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SubjectKASAN: slab-out-of-bounds Write in watch_queue_ioctl
From
Hello,

syzbot found the following crash on:

HEAD commit: fca4fe89 Add linux-next specific files for 20191217
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=13447c71e00000
kernel config: https://syzkaller.appspot.com/x/.config?x=634b7ce01f79423d
dashboard link: https://syzkaller.appspot.com/bug?extid=5a774ffe70862ca9ebc7
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=13df92fee00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1003cafee00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+5a774ffe70862ca9ebc7@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-out-of-bounds in watch_queue_set_filter
drivers/misc/watch_queue.c:516 [inline]
BUG: KASAN: slab-out-of-bounds in watch_queue_ioctl+0x15ed/0x16e0
drivers/misc/watch_queue.c:555
Write of size 4 at addr ffff8880a9b31ddc by task syz-executor545/9097

CPU: 1 PID: 9097 Comm: syz-executor545 Not tainted
5.5.0-rc2-next-20191217-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+0x197/0x210 lib/dump_stack.c:118
print_address_description.constprop.0.cold+0xd4/0x30b mm/kasan/report.c:374
__kasan_report.cold+0x1b/0x41 mm/kasan/report.c:506
kasan_report+0x12/0x20 mm/kasan/common.c:639
__asan_report_store4_noabort+0x17/0x20 mm/kasan/generic_report.c:139
watch_queue_set_filter drivers/misc/watch_queue.c:516 [inline]
watch_queue_ioctl+0x15ed/0x16e0 drivers/misc/watch_queue.c:555
vfs_ioctl fs/ioctl.c:47 [inline]
file_ioctl fs/ioctl.c:545 [inline]
do_vfs_ioctl+0x977/0x14e0 fs/ioctl.c:732
ksys_ioctl+0xab/0xd0 fs/ioctl.c:749
__do_sys_ioctl fs/ioctl.c:756 [inline]
__se_sys_ioctl fs/ioctl.c:754 [inline]
__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:754
do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4401e9
Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 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 fb 13 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffe295d2878 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 00000000004401e9
RDX: 0000000020000240 RSI: 0000000000005761 RDI: 0000000000000003
RBP: 00000000006ca018 R08: 0000000000000000 R09: 00000000004002c8
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000401a70
R13: 0000000000401b00 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 9097:
save_stack+0x23/0x90 mm/kasan/common.c:72
set_track mm/kasan/common.c:80 [inline]
__kasan_kmalloc mm/kasan/common.c:513 [inline]
__kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:486
kasan_kmalloc+0x9/0x10 mm/kasan/common.c:527
__do_kmalloc mm/slab.c:3656 [inline]
__kmalloc+0x163/0x770 mm/slab.c:3665
kmalloc include/linux/slab.h:561 [inline]
kzalloc include/linux/slab.h:670 [inline]
watch_queue_set_filter drivers/misc/watch_queue.c:505 [inline]
watch_queue_ioctl+0xf57/0x16e0 drivers/misc/watch_queue.c:555
vfs_ioctl fs/ioctl.c:47 [inline]
file_ioctl fs/ioctl.c:545 [inline]
do_vfs_ioctl+0x977/0x14e0 fs/ioctl.c:732
ksys_ioctl+0xab/0xd0 fs/ioctl.c:749
__do_sys_ioctl fs/ioctl.c:756 [inline]
__se_sys_ioctl fs/ioctl.c:754 [inline]
__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:754
do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 8821:
save_stack+0x23/0x90 mm/kasan/common.c:72
set_track mm/kasan/common.c:80 [inline]
kasan_set_free_info mm/kasan/common.c:335 [inline]
__kasan_slab_free+0x102/0x150 mm/kasan/common.c:474
kasan_slab_free+0xe/0x10 mm/kasan/common.c:483
__cache_free mm/slab.c:3426 [inline]
kfree+0x10a/0x2c0 mm/slab.c:3757
single_release+0x95/0xc0 fs/seq_file.c:609
__fput+0x2ff/0x890 fs/file_table.c:280
____fput+0x16/0x20 fs/file_table.c:313
task_work_run+0x145/0x1c0 kernel/task_work.c:113
tracehook_notify_resume include/linux/tracehook.h:188 [inline]
exit_to_usermode_loop+0x316/0x380 arch/x86/entry/common.c:164
prepare_exit_to_usermode arch/x86/entry/common.c:195 [inline]
syscall_return_slowpath arch/x86/entry/common.c:278 [inline]
do_syscall_64+0x676/0x790 arch/x86/entry/common.c:304
entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8880a9b31dc0
which belongs to the cache kmalloc-32 of size 32
The buggy address is located 28 bytes inside of
32-byte region [ffff8880a9b31dc0, ffff8880a9b31de0)
The buggy address belongs to the page:
page:ffffea0002a6cc40 refcount:1 mapcount:0 mapping:ffff8880aa4001c0
index:0xffff8880a9b31fc1
raw: 00fffe0000000200 ffffea00029efd48 ffffea0002a6d4c8 ffff8880aa4001c0
raw: ffff8880a9b31fc1 ffff8880a9b31000 000000010000003b 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8880a9b31c80: 00 fc fc fc fc fc fc fc 00 fc fc fc fc fc fc fc
ffff8880a9b31d00: 00 03 fc fc fc fc fc fc 00 fc fc fc fc fc fc fc
> ffff8880a9b31d80: 00 fc fc fc fc fc fc fc 00 00 00 fc fc fc fc fc
^
ffff8880a9b31e00: 00 fc fc fc fc fc fc fc 00 fc fc fc fc fc fc fc
ffff8880a9b31e80: 00 fc fc fc fc fc fc fc 00 fc fc fc fc fc fc fc
==================================================================


---
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 syzkaller@googlegroups.com.

syzbot will keep track of this bug report. See:
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syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches

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