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[parent not found: <20260903034152.122978-1-adrianox@gmail.com>]
[parent not found: <20260903032431.120530-1-adrianox@gmail.com>]
* [PATCH] tty: fix break race
@ 2026-09-03  2:24 Adriano Cordova
  2026-09-03  2:41 ` [syzbot] [usb?] general protection fault in keyspan_break_ctl syzbot
  0 siblings, 1 reply; 7+ messages in thread
From: Adriano Cordova @ 2026-09-03  2:24 UTC (permalink / raw)
  To: adrianox; +Cc: Johan Hovold, syzbot+473d7477c523b41d4046, stable

A timed break (TCSBRK and TCSBRKP) can race against hangup and end up
calling into a tty driver after the underlying device has been removed,
for example when a USB serial device is disconnected while a break is in
progress. This can result in a use-after-free or NULL-pointer dereference
in the driver when the second break_ctl() call is made after the sleep,
as reported for the keyspan USB serial driver.

Make send_break() wait only for the break duration and then check the
hung-up state of the tty before invoking the driver a second time. Since
the tty is marked hung up (f_op == &hung_up_tty_fops) before the device is
torn down, the second break_ctl() is no longer issued after a hangup and
the driver is not called for a device that is gone.

Suggested-by: Johan Hovold <johan@kernel.org>
Reported-by: syzbot+473d7477c523b41d4046@syzkaller.appspotmail.com
Link: https://syzkaller.appspot.com/bug?extid=473d7477c523b41d4046
Assisted-by: opencode:deepseek-v4-flash
Cc: stable@vger.kernel.org
Signed-off-by: Adriano Cordova <adrianox@gmail.com>
#syz test
---
 drivers/tty/tty_io.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 48569035da56..c9d8a138b84c 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -2429,6 +2429,7 @@ static int tiocgetd(struct tty_struct *tty, int __user *p)
 
 /**
  * send_break - performed time break
+ * @file: file object
  * @tty: device to break on
  * @duration: timeout in mS
  *
@@ -2438,7 +2439,7 @@ static int tiocgetd(struct tty_struct *tty, int __user *p)
  * Locking:
  *	@tty->atomic_write_lock serializes
  */
-static int send_break(struct tty_struct *tty, unsigned int duration)
+static int send_break(struct file *file, struct tty_struct *tty, unsigned int duration)
 {
 	int retval;
 
@@ -2455,7 +2456,10 @@ static int send_break(struct tty_struct *tty, unsigned int duration)
 	retval = tty->ops->break_ctl(tty, -1);
 	if (!retval) {
 		msleep_interruptible(duration);
-		retval = tty->ops->break_ctl(tty, 0);
+		if (tty_hung_up_p(file))
+			retval = -EIO;
+		else
+			retval = tty->ops->break_ctl(tty, 0);
 	} else if (retval == -EOPNOTSUPP) {
 		/* some drivers can tell only dynamically */
 		retval = 0;
@@ -2727,10 +2731,10 @@ long tty_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 		 * This is used by the tcdrain() termios function.
 		 */
 		if (!arg)
-			return send_break(tty, 250);
+			return send_break(file, tty, 250);
 		return 0;
 	case TCSBRKP:	/* support for POSIX tcsendbreak() */
-		return send_break(tty, arg ? arg*100 : 250);
+		return send_break(file, tty, arg ? arg * 100 : 250);
 
 	case TIOCMGET:
 		return tty_tiocmget(tty, p);
-- 
2.51.0


^ permalink raw reply related	[flat|nested] 7+ messages in thread
* [syzbot] [usb?] general protection fault in keyspan_break_ctl
@ 2026-08-27 18:53 syzbot
  2026-08-28  6:53 ` Johan Hovold
  2026-09-03 14:55 ` syzbot
  0 siblings, 2 replies; 7+ messages in thread
From: syzbot @ 2026-08-27 18:53 UTC (permalink / raw)
  To: gregkh, johan, linux-kernel, linux-usb, syzkaller-bugs

Hello,

syzbot found the following issue on:

HEAD commit:    818bebeb63dd drm/xe: Don't hand out the flat CCS storage a..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16ba2979580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=ccca94d2c01b9e78
dashboard link: https://syzkaller.appspot.com/bug?extid=473d7477c523b41d4046
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=161f499e580000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-818bebeb.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/6e4100526b12/vmlinux-818bebeb.xz
kernel image: https://storage.googleapis.com/syzbot-assets/723c4783ee96/bzImage-818bebeb.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+473d7477c523b41d4046@syzkaller.appspotmail.com

