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SubjectKASAN: use-after-free Read in tty_open
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Hello,

syzbot found the following crash on:

HEAD commit: 76bb8b05 Merge tag 'kbuild-v5.5' of git://git.kernel.org/p..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=125c7c82e00000
kernel config: https://syzkaller.appspot.com/x/.config?x=dd226651cb0f364b
dashboard link: https://syzkaller.appspot.com/bug?extid=9af6d43c1beabec8fd05
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=16d15061e00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=14b69aeae00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+9af6d43c1beabec8fd05@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in test_bit
include/asm-generic/bitops-instrumented.h:237 [inline]
BUG: KASAN: use-after-free in tty_port_kopened include/linux/tty.h:673
[inline]
BUG: KASAN: use-after-free in tty_open_by_driver drivers/tty/tty_io.c:1964
[inline]
BUG: KASAN: use-after-free in tty_open+0x6f8/0xbb0 drivers/tty/tty_io.c:2033
Read of size 8 at addr ffff8880a2b11200 by task syz-executor362/19631

CPU: 1 PID: 19631 Comm: syz-executor362 Not tainted 5.4.0-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:638
check_memory_region_inline mm/kasan/generic.c:185 [inline]
check_memory_region+0x134/0x1a0 mm/kasan/generic.c:192
__kasan_check_read+0x11/0x20 mm/kasan/common.c:94
test_bit include/asm-generic/bitops-instrumented.h:237 [inline]
tty_port_kopened include/linux/tty.h:673 [inline]
tty_open_by_driver drivers/tty/tty_io.c:1964 [inline]
tty_open+0x6f8/0xbb0 drivers/tty/tty_io.c:2033
chrdev_open+0x245/0x6b0 fs/char_dev.c:414
do_dentry_open+0x4e6/0x1380 fs/open.c:797
vfs_open+0xa0/0xd0 fs/open.c:914
do_last fs/namei.c:3412 [inline]
path_openat+0x10e4/0x4710 fs/namei.c:3529
do_filp_open+0x1a1/0x280 fs/namei.c:3559
do_sys_open+0x3fe/0x5d0 fs/open.c:1097
__do_sys_open fs/open.c:1115 [inline]
__se_sys_open fs/open.c:1110 [inline]
__x64_sys_open+0x7e/0xc0 fs/open.c:1110
do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x405721
Code: 75 14 b8 02 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 a4 18 00 00 c3 48
83 ec 08 e8 0a fc ff ff 48 89 04 24 b8 02 00 00 00 0f 05 <48> 8b 3c 24 48
89 c2 e8 53 fc ff ff 48 89 d0 48 83 c4 08 48 3d 01
RSP: 002b:00007f4718c29980 EFLAGS: 00000293 ORIG_RAX: 0000000000000002
RAX: ffffffffffffffda RBX: 6666666666666667 RCX: 0000000000405721
RDX: 0000000000000000 RSI: 0000000000000800 RDI: 00007f4718c299a0
RBP: 00000000006dbc20 R08: 000000000000000f R09: 00007f4718c2a700
R10: 00007f4718c2a9d0 R11: 0000000000000293 R12: 00000000006dbc2c
R13: 00007ffd5b35591f R14: 00007f4718c2a9c0 R15: 000000000000002d

Allocated by task 9774:
save_stack+0x23/0x90 mm/kasan/common.c:71
set_track mm/kasan/common.c:79 [inline]
__kasan_kmalloc mm/kasan/common.c:512 [inline]
__kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:485
kasan_kmalloc+0x9/0x10 mm/kasan/common.c:526
kmem_cache_alloc_trace+0x158/0x790 mm/slab.c:3551
kmalloc include/linux/slab.h:556 [inline]
kzalloc include/linux/slab.h:670 [inline]
vc_allocate drivers/tty/vt/vt.c:1085 [inline]
vc_allocate+0x1fc/0x760 drivers/tty/vt/vt.c:1066
con_install+0x52/0x410 drivers/tty/vt/vt.c:3229
tty_driver_install_tty drivers/tty/tty_io.c:1228 [inline]
tty_init_dev drivers/tty/tty_io.c:1341 [inline]
tty_init_dev+0xf7/0x460 drivers/tty/tty_io.c:1318
tty_open_by_driver drivers/tty/tty_io.c:1985 [inline]
tty_open+0x4a5/0xbb0 drivers/tty/tty_io.c:2033
chrdev_open+0x245/0x6b0 fs/char_dev.c:414
do_dentry_open+0x4e6/0x1380 fs/open.c:797
vfs_open+0xa0/0xd0 fs/open.c:914
do_last fs/namei.c:3412 [inline]
path_openat+0x10e4/0x4710 fs/namei.c:3529
do_filp_open+0x1a1/0x280 fs/namei.c:3559
do_sys_open+0x3fe/0x5d0 fs/open.c:1097
__do_sys_open fs/open.c:1115 [inline]
__se_sys_open fs/open.c:1110 [inline]
__x64_sys_open+0x7e/0xc0 fs/open.c:1110
do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 19636:
save_stack+0x23/0x90 mm/kasan/common.c:71
set_track mm/kasan/common.c:79 [inline]
kasan_set_free_info mm/kasan/common.c:334 [inline]
__kasan_slab_free+0x102/0x150 mm/kasan/common.c:473
kasan_slab_free+0xe/0x10 mm/kasan/common.c:482
__cache_free mm/slab.c:3426 [inline]
kfree+0x10a/0x2c0 mm/slab.c:3757
vt_disallocate_all+0x2bd/0x3e0 drivers/tty/vt/vt_ioctl.c:323
vt_ioctl+0xc38/0x26d0 drivers/tty/vt/vt_ioctl.c:816
tty_ioctl+0xa37/0x14f0 drivers/tty/tty_io.c:2658
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

The buggy address belongs to the object at ffff8880a2b11000
which belongs to the cache kmalloc-2k of size 2048
The buggy address is located 512 bytes inside of
2048-byte region [ffff8880a2b11000, ffff8880a2b11800)
The buggy address belongs to the page:
page:ffffea00028ac440 refcount:1 mapcount:0 mapping:ffff8880aa400e00
index:0x0
raw: 00fffe0000000200 ffffea000288c048 ffffea0002574e48 ffff8880aa400e00
raw: 0000000000000000 ffff8880a2b11000 0000000100000001 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8880a2b11100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8880a2b11180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff8880a2b11200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff8880a2b11280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8880a2b11300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


---
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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