KASAN: use-after-free Write in release_tty

Status: fixed on 2020/05/01 20:49
Reported-by: syzbot+699321b983dd2b7bfbcc@syzkaller.appspotmail.com
Fix commit: ca4463bf8438 vt: vt_ioctl: fix VT_DISALLOCATE freeing in-use virtual console
First crash: 2453d, last: 2334d
Fix bisection: fixed by (bisect log) :
commit b9eb60a0ef3971101c94f9cddb09708c2f900b35
Author: Eric Biggers <ebiggers@google.com>
Date: Sun Mar 22 03:43:04 2020 +0000

  vt: vt_ioctl: fix VT_DISALLOCATE freeing in-use virtual console

  
▶ ▼ Similar bugs (3)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-4.19 KASAN: use-after-free Write in release_tty 22 syz, C done 148 2337d 2454d 1/1 fixed on 2020/04/28 10:48
upstream KASAN: use-after-free Write in release_tty 22 syz, C done 591 2331d 2453d 15/29 fixed on 2020/05/10 10:41
android-6-1 KASAN: use-after-free Write in release_tty 22 1 12d 12d 0/2 premoderation: reported on 2026/08/10 10:24

Sample crash report:
audit: type=1400 audit(1585471473.165:36): avc:  denied  { map } for  pid=7442 comm="syz-executor729" path="/root/syz-executor729721826" dev="sda1" ino=16484 scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tcontext=unconfined_u:object_r:user_home_t:s0 tclass=file permissive=1
==================================================================
BUG: KASAN: use-after-free in con_shutdown+0x7f/0x90 drivers/tty/vt/vt.c:2928
Write of size 8 at addr ffff888093e03748 by task syz-executor729/7450

CPU: 1 PID: 7450 Comm: syz-executor729 Not tainted 4.14.174-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x13e/0x194 lib/dump_stack.c:58
 print_address_description.cold+0x7c/0x1e2 mm/kasan/report.c:252
 kasan_report_error mm/kasan/report.c:351 [inline]
 kasan_report mm/kasan/report.c:409 [inline]
 kasan_report.cold+0xa9/0x2ae mm/kasan/report.c:393
 con_shutdown+0x7f/0x90 drivers/tty/vt/vt.c:2928
 release_tty+0xb6/0x7a0 drivers/tty/tty_io.c:1501
 tty_release_struct+0x37/0x50 drivers/tty/tty_io.c:1616
 tty_release+0xaa6/0xd60 drivers/tty/tty_io.c:1776
 __fput+0x25f/0x790 fs/file_table.c:210
 task_work_run+0x113/0x190 kernel/task_work.c:113
 exit_task_work include/linux/task_work.h:22 [inline]
 do_exit+0x9f2/0x2b00 kernel/exit.c:858
 do_group_exit+0x100/0x310 kernel/exit.c:955
 SYSC_exit_group kernel/exit.c:966 [inline]
 SyS_exit_group+0x19/0x20 kernel/exit.c:964
 do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x43ff38
RSP: 002b:00007ffc6b69a188 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 000000000043ff38
RDX: 0000000000000000 RSI: 000000000000003c RDI: 0000000000000000
RBP: 00000000004bf950 R08: 00000000000000e7 R09: ffffffffffffffd0
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
R13: 00000000006d2180 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 7450:
 save_stack+0x32/0xa0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_kmalloc mm/kasan/kasan.c:551 [inline]
 kasan_kmalloc+0xbf/0xe0 mm/kasan/kasan.c:529
 kmem_cache_alloc_trace+0x14d/0x7b0 mm/slab.c:3618
 kmalloc include/linux/slab.h:488 [inline]
 kzalloc include/linux/slab.h:661 [inline]
 vc_allocate drivers/tty/vt/vt.c:772 [inline]
 vc_allocate+0x142/0x550 drivers/tty/vt/vt.c:753
 con_install+0x4f/0x3e0 drivers/tty/vt/vt.c:2879
 tty_driver_install_tty drivers/tty/tty_io.c:1225 [inline]
 tty_init_dev drivers/tty/tty_io.c:1338 [inline]
 tty_init_dev+0xe1/0x3a0 drivers/tty/tty_io.c:1315
 tty_open_by_driver drivers/tty/tty_io.c:1973 [inline]
 tty_open+0x410/0x9c0 drivers/tty/tty_io.c:2021
 chrdev_open+0x1fc/0x540 fs/char_dev.c:423
 do_dentry_open+0x732/0xe90 fs/open.c:777
 vfs_open+0x105/0x220 fs/open.c:888
 do_last fs/namei.c:3428 [inline]
 path_openat+0x8ca/0x3c50 fs/namei.c:3569
 do_filp_open+0x18e/0x250 fs/namei.c:3603
 do_sys_open+0x29d/0x3f0 fs/open.c:1081
 do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x42/0xb7

