced with mutiple processes doing socket(PF_KCM, ...)
and one process doing module removal.

Fixes: ab7ac4eb9832 ("kcm: Kernel Connection Multiplexor module")
Reviewed-by: Michal Kubecek <mkubecek@suse.cz>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/kcm/kcmsock.c | 16 ++++++++--------
1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/net/kcm/kcmsock.c b/net/kcm/kcmsock.c
index 571d824e4e24..b919db02c7f9 100644
--- a/net/kcm/kcmsock.c
+++ b/net/kcm/kcmsock.c
@@ -2054,14 +2054,14 @@ static int __init kcm_init(void)
if (err)
goto fail;

- err = sock_register(&kcm_family_ops);
- if (err)
- goto sock_register_fail;
-
err = register_pernet_device(&kcm_net_ops);
if (err)
goto net_ops_fail;

+ err = sock_register(&kcm_family_ops);
+ if (err)
+ goto sock_register_fail;
+
err = kcm_proc_init();
if (err)
goto proc_init_fail;
@@ -2069,12 +2069,12 @@ static int __init kcm_init(void)
return 0;

proc_init_fail:
- unregister_pernet_device(&kcm_net_ops);
-
-net_ops_fail:
sock_unregister(PF_KCM);

sock_register_fail:
+ unregister_pernet_device(&kcm_net_ops);
+
+net_ops_fail:
proto_unregister(&kcm_proto);

fail:
@@ -2090,8 +2090,8 @@ static int __init kcm_init(void)
static void __exit kcm_exit(void)
{
kcm_proc_exit();
- unregister_pernet_device(&kcm_net_ops);
sock_unregister(PF_KCM);
+ unregister_pernet_device(&kcm_net_ops);
proto_unregister(&kcm_proto);
destroy_workqueue(kcm_wq);

--
2.19.1