Re: WARNING in kcm_exit_net (3)

[Kirill Tkhai]

On 31.05.2018 11:16, syzbot wrote:
> Hello,
> 
> syzbot found the following crash on:
> 
> HEAD commit:ÂÂÂ d60d61f36b8f Merge branch 'for-linus' of git://git.kernel...
> git tree:ÂÂÂÂÂÂ upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=101bb52f800000
> kernel config:Â https://syzkaller.appspot.com/x/.config?x=968b0b23c7854c0b
> dashboard link: https://syzkaller.appspot.com/bug?extid=5f1a04e374a635efc426
> compiler:ÂÂÂÂÂÂ gcc (GCC) 8.0.1 20180413 (experimental)
> syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=13b9ed2f800000
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+5f1a04e374a635efc426@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> IPVS: ftp: loaded support on port[0] = 21
> IPVS: ftp: loaded support on port[0] = 21
> IPVS: ftp: loaded support on port[0] = 21
> IPVS: ftp: loaded support on port[0] = 21
> IPVS: ftp: loaded support on port[0] = 21
> WARNING: CPU: 0 PID: 6 at net/kcm/kcmsock.c:2023 kcm_exit_net+0x392/0x3e0 net/kcm/kcmsock.c:2023
> Kernel panic - not syncing: panic_on_warn set ...
> 
> CPU: 0 PID: 6 Comm: kworker/u4:0 Not tainted 4.17.0-rc7+ #75
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Workqueue: netns cleanup_net
> Call Trace:
> Â__dump_stack lib/dump_stack.c:77 [inline]
> Âdump_stack+0x1b9/0x294 lib/dump_stack.c:113
> Âpanic+0x22f/0x4de kernel/panic.c:184
> Â__warn.cold.8+0x163/0x1b3 kernel/panic.c:536
> Âreport_bug+0x252/0x2d0 lib/bug.c:186
> Âfixup_bug arch/x86/kernel/traps.c:178 [inline]
> Âdo_error_trap+0x1de/0x490 arch/x86/kernel/traps.c:296
> Âdo_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:315
> Âinvalid_op+0x14/0x20 arch/x86/entry/entry_64.S:992
> RIP: 0010:kcm_exit_net+0x392/0x3e0 net/kcm/kcmsock.c:2023
> RSP: 0018:ffff8801d9a97430 EFLAGS: 00010293
> RAX: ffff8801d9a88180 RBX: 1ffff1003b352e86 RCX: 1ffff1003b351135
> RDX: 0000000000000000 RSI: ffffffff86d56942 RDI: 0000000000000286
> RBP: ffff8801d9a974f8 R08: 1ffff1003b352e67 R09: ffffed003b5c46d2
> R10: 0000000000000003 R11: 0000000000000003 R12: 1ffff1003b352e8a
> R13: ffff8801d9a974d0 R14: ffff8801d96763d0 R15: ffff8801c51d0e00
> Âops_exit_list.isra.7+0xb0/0x160 net/core/net_namespace.c:152
> Âcleanup_net+0x51d/0xb20 net/core/net_namespace.c:523
> Âprocess_one_work+0xc1e/0x1b50 kernel/workqueue.c:2145
> Âworker_thread+0x1cc/0x1440 kernel/workqueue.c:2279
> Âkthread+0x345/0x410 kernel/kthread.c:240
> Âret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:412
> Dumping ftrace buffer:
> ÂÂ (ftrace buffer empty)
> Kernel Offset: disabled
> Rebooting in 86400 seconds..

How about this?

[PATCH]kcm: Fix use-after-free caused by clonned sockets

kcm_clone() creates kernel socket, which does not take net counter.
Thus, the net may die before the socket is completely destructed,
i.e. kcm_exit_net() is executed before kcm_done().

Reported-by: syzbot+5f1a04e374a635efc426@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Kirill Tkhai <ktkhai@xxxxxxxxxxxxx>
---
diff --git a/net/kcm/kcmsock.c b/net/kcm/kcmsock.c
index d67734c99027..84b7d5c6fec8 100644
--- a/net/kcm/kcmsock.c
+++ b/net/kcm/kcmsock.c
@@ -1671,7 +1671,7 @@ static struct file *kcm_clone(struct socket *osock)
 	__module_get(newsock->ops->owner);
 
 	newsk = sk_alloc(sock_net(osock->sk), PF_KCM, GFP_KERNEL,
-			 &kcm_proto, true);
+			 &kcm_proto, false);
 	if (!newsk) {
 		sock_release(newsock);
 		return ERR_PTR(-ENOMEM);