Freed by task 7451:
 save_stack+0x32/0xa0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_slab_free+0x75/0xc0 mm/kasan/kasan.c:524
 __cache_free mm/slab.c:3496 [inline]
 kfree+0xcb/0x260 mm/slab.c:3815
 vt_disallocate_all+0x25c/0x340 drivers/tty/vt/vt_ioctl.c:323
 vt_ioctl+0x6e3/0x1f00 drivers/tty/vt/vt_ioctl.c:816
 tty_ioctl+0x6c5/0x1220 drivers/tty/tty_io.c:2661
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:500 [inline]
 do_vfs_ioctl+0x75a/0xfe0 fs/ioctl.c:684
 SYSC_ioctl fs/ioctl.c:701 [inline]
 SyS_ioctl+0x7f/0xb0 fs/ioctl.c:692
 do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x42/0xb7

The buggy address belongs to the object at ffff888093e03640
 which belongs to the cache kmalloc-2048 of size 2048
The buggy address is located 264 bytes inside of
 2048-byte region [ffff888093e03640, ffff888093e03e40)
The buggy address belongs to the page:
page:ffffea00024f8080 count:1 mapcount:0 mapping:ffff888093e02540 index:0x0 compound_mapcount: 0
flags: 0xfffe0000008100(slab|head)
raw: 00fffe0000008100 ffff888093e02540 0000000000000000 0000000100000003
raw: ffffea00024b44a0 ffffea00024f1a20 ffff88812fe56c40 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff888093e03600: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
 ffff888093e03680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff888093e03700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                              ^
 ffff888093e03780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888093e03800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Crashes (124):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2020/03/29 08:46 linux-4.14.y 01364dad1d45 05736b29 .config console log report syz C ci2-linux-4-14
2020/03/24 08:29 linux-4.14.y 01364dad1d45 33e14df3 .config console log report syz C ci2-linux-4-14
2020/03/24 06:58 linux-4.14.y 01364dad1d45 33e14df3 .config console log report syz C ci2-linux-4-14
2020/03/22 19:08 linux-4.14.y 01364dad1d45 78267cec .config console log report syz C ci2-linux-4-14
2020/03/21 11:14 linux-4.14.y 01364dad1d45 aa6c6a55 .config console log report syz C ci2-linux-4-14
2020/03/20 21:55 linux-4.14.y 01364dad1d45 2c31c529 .config console log report syz C ci2-linux-4-14
2020/03/20 15:36 linux-4.14.y 01364dad1d45 2c31c529 .config console log report syz C ci2-linux-4-14
2020/03/18 13:55 linux-4.14.y 12cd844a39ed 0a96a13c .config console log report syz C ci2-linux-4-14
2020/03/14 23:47 linux-4.14.y 12cd844a39ed 749688d2 .config console log report syz C ci2-linux-4-14
2020/03/11 06:45 linux-4.14.y 78d697fc93f9 35f53e45 .config console log report syz C ci2-linux-4-14
2020/03/10 17:40 linux-4.14.y 78d697fc93f9 35f53e45 .config console log report syz C ci2-linux-4-14
2020/03/10 17:00 linux-4.14.y 78d697fc93f9 35f53e45 .config console log report syz C ci2-linux-4-14
2020/03/10 12:54 linux-4.14.y 78d697fc93f9 35f53e45 .config console log report syz C ci2-linux-4-14