Oops: general protection fault, probably for non-canonical address 0xdffffc0000000013: 0000 [#1] SMP KASAN NOPTI
KASAN: null-ptr-deref in range [0x0000000000000098-0x000000000000009f]
CPU: 2 UID: 0 PID: 6029 Comm: syz.3.20 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
RIP: 0010:keyspan_break_ctl+0x8e/0xe0 drivers/usb/serial/keyspan.c:608
Code: ff ff ff e8 54 ca 48 fa 83 fb ff 48 b8 00 00 00 00 00 fc ff df 49 8d bc 24 9c 00 00 00 0f 94 c3 48 89 fa 0f b6 db 48 c1 ea 03 <0f> b6 14 02 48 89 f8 83 e0 07 83 c0 03 38 d0 7c 04 84 d2 75 1d 41
RSP: 0018:ffffc900035b7cb0 EFLAGS: 00010203
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: ffffffff87c231ec
RDX: 0000000000000013 RSI: 00000000ffffffff RDI: 000000000000009c
RBP: ffff88802f436000 R08: 0000000000000005 R09: 00000000ffffffff
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: ffff888034d39020 R14: ffff888034d390c8 R15: 0000000000000000
FS:  0000555589f16500(0000) GS:ffff8880d5da2000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f5bac070000 CR3: 00000000584fe000 CR4: 0000000000352ef0
Call Trace:
 <TASK>
 serial_break+0xcb/0x160 drivers/usb/serial/usb-serial.c:538
 send_break drivers/tty/tty_io.c:2458 [inline]
 send_break+0x2ec/0x370 drivers/tty/tty_io.c:2441
 tty_ioctl+0xa2c/0x1640 drivers/tty/tty_io.c:2733
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl fs/ioctl.c:583 [inline]
 __x64_sys_ioctl+0x18e/0x210 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f5bac19e0d9
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffd93db7608 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f5bac425fa0 RCX: 00007f5bac19e0d9
RDX: 0000000000000000 RSI: 0000000000005425 RDI: 0000000000000004
RBP: 00007f5bac235024 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f5bac425fac R14: 00007f5bac425fa0 R15: 00007f5bac425fa0
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:keyspan_break_ctl+0x8e/0xe0 drivers/usb/serial/keyspan.c:608
Code: ff ff ff e8 54 ca 48 fa 83 fb ff 48 b8 00 00 00 00 00 fc ff df 49 8d bc 24 9c 00 00 00 0f 94 c3 48 89 fa 0f b6 db 48 c1 ea 03 <0f> b6 14 02 48 89 f8 83 e0 07 83 c0 03 38 d0 7c 04 84 d2 75 1d 41
RSP: 0018:ffffc900035b7cb0 EFLAGS: 00010203
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: ffffffff87c231ec
RDX: 0000000000000013 RSI: 00000000ffffffff RDI: 000000000000009c
RBP: ffff88802f436000 R08: 0000000000000005 R09: 00000000ffffffff
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: ffff888034d39020 R14: ffff888034d390c8 R15: 0000000000000000
FS:  0000555589f16500(0000) GS:ffff8880d5da2000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f5bac070000 CR3: 00000000584fe000 CR4: 0000000000352ef0
----------------
Code disassembly (best guess), 2 bytes skipped:
   0:	ff                   	ljmp   (bad)
   1:	e8 54 ca 48 fa       	call   0xfa48ca5a
   6:	83 fb ff             	cmp    $0xffffffff,%ebx
   9:	48 b8 00 00 00 00 00 	movabs $0xdffffc0000000000,%rax
  10:	fc ff df
  13:	49 8d bc 24 9c 00 00 	lea    0x9c(%r12),%rdi
  1a:	00
  1b:	0f 94 c3             	sete   %bl
  1e:	48 89 fa             	mov    %rdi,%rdx
  21:	0f b6 db             	movzbl %bl,%ebx
  24:	48 c1 ea 03          	shr    $0x3,%rdx
* 28:	0f b6 14 02          	movzbl (%rdx,%rax,1),%edx <-- trapping instruction
  2c:	48 89 f8             	mov    %rdi,%rax
  2f:	83 e0 07             	and    $0x7,%eax
  32:	83 c0 03             	add    $0x3,%eax
  35:	38 d0                	cmp    %dl,%al
  37:	7c 04                	jl     0x3d
  39:	84 d2                	test   %dl,%dl
  3b:	75 1d                	jne    0x5a
  3d:	41                   	rex.B


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this issue. See:
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If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

If you want to overwrite report's subsystems, reply with:
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(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup

^ permalink raw reply	[flat|nested] 7+ messages in thread
end of thread, other threads:[~2026-09-03 14:55 UTC | newest]

Thread overview: 7+ messages (download: mbox.gz follow: Atom feed
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     [not found] <20260828012840.12003-1-kartikey406@gmail.com>
2026-08-28  1:52 ` [syzbot] [usb?] general protection fault in keyspan_break_ctl syzbot
     [not found] <20260903034152.122978-1-adrianox@gmail.com>
2026-09-03  4:03 ` syzbot
     [not found] <20260903032431.120530-1-adrianox@gmail.com>
2026-09-03  3:40 ` syzbot
2026-09-03  2:24 [PATCH] tty: fix break race Adriano Cordova
2026-09-03  2:41 ` [syzbot] [usb?] general protection fault in keyspan_break_ctl syzbot
  -- strict thread matches above, loose matches on Subject: below --
2026-08-27 18:53 syzbot
2026-08-28  6:53 ` Johan Hovold
2026-09-03 14:55 ` syzbot

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