possible deadlock in pty_flush_buffer

From: syzbot
Date: Wed Sep 16 2020 - 04:52:30 EST

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Hello,

syzbot found the following issue on:

HEAD commit: fc4f28bb Merge tag 'for-5.9-rc5-tag' of git://git.kernel.o..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11bb8555900000
kernel config: https://syzkaller.appspot.com/x/.config?x=c61f6bd349c981f3
dashboard link: https://syzkaller.appspot.com/bug?extid=42469d6bea0bd00144ad
compiler: gcc (GCC) 10.1.0-syz 20200507
userspace arch: i386

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+42469d6bea0bd00144ad@xxxxxxxxxxxxxxxxxxxxxxxxx

======================================================
WARNING: possible circular locking dependency detected
5.9.0-rc5-syzkaller #0 Not tainted
------------------------------------------------------
syz-executor.4/1625 is trying to acquire lock:
ffff88805c7f2580 (&tty->read_wait){....}-{2:2}, at: __wake_up_common_lock+0xb4/0x130 kernel/sched/wait.c:122

but task is already holding lock:
ffff8880976c93b8 (&tty->ctrl_lock){....}-{2:2}, at: spin_lock_irq include/linux/spinlock.h:379 [inline]
ffff8880976c93b8 (&tty->ctrl_lock){....}-{2:2}, at: pty_flush_buffer+0xaf/0x160 drivers/tty/pty.c:233

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #2 (&tty->ctrl_lock){....}-{2:2}:
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
_raw_spin_lock_irqsave+0x94/0xce kernel/locking/spinlock.c:159
__proc_set_tty+0x2c/0x610 drivers/tty/tty_jobctrl.c:98
proc_set_tty drivers/tty/tty_jobctrl.c:121 [inline]
tiocsctty drivers/tty/tty_jobctrl.c:384 [inline]
tty_jobctrl_ioctl+0x43c/0x1010 drivers/tty/tty_jobctrl.c:546
tty_ioctl+0x565/0x15f0 drivers/tty/tty_io.c:2651
vfs_ioctl fs/ioctl.c:48 [inline]
__do_sys_ioctl fs/ioctl.c:753 [inline]
__se_sys_ioctl fs/ioctl.c:739 [inline]
__x64_sys_ioctl+0x193/0x200 fs/ioctl.c:739
do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9

-> #1 (&sighand->siglock){-.-.}-{2:2}:
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
_raw_spin_lock_irqsave+0x94/0xce kernel/locking/spinlock.c:159
__lock_task_sighand+0x106/0x2d0 kernel/signal.c:1390
lock_task_sighand include/linux/sched/signal.h:687 [inline]
task_work_add+0x1d7/0x290 kernel/task_work.c:51
io_req_task_work_add fs/io_uring.c:1766 [inline]
__io_async_wake+0x47b/0x9f0 fs/io_uring.c:4611
__wake_up_common+0x147/0x650 kernel/sched/wait.c:93
__wake_up_common_lock+0xd0/0x130 kernel/sched/wait.c:123
tty_ldisc_lock+0x40/0xb0 drivers/tty/tty_ldisc.c:336
tty_set_ldisc+0x8e/0x670 drivers/tty/tty_ldisc.c:563
tiocsetd drivers/tty/tty_io.c:2333 [inline]
tty_ioctl+0xadf/0x15f0 drivers/tty/tty_io.c:2593
tty_compat_ioctl+0x295/0x410 drivers/tty/tty_io.c:2818
__do_compat_sys_ioctl+0x1d3/0x230 fs/ioctl.c:842
do_syscall_32_irqs_on arch/x86/entry/common.c:78 [inline]
__do_fast_syscall_32+0x60/0x90 arch/x86/entry/common.c:137
do_fast_syscall_32+0x2f/0x70 arch/x86/entry/common.c:160
entry_SYSENTER_compat_after_hwframe+0x4d/0x5c

