[syzbot] possible deadlock in kcm_ioctl

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 95d10484d66e Add linux-next specific files for 20220817
git tree: linux-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=11b3b2f3080000
kernel config: https://syzkaller.appspot.com/x/.config?x=2f5fa747986be53a
dashboard link: https://syzkaller.appspot.com/bug?extid=e696806ef96cdd2d87cd
compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1778e50d080000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1379e5e3080000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+e69680...@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
6.0.0-rc1-next-20220817-syzkaller #0 Not tainted
------------------------------------------------------
syz-executor769/3613 is trying to acquire lock:
ffff88801cb5c0f8 ((work_completion)(&strp->work)){+.+.}-{0:0}, at: __flush_work+0xdd/0xae0 kernel/workqueue.c:3066

but task is already holding lock:
ffff88801d5b0fb0 (sk_lock-AF_INET6){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1687 [inline]
ffff88801d5b0fb0 (sk_lock-AF_INET6){+.+.}-{0:0}, at: kcm_attach net/kcm/kcmsock.c:1390 [inline]
ffff88801d5b0fb0 (sk_lock-AF_INET6){+.+.}-{0:0}, at: kcm_attach_ioctl net/kcm/kcmsock.c:1490 [inline]
ffff88801d5b0fb0 (sk_lock-AF_INET6){+.+.}-{0:0}, at: kcm_ioctl+0x396/0x1180 net/kcm/kcmsock.c:1696

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (sk_lock-AF_INET6){+.+.}-{0:0}:
lock_sock_nested+0x36/0xf0 net/core/sock.c:3391
do_strp_work net/strparser/strparser.c:398 [inline]
strp_work+0x40/0x130 net/strparser/strparser.c:415
process_one_work+0x991/0x1610 kernel/workqueue.c:2289
worker_thread+0x665/0x1080 kernel/workqueue.c:2436
kthread+0x2e4/0x3a0 kernel/kthread.c:376
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:306

-> #0 ((work_completion)(&strp->work)){+.+.}-{0:0}:
check_prev_add kernel/locking/lockdep.c:3095 [inline]
check_prevs_add kernel/locking/lockdep.c:3214 [inline]
validate_chain kernel/locking/lockdep.c:3829 [inline]
__lock_acquire+0x2a43/0x56d0 kernel/locking/lockdep.c:5053
lock_acquire kernel/locking/lockdep.c:5666 [inline]
lock_acquire+0x1ab/0x570 kernel/locking/lockdep.c:5631
__flush_work+0x105/0xae0 kernel/workqueue.c:3069
__cancel_work_timer+0x3f9/0x570 kernel/workqueue.c:3160
strp_done+0x64/0xf0 net/strparser/strparser.c:513
kcm_attach net/kcm/kcmsock.c:1429 [inline]
kcm_attach_ioctl net/kcm/kcmsock.c:1490 [inline]
kcm_ioctl+0x913/0x1180 net/kcm/kcmsock.c:1696
sock_do_ioctl+0xcc/0x230 net/socket.c:1169
sock_ioctl+0x2f1/0x640 net/socket.c:1286
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:870 [inline]
__se_sys_ioctl fs/ioctl.c:856 [inline]
__x64_sys_ioctl+0x193/0x200 fs/ioctl.c:856
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd

other info that might help us debug this:

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(sk_lock-AF_INET6);
lock((work_completion)(&strp->work));
lock(sk_lock-AF_INET6);
lock((work_completion)(&strp->work));

