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SubjectKASAN: use-after-free Write in release_tty
From
Hello,

syzbot found the following crash on:

HEAD commit: 596cf45c Merge branch 'akpm' (patches from Andrew)
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13dc7aeae00000
kernel config: https://syzkaller.appspot.com/x/.config?x=7d8ab2e0e09c2a82
dashboard link: https://syzkaller.appspot.com/bug?extid=522643ab5729b0421998
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=15f5d59ce00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1214042ae00000

Bisection is inconclusive: the bug happens on the oldest tested release.

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=17b01edae00000
final crash: https://syzkaller.appspot.com/x/report.txt?x=14701edae00000
console output: https://syzkaller.appspot.com/x/log.txt?x=10701edae00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+522643ab5729b0421998@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in con_shutdown+0x85/0x90
drivers/tty/vt/vt.c:3278
Write of size 8 at addr ffff88809b797108 by task syz-executor613/9470

CPU: 0 PID: 9470 Comm: syz-executor613 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
__asan_report_store8_noabort+0x17/0x20 mm/kasan/generic_report.c:140
con_shutdown+0x85/0x90 drivers/tty/vt/vt.c:3278
release_tty+0xd3/0x470 drivers/tty/tty_io.c:1511
tty_release_struct+0x3c/0x50 drivers/tty/tty_io.c:1626
tty_release+0xbcb/0xe90 drivers/tty/tty_io.c:1786
__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
exit_task_work include/linux/task_work.h:22 [inline]
do_exit+0x8e7/0x2ef0 kernel/exit.c:797
do_group_exit+0x135/0x360 kernel/exit.c:895
__do_sys_exit_group kernel/exit.c:906 [inline]
__se_sys_exit_group kernel/exit.c:904 [inline]
__x64_sys_exit_group+0x44/0x50 kernel/exit.c:904
do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x443c38
Code: 00 00 be 3c 00 00 00 eb 19 66 0f 1f 84 00 00 00 00 00 48 89 d7 89 f0
0f 05 48 3d 00 f0 ff ff 77 21 f4 48 89 d7 44 89 c0 0f 05 <48> 3d 00 f0 ff
ff 76 e0 f7 d8 64 41 89 01 eb d8 0f 1f 84 00 00 00
RSP: 002b:00007ffd7eba55f8 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 0000000000443c38
RDX: 0000000000000000 RSI: 000000000000003c RDI: 0000000000000000
RBP: 00000000004c37b0 R08: 00000000000000e7 R09: ffffffffffffffd0
R10: 000000000000000f R11: 0000000000000246 R12: 0000000000000001
R13: 00000000006d5180 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 9465:
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 9471:
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:539 [inline]
do_vfs_ioctl+0xdb6/0x13e0 fs/ioctl.c:726
ksys_ioctl+0xab/0xd0 fs/ioctl.c:743
__do_sys_ioctl fs/ioctl.c:750 [inline]
__se_sys_ioctl fs/ioctl.c:748 [inline]
__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:748
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 ffff88809b797000
which belongs to the cache kmalloc-2k of size 2048
The buggy address is located 264 bytes inside of
2048-byte region [ffff88809b797000, ffff88809b797800)
The buggy address belongs to the page:
page:ffffea00026de5c0 refcount:1 mapcount:0 mapping:ffff8880aa400e00
index:0x0
raw: 00fffe0000000200 ffffea00025c8248 ffffea00023a9a88 ffff8880aa400e00
raw: 0000000000000000 ffff88809b797000 0000000100000001 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff88809b797000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88809b797080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff88809b797100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff88809b797180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88809b797200: 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:
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

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