-> #0 (&tty->read_wait){....}-{2:2}:
check_prev_add kernel/locking/lockdep.c:2496 [inline]
check_prevs_add kernel/locking/lockdep.c:2601 [inline]
validate_chain kernel/locking/lockdep.c:3218 [inline]
__lock_acquire+0x29bb/0x5570 kernel/locking/lockdep.c:4426
lock_acquire+0x1f3/0xae0 kernel/locking/lockdep.c:5006
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
_raw_spin_lock_irqsave+0x94/0xce kernel/locking/spinlock.c:159
__wake_up_common_lock+0xb4/0x130 kernel/sched/wait.c:122
pty_flush_buffer+0x124/0x160 drivers/tty/pty.c:235
tty_driver_flush_buffer drivers/tty/tty_ioctl.c:95 [inline]
__tty_perform_flush+0x13f/0x210 drivers/tty/tty_ioctl.c:871
n_tty_ioctl_helper+0x1c7/0x3a0 drivers/tty/tty_ioctl.c:937
n_tty_ioctl+0x56/0x370 drivers/tty/n_tty.c:2466
tty_ioctl+0x10c5/0x15f0 drivers/tty/tty_io.c:2665
tty_compat_ioctl+0x2d4/0x410 drivers/tty/tty_io.c:2834
__do_compat_sys_ioctl+0x1d3/0x230 fs/ioctl.c:842
do_syscall_32_irqs_on arch/x86/entry/common.c:78 [inline]
__do_fast_syscall_32+0x60/0x90 arch/x86/entry/common.c:137
do_fast_syscall_32+0x2f/0x70 arch/x86/entry/common.c:160
entry_SYSENTER_compat_after_hwframe+0x4d/0x5c

other info that might help us debug this:

Chain exists of:
&tty->read_wait --> &sighand->siglock --> &tty->ctrl_lock

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&tty->ctrl_lock);
lock(&sighand->siglock);
lock(&tty->ctrl_lock);
lock(&tty->read_wait);

*** DEADLOCK ***

2 locks held by syz-executor.4/1625:
#0: ffff8880976c9098 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x22/0x80 drivers/tty/tty_ldisc.c:267
#1: ffff8880976c93b8 (&tty->ctrl_lock){....}-{2:2}, at: spin_lock_irq include/linux/spinlock.h:379 [inline]
#1: ffff8880976c93b8 (&tty->ctrl_lock){....}-{2:2}, at: pty_flush_buffer+0xaf/0x160 drivers/tty/pty.c:233

stack backtrace:
CPU: 0 PID: 1625 Comm: syz-executor.4 Not tainted 5.9.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x198/0x1fd lib/dump_stack.c:118
check_noncircular+0x324/0x3e0 kernel/locking/lockdep.c:1827
check_prev_add kernel/locking/lockdep.c:2496 [inline]
check_prevs_add kernel/locking/lockdep.c:2601 [inline]
validate_chain kernel/locking/lockdep.c:3218 [inline]
__lock_acquire+0x29bb/0x5570 kernel/locking/lockdep.c:4426
lock_acquire+0x1f3/0xae0 kernel/locking/lockdep.c:5006
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
_raw_spin_lock_irqsave+0x94/0xce kernel/locking/spinlock.c:159
__wake_up_common_lock+0xb4/0x130 kernel/sched/wait.c:122
pty_flush_buffer+0x124/0x160 drivers/tty/pty.c:235
tty_driver_flush_buffer drivers/tty/tty_ioctl.c:95 [inline]
__tty_perform_flush+0x13f/0x210 drivers/tty/tty_ioctl.c:871
n_tty_ioctl_helper+0x1c7/0x3a0 drivers/tty/tty_ioctl.c:937
n_tty_ioctl+0x56/0x370 drivers/tty/n_tty.c:2466
tty_ioctl+0x10c5/0x15f0 drivers/tty/tty_io.c:2665
tty_compat_ioctl+0x2d4/0x410 drivers/tty/tty_io.c:2834
__do_compat_sys_ioctl+0x1d3/0x230 fs/ioctl.c:842
do_syscall_32_irqs_on arch/x86/entry/common.c:78 [inline]
__do_fast_syscall_32+0x60/0x90 arch/x86/entry/common.c:137
do_fast_syscall_32+0x2f/0x70 arch/x86/entry/common.c:160
entry_SYSENTER_compat_after_hwframe+0x4d/0x5c
RIP: 0023:0xf7f52549
Code: b8 01 10 06 03 74 b4 01 10 07 03 74 b0 01 10 08 03 74 d8 01 00 00 00 00 00 00 00 00 00 00 00 00 00 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90 90 90 90 eb 0d 90 90 90 90 90 90 90 90 90 90 90 90
RSP: 002b:00000000f554c0cc EFLAGS: 00000296 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 0000000000000004 RCX: 000000000000540b
RDX: 0000000000000002 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000

---
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Next message: Xu Wang: "[PATCH] stats: Replace seq_printf with seq_putc"
Previous message: syzbot: "KASAN: use-after-free Write in rxrpc_put_bundle"
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