*** DEADLOCK ***

1 lock held by syz-executor769/3613:
#0: ffff88801d5b0fb0 (sk_lock-AF_INET6){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1687 [inline]
#0: ffff88801d5b0fb0 (sk_lock-AF_INET6){+.+.}-{0:0}, at: kcm_attach net/kcm/kcmsock.c:1390 [inline]
#0: ffff88801d5b0fb0 (sk_lock-AF_INET6){+.+.}-{0:0}, at: kcm_attach_ioctl net/kcm/kcmsock.c:1490 [inline]
#0: ffff88801d5b0fb0 (sk_lock-AF_INET6){+.+.}-{0:0}, at: kcm_ioctl+0x396/0x1180 net/kcm/kcmsock.c:1696

stack backtrace:
CPU: 0 PID: 3613 Comm: syz-executor769 Not tainted 6.0.0-rc1-next-20220817-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/22/2022
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
check_noncircular+0x25f/0x2e0 kernel/locking/lockdep.c:2175
check_prev_add kernel/locking/lockdep.c:3095 [inline]
check_prevs_add kernel/locking/lockdep.c:3214 [inline]
validate_chain kernel/locking/lockdep.c:3829 [inline]
__lock_acquire+0x2a43/0x56d0 kernel/locking/lockdep.c:5053
lock_acquire kernel/locking/lockdep.c:5666 [inline]
lock_acquire+0x1ab/0x570 kernel/locking/lockdep.c:5631
__flush_work+0x105/0xae0 kernel/workqueue.c:3069
__cancel_work_timer+0x3f9/0x570 kernel/workqueue.c:3160
strp_done+0x64/0xf0 net/strparser/strparser.c:513
kcm_attach net/kcm/kcmsock.c:1429 [inline]
kcm_attach_ioctl net/kcm/kcmsock.c:1490 [inline]
kcm_ioctl+0x913/0x1180 net/kcm/kcmsock.c:1696
sock_do_ioctl+0xcc/0x230 net/socket.c:1169
sock_ioctl+0x2f1/0x640 net/socket.c:1286
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:870 [inline]
__se_sys_ioctl fs/ioctl.c:856 [inline]
__x64_sys_ioctl+0x193/0x200 fs/ioctl.c:856
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7fc907a73f09
Code: 28 c3 e8 2a 14 00 00 66 2e 0f 1f 84 00 00 00 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 c0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffc5f76b0d8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fc907a73f09
RDX: 00000000200000c0 RSI: 00000000000089e0 RDI: 0000000000000003


---
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https://goo.gl/tpsmEJ#testing-patches

[Hillf Danton]

On Sat, 20 Aug 2022 23:24:28 -0700

> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: 95d10484d66e Add linux-next specific files for 20220817
> git tree: linux-next
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=11b3b2f3080000
> kernel config: https://syzkaller.appspot.com/x/.config?x=2f5fa747986be53a
> dashboard link: https://syzkaller.appspot.com/bug?extid=e696806ef96cdd2d87cd
> compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1778e50d080000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1379e5e3080000

Stop parser after releasing sock.

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git 95d10484d66e

--- a/net/kcm/kcmsock.c 2022-08-21 19:03:53.088383700 +0800
+++ b/net/kcm/kcmsock.c 2022-08-21 19:23:43.935799700 +0800
@@ -1425,11 +1425,11 @@ static int kcm_attach(struct socket *soc
*/
if (csk->sk_user_data) {
write_unlock_bh(&csk->sk_callback_lock);
+ release_sock(csk);
strp_stop(&psock->strp);
strp_done(&psock->strp);
kmem_cache_free(kcm_psockp, psock);
- err = -EALREADY;
- goto out;
+ return -EALREADY;
}

psock->save_data_ready = csk->sk_data_ready;
--

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-and-tested-by: syzbot+e69680...@syzkaller.appspotmail.com

Tested on:

commit: 95d10484 Add linux-next specific files for 20220817
git tree: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
console output: https://syzkaller.appspot.com/x/log.txt?x=16cc63d3080000

kernel config: https://syzkaller.appspot.com/x/.config?x=2f5fa747986be53a
dashboard link: https://syzkaller.appspot.com/bug?extid=e696806ef96cdd2d87cd
compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2

patch: https://syzkaller.appspot.com/x/patch.diff?x=16cac9cb080000

Note: testing is done by a robot and is best-effort only.