KASAN: null-ptr-deref Write in queue_work_on

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 6e625a1a Merge tag 'xtensa-20190816' of git://github.com/j..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=174e04ac600000
kernel config: https://syzkaller.appspot.com/x/.config?x=3ff364e429585cf2
dashboard link: https://syzkaller.appspot.com/bug?extid=017e491ae13c0068598a
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1327d9e2600000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16c4fc4c600000

Bisection is inconclusive: the first bad commit could be any of:

569dbb88 Linux 4.13
that is not the commit

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=17520702600000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+017e49...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: null-ptr-deref in test_and_set_bit
include/asm-generic/bitops-instrumented.h:143 [inline]
BUG: KASAN: null-ptr-deref in queue_work_on+0xa6/0x210
kernel/workqueue.c:1517
Write of size 8 at addr 0000000000000050 by task syz-executor935/9691

CPU: 0 PID: 9691 Comm: syz-executor935 Not tainted 5.3.0-rc4+ #113
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+0x172/0x1f0 lib/dump_stack.c:113
__kasan_report.cold+0x5/0x36 mm/kasan/report.c:486
kasan_report+0x12/0x17 mm/kasan/common.c:612
check_memory_region_inline mm/kasan/generic.c:185 [inline]
check_memory_region+0x134/0x1a0 mm/kasan/generic.c:192
__kasan_check_write+0x14/0x20 mm/kasan/common.c:98
test_and_set_bit include/asm-generic/bitops-instrumented.h:143 [inline]
queue_work_on+0xa6/0x210 kernel/workqueue.c:1517
queue_work include/linux/workqueue.h:490 [inline]
schedule_work include/linux/workqueue.h:548 [inline]
slcan_write_wakeup+0x66/0x90 drivers/net/can/slcan.c:348
tty_wakeup+0xe9/0x120 drivers/tty/tty_io.c:535
pty_unthrottle+0x37/0x60 drivers/tty/pty.c:95
tty_unthrottle+0xab/0x110 drivers/tty/tty_ioctl.c:139
__tty_perform_flush+0x1b3/0x200 drivers/tty/tty_ioctl.c:861
n_tty_ioctl_helper+0x1cc/0x3b0 drivers/tty/tty_ioctl.c:937
n_tty_ioctl+0x59/0x370 drivers/tty/n_tty.c:2466
tty_ioctl+0xaf9/0x14f0 drivers/tty/tty_io.c:2666
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:509 [inline]
do_vfs_ioctl+0xdb6/0x13e0 fs/ioctl.c:696
ksys_ioctl+0xab/0xd0 fs/ioctl.c:713
__do_sys_ioctl fs/ioctl.c:720 [inline]
__se_sys_ioctl fs/ioctl.c:718 [inline]
__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
do_syscall_64+0xfd/0x6a0 arch/x86/entry/common.c:296
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x446859
Code: e8 9c b4 02 00 48 83 c4 18 c3 0f 1f 80 00 00 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 0f 83 eb 07 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f17a0a3fd18 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000006dbc38 RCX: 0000000000446859
RDX: 0000000000000000 RSI: 000000000000540b RDI: 0000000000000003
RBP: 00000000006dbc30 R08: 00007f17a0a40700 R09: 0000000000000000
R10: 00007f17a0a40700 R11: 0000000000000246 R12: 00000000006dbc3c
R13: 00007ffdfd0bdb5f R14: 00007f17a0a409c0 R15: 20c49ba5e353f7cf
==================================================================


---
This bug 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 syzk...@googlegroups.com.

syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
For information about bisection process see: https://goo.gl/tpsmEJ#bisection
syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches

[Hillf Danton]

On Wed, 21 Aug 2019 15:38:08 -0700 (PDT)

Add mb.

--- a/drivers/net/can/slcan.c
+++ b/drivers/net/can/slcan.c
@@ -345,7 +345,9 @@ static void slcan_write_wakeup(struct tt
{
struct slcan *sl = tty->disc_data;

- schedule_work(&sl->tx_work);
+ smp_rmb(); /* help see writer's updates */
+ if (sl)
+ schedule_work(&sl->tx_work);
}

/* Send a can_frame to a TTY queue. */
@@ -637,6 +639,7 @@ static void slcan_close(struct tty_struc
if (!sl || sl->magic != SLCAN_MAGIC || sl->tty != tty)
return;

+ smp_wmb(); /* Let reader know updates here */
spin_lock_bh(&sl->lock);
tty->disc_data = NULL;
sl->tty = NULL;
--