Re: [syzbot] [net?] possible deadlock in unix_notinflight

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From: syzbot <syzbot+38b3aa8cd529958bd27a@syzkaller.appspotmail.com>
Date: Wed, 10 Apr 2024 11:45:29 -0700
> 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+38b3aa8cd529958bd27a@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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> 
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> If the report is already addressed, let syzbot know by replying with:
> #syz fix: exact-commit-title

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