Re: [syzbot] [kernel?] KASAN: slab-use-after-free Read in __unix_gc

[syzbot <syzbot+5a630f8ca0120ab43f55@syzkaller.appspotmail.com>]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
INFO: task hung in unix_stream_sendmsg

INFO: task syz-executor.0:7136 blocked for more than 143 seconds.
      Not tainted 6.8.0-rc3-syzkaller-00811-gb63cc73341e0-dirty #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz-executor.0  state:D stack:25200 pid:7136  tgid:7135  ppid:5423   flags:0x00004006
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5400 [inline]
 __schedule+0x17d1/0x49f0 kernel/sched/core.c:6727
 __schedule_loop kernel/sched/core.c:6802 [inline]
 schedule+0x149/0x260 kernel/sched/core.c:6817
 schedule_timeout+0xb0/0x310 kernel/time/timer.c:2159
 do_wait_for_common kernel/sched/completion.c:95 [inline]
 __wait_for_common kernel/sched/completion.c:116 [inline]
 wait_for_common kernel/sched/completion.c:127 [inline]
 wait_for_completion+0x354/0x620 kernel/sched/completion.c:148
 __flush_work+0x950/0xad0 kernel/workqueue.c:3410
 unix_stream_sendmsg+0x1c3/0xe60 net/unix/af_unix.c:2264
 sock_sendmsg_nosec net/socket.c:730 [inline]
 __sock_sendmsg+0x221/0x270 net/socket.c:745
 ____sys_sendmsg+0x525/0x7d0 net/socket.c:2584
 ___sys_sendmsg net/socket.c:2638 [inline]
 __sys_sendmsg+0x2b0/0x3a0 net/socket.c:2667
 do_syscall_64+0xf9/0x240
 entry_SYSCALL_64_after_hwframe+0x6f/0x77
RIP: 0033:0x7f5b08e7dda9
RSP: 002b:00007f5b09cb70c8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007f5b08fabf80 RCX: 00007f5b08e7dda9
RDX: 0000000020004005 RSI: 0000000020000280 RDI: 0000000000000004
RBP: 00007f5b08eca47a R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 000000000000000b R14: 00007f5b08fabf80 R15: 00007fffbd0155e8
 </TASK>

Showing all locks held in the system:
1 lock held by khungtaskd/29:
 #0: ffffffff8e130ae0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:298 [inline]
 #0: ffffffff8e130ae0 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:750 [inline]
 #0: ffffffff8e130ae0 (rcu_read_lock){....}-{1:2}, at: debug_show_all_locks+0x55/0x2a0 kernel/locking/lockdep.c:6614
2 locks held by kworker/u4:7/2789:
2 locks held by getty/4819:
 #0: ffff88802a9d20a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:243
 #1: ffffc90002efe2f0 (&ldata->atomic_read_lock){+.+.}-{3:3}, at: n_tty_read+0x6b4/0x1e10 drivers/tty/n_tty.c:2201

=============================================

NMI backtrace for cpu 1
CPU: 1 PID: 29 Comm: khungtaskd Not tainted 6.8.0-rc3-syzkaller-00811-gb63cc73341e0-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/25/2024
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x1e7/0x2e0 lib/dump_stack.c:106
 nmi_cpu_backtrace+0x49c/0x4d0 lib/nmi_backtrace.c:113
 nmi_trigger_cpumask_backtrace+0x198/0x320 lib/nmi_backtrace.c:62
 trigger_all_cpu_backtrace include/linux/nmi.h:160 [inline]
 check_hung_uninterruptible_tasks kernel/hung_task.c:222 [inline]
 watchdog+0xfaf/0xff0 kernel/hung_task.c:379
 kthread+0x2ef/0x390 kernel/kthread.c:388
 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1b/0x30 arch/x86/entry/entry_64.S:242
 </TASK>
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 132 Comm: kworker/u4:5 Not tainted 6.8.0-rc3-syzkaller-00811-gb63cc73341e0-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/25/2024
Workqueue: bat_events batadv_nc_worker
RIP: 0010:lockdep_hardirqs_on+0x71/0x140 kernel/locking/lockdep.c:4409
Code: c0 75 74 65 8b 05 c7 28 9b 74 85 c0 75 69 83 3d 04 35 e1 08 00 75 2e 48 c7 04 24 00 00 00 00 9c 8f 04 24 f7 04 24 00 02 00 00 <75> 67 83 3d e6 34 e1 08 00 75 10 48 8b 83 98 0a 00 00 48 3b 83 b0
RSP: 0018:ffffc90002d57a18 EFLAGS: 00000046
RAX: 0000000000000000 RBX: ffff88801cf7bb80 RCX: ffffffff8171840a
RDX: dffffc0000000000 RSI: ffffffff8baac760 RDI: ffffffff81592108
RBP: ffffc90002d57af0 R08: ffffffff92c914f7 R09: 1ffffffff259229e
R10: dffffc0000000000 R11: fffffbfff259229f R12: dffffc0000000000
R13: 1ffff920005aaf50 R14: ffffffff81592108 R15: 0000000000000201
FS:  0000000000000000(0000) GS:ffff8880b9400000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f210bda80c0 CR3: 000000000df32000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <NMI>
 </NMI>
 <TASK>
 __local_bh_enable_ip+0x168/0x200 kernel/softirq.c:386
 spin_unlock_bh include/linux/spinlock.h:396 [inline]
 batadv_nc_purge_paths+0x30f/0x3b0 net/batman-adv/network-coding.c:471
 batadv_nc_worker+0x328/0x610 net/batman-adv/network-coding.c:720
 process_one_work kernel/workqueue.c:2633 [inline]
 process_scheduled_works+0x913/0x1420 kernel/workqueue.c:2706
 worker_thread+0xa5f/0x1000 kernel/workqueue.c:2787
 kthread+0x2ef/0x390 kernel/kthread.c:388
 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1b/0x30 arch/x86/entry/entry_64.S:242
 </TASK>


Tested on:

commit:         b63cc733 net: phy: realtek: use generic MDIO helpers t..
git tree:       https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git main
console output: https://syzkaller.appspot.com/x/log.txt?x=16d4bd20180000
kernel config:  https://syzkaller.appspot.com/x/.config?x=ac1116e4986e7570
dashboard link: https://syzkaller.appspot.com/bug?extid=5a630f8ca0120ab43f55
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=15e9e3a2180000