[syzbot] [net?] possible deadlock in unix_notinflight

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 443574b03387 riscv, bpf: Fix kfunc parameters incompatibil..
git tree: bpf
console+strace: https://syzkaller.appspot.com/x/log.txt?x=12898aa9180000
kernel config: https://syzkaller.appspot.com/x/.config?x=6fb1be60a193d440
dashboard link: https://syzkaller.appspot.com/bug?extid=38b3aa8cd529958bd27a
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=13d693e3180000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=11aee305180000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/3f355021a085/disk-443574b0.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/44cf4de7472a/vmlinux-443574b0.xz
kernel image: https://storage.googleapis.com/syzbot-assets/a99a36c7ad65/bzImage-443574b0.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+38b3aa...@syzkaller.appspotmail.com

============================================
WARNING: possible recursive locking detected
6.8.0-syzkaller-05236-g443574b03387 #0 Not tainted
--------------------------------------------
kworker/u8:0/10 is trying to acquire lock:
ffffffff8f48b798 (unix_gc_lock){+.+.}-{2:2}, at: spin_lock include/linux/spinlock.h:351 [inline]
ffffffff8f48b798 (unix_gc_lock){+.+.}-{2:2}, at: unix_notinflight+0x204/0x390 net/unix/garbage.c:140

but task is already holding lock:
ffffffff8f48b798 (unix_gc_lock){+.+.}-{2:2}, at: spin_lock include/linux/spinlock.h:351 [inline]
ffffffff8f48b798 (unix_gc_lock){+.+.}-{2:2}, at: __unix_gc+0x117/0xf10 net/unix/garbage.c:261

other info that might help us debug this:
Possible unsafe locking scenario:

CPU0
----
lock(unix_gc_lock);
lock(unix_gc_lock);

*** DEADLOCK ***

May be due to missing lock nesting notation

3 locks held by kworker/u8:0/10:
#0: ffff888014c81148 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3229 [inline]
#0: ffff888014c81148 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_scheduled_works+0x8e0/0x1770 kernel/workqueue.c:3335
#1: ffffc900000f7d00 (unix_gc_work){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3230 [inline]
#1: ffffc900000f7d00 (unix_gc_work){+.+.}-{0:0}, at: process_scheduled_works+0x91b/0x1770 kernel/workqueue.c:3335
#2: ffffffff8f48b798 (unix_gc_lock){+.+.}-{2:2}, at: spin_lock include/linux/spinlock.h:351 [inline]
#2: ffffffff8f48b798 (unix_gc_lock){+.+.}-{2:2}, at: __unix_gc+0x117/0xf10 net/unix/garbage.c:261

stack backtrace:
CPU: 1 PID: 10 Comm: kworker/u8:0 Not tainted 6.8.0-syzkaller-05236-g443574b03387 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
Workqueue: events_unbound __unix_gc
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x1e7/0x2e0 lib/dump_stack.c:106
check_deadlock kernel/locking/lockdep.c:3062 [inline]
validate_chain+0x15c1/0x58e0 kernel/locking/lockdep.c:3856
__lock_acquire+0x1346/0x1fd0 kernel/locking/lockdep.c:5137
lock_acquire+0x1e4/0x530 kernel/locking/lockdep.c:5754
__raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline]
_raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:154
spin_lock include/linux/spinlock.h:351 [inline]
unix_notinflight+0x204/0x390 net/unix/garbage.c:140
unix_detach_fds net/unix/af_unix.c:1819 [inline]
unix_destruct_scm+0x221/0x350 net/unix/af_unix.c:1876
skb_release_head_state+0x100/0x250 net/core/skbuff.c:1188
skb_release_all net/core/skbuff.c:1200 [inline]
__kfree_skb net/core/skbuff.c:1216 [inline]
kfree_skb_reason+0x15d/0x390 net/core/skbuff.c:1252
kfree_skb include/linux/skbuff.h:1267 [inline]
__unix_gc+0xaf3/0xf10 net/unix/garbage.c:330
process_one_work kernel/workqueue.c:3254 [inline]
process_scheduled_works+0xa00/0x1770 kernel/workqueue.c:3335
worker_thread+0x86d/0xd70 kernel/workqueue.c:3416
kthread+0x2f0/0x390 kernel/kthread.c:388
ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:243
</TASK>


---
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[Kuniyuki Iwashima]

From: syzbot <syzbot+38b3aa...@syzkaller.appspotmail.com>
Date: Wed, 10 Apr 2024 11:45:29 -0700

#syz fix: af_unix: Clear stale u->oob_skb.

[Hillf Danton]

On Wed, 10 Apr 2024 11:45:29 -0700

> syzbot found the following issue on:
>
> HEAD commit: 443574b03387 riscv, bpf: Fix kfunc parameters incompatibil..
> git tree: bpf

> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=11aee305180000

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf.git 443574b03387

--- x/net/unix/garbage.c
+++ y/net/unix/garbage.c
@@ -327,7 +327,7 @@ static void __unix_gc(struct work_struct

#if IS_ENABLED(CONFIG_AF_UNIX_OOB)
if (u->oob_skb) {
- kfree_skb(u->oob_skb);
+ __skb_queue_tail(hitlist, u->oob_skb);
u->oob_skb = NULL;
}
#endif
--

[syzbot]

Hello,

syzbot tried to test the proposed patch but the build/boot failed:

net/unix/garbage.c:330:21: error: passing 'struct sk_buff_head' to parameter of incompatible type 'struct sk_buff_head *'; take the address with &


Tested on:

commit: 443574b0 riscv, bpf: Fix kfunc parameters incompatibil..
git tree: https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf.git

kernel config: https://syzkaller.appspot.com/x/.config?x=6fb1be60a193d440
dashboard link: https://syzkaller.appspot.com/bug?extid=38b3aa8cd529958bd27a
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40

patch: https://syzkaller.appspot.com/x/patch.diff?x=164eb66d180000