2020/03/09 22:04 linux-4.14.y 78d697fc93f9 35f53e45 .config console log report syz C ci2-linux-4-14
2020/03/08 05:50 linux-4.14.y 78d697fc93f9 2e9971bb .config console log report syz C ci2-linux-4-14
2020/03/08 04:28 linux-4.14.y 78d697fc93f9 2e9971bb .config console log report syz C ci2-linux-4-14
2020/03/04 14:25 linux-4.14.y 78d697fc93f9 712198ac .config console log report syz C ci2-linux-4-14
2020/03/02 06:52 linux-4.14.y 78d697fc93f9 4a4e0509 .config console log report syz C ci2-linux-4-14
2020/02/29 23:38 linux-4.14.y 78d697fc93f9 c88c7b75 .config console log report syz C ci2-linux-4-14
2020/02/29 18:03 linux-4.14.y 78d697fc93f9 c88c7b75 .config console log report syz C ci2-linux-4-14
2020/02/28 20:23 linux-4.14.y 78d697fc93f9 c88c7b75 .config console log report syz C ci2-linux-4-14
2020/02/26 07:51 linux-4.14.y 98db2bf27b9e 4f588111 .config console log report syz C ci2-linux-4-14
2020/02/25 09:46 linux-4.14.y 98db2bf27b9e 59b57593 .config console log report syz C ci2-linux-4-14
2020/02/22 06:53 linux-4.14.y 98db2bf27b9e 2ffa6679 .config console log report syz C ci2-linux-4-14
2020/02/22 05:51 linux-4.14.y 98db2bf27b9e 2ffa6679 .config console log report syz C ci2-linux-4-14
2020/02/21 08:05 linux-4.14.y 98db2bf27b9e bd2a74a3 .config console log report syz C ci2-linux-4-14
2020/02/18 12:16 linux-4.14.y 98db2bf27b9e 1ce142dc .config console log report syz C ci2-linux-4-14
2020/02/17 17:52 linux-4.14.y 98db2bf27b9e 72bfa6f2 .config console log report syz C ci2-linux-4-14
2020/02/15 11:35 linux-4.14.y 98db2bf27b9e 5d7b90f1 .config console log report syz C ci2-linux-4-14
2020/02/14 16:13 linux-4.14.y e0f8b8a65a47 5d7b90f1 .config console log report syz C ci2-linux-4-14
2020/02/11 05:28 linux-4.14.y e0f8b8a65a47 d9e55b05 .config console log report syz C ci2-linux-4-14
2020/02/10 12:03 linux-4.14.y e0f8b8a65a47 35f5e45e .config console log report syz C ci2-linux-4-14
2020/02/10 01:50 linux-4.14.y e0f8b8a65a47 35f5e45e .config console log report syz C ci2-linux-4-14
2020/02/09 13:45 linux-4.14.y e0f8b8a65a47 6ece2ea5 .config console log report syz C ci2-linux-4-14
2020/02/08 05:41 linux-4.14.y e0f8b8a65a47 06150bf1 .config console log report syz C ci2-linux-4-14
2020/02/03 22:01 linux-4.14.y 9fa690a2a016 93e5e335 .config console log report syz C ci2-linux-4-14
2020/02/02 16:56 linux-4.14.y 9fa690a2a016 93e5e335 .config console log report syz C ci2-linux-4-14
2020/01/25 08:41 linux-4.14.y 8bac50406cca 2e95ab33 .config console log report syz C ci2-linux-4-14
2020/01/24 12:10 linux-4.14.y 8bac50406cca 2e95ab33 .config console log report syz C ci2-linux-4-14
2020/01/23 04:19 linux-4.14.y c1141b3aab36 3334d684 .config console log report syz C ci2-linux-4-14
2020/01/23 00:46 linux-4.14.y c1141b3aab36 3334d684 .config console log report syz C ci2-linux-4-14
2019/12/04 05:15 linux-4.14.y fbc5fe7a54d0 0ecb9746 .config console log report syz C ci2-linux-4-14
2020/04/01 11:25 linux-4.14.y 01364dad1d45 a34e2c33 .config console log report ci2-linux-4-14
2020/03/27 11:07 linux-4.14.y 01364dad1d45 9af8b4b3 .config console log report ci2-linux-4-14
2020/03/26 16:51 linux-4.14.y 01364dad1d45 6d25c5a0 .config console log report ci2-linux-4-14
2020/03/26 16:35 linux-4.14.y 01364dad1d45 6d25c5a0 .config console log report ci2-linux-4-14
2020/03/26 14:32 linux-4.14.y 01364dad1d45 6d25c5a0 .config console log report ci2-linux-4-14
2020/03/24 19:39 linux-4.14.y 01364dad1d45 68660b21 .config console log report ci2-linux-4-14
2020/03/21 18:26 linux-4.14.y 01364dad1d45 78267cec .config console log report ci2-linux-4-14
2020/03/08 14:01 linux-4.14.y 78d697fc93f9 2e9971bb .config console log report ci2-linux-4-14
2020/03/03 15:30 linux-4.14.y 78d697fc93f9 350a7a26 .config console log report ci2-linux-4-14
2020/02/26 05:13 linux-4.14.y 98db2bf27b9e 4f588111 .config console log report ci2-linux-4-14
2020/02/25 02:19 linux-4.14.y 98db2bf27b9e 59b57593 .config console log report ci2-linux-4-14
2020/02/19 05:50 linux-4.14.y 98db2bf27b9e 135c18aa .config console log report ci2-linux-4-14
2020/02/12 08:59 linux-4.14.y e0f8b8a65a47 a75b198c .config console log report ci2-linux-4-14
2020/02/10 10:45 linux-4.14.y e0f8b8a65a47 35f5e45e .config console log report ci2-linux-4-14
2020/02/06 22:07 linux-4.14.y e0f8b8a65a47 5be3a391 .config console log report ci2-linux-4-14
2020/02/06 14:27 linux-4.14.y e0f8b8a65a47 5be3a391 .config console log report ci2-linux-4-14
2020/02/02 03:00 linux-4.14.y 9fa690a2a016 2274ad39 .config console log report ci2-linux-4-14
2020/01/31 20:50 linux-4.14.y 9fa690a2a016 0eb59c27 .config console log report ci2-linux-4-14
2020/01/15 02:39 linux-4.14.y c04fc6fa5c96 fa12bd3c .config console log report ci2-linux-4-14
2020/01/13 18:21 linux-4.14.y 6d0c334a400d 99565c1a .config console log report ci2-linux-4-14
2020/01/13 00:41 linux-4.14.y 6d0c334a400d 53faa9fe .config console log report ci2-linux-4-14
2020/01/07 11:10 linux-4.14.y 84f5ad468100 1bcd407e .config console log report ci2-linux-4-14
2019/12/31 22:24 linux-4.14.y 4c5bf01e16a7 25a0186e .config console log report ci2-linux-4-14
2019/12/31 13:18 linux-4.14.y 4c5bf01e16a7 7f117e28 .config console log report ci2-linux-4-14
2019/12/28 20:47 linux-4.14.y e1f7d50ae3a3 af6b8ef8 .config console log report ci2-linux-4-14
2019/12/19 03:47 linux-4.14.y bfb9e5c03076 79b211f7 .config console log report ci2-linux-4-14
2019/12/15 00:08 linux-4.14.y a844dc4c5442 eef6e580 .config console log report ci2-linux-4-14
2019/12/09 17:47 linux-4.14.y a844dc4c5442 b31eda3d .config console log report ci2-linux-4-14
2019/12/07 21:55 linux-4.14.y a844dc4c5442 1508f453 .config console log report ci2-linux-4-14
2019/12/06 23:43 linux-4.14.y a844dc4c5442 85f26751 .config console log report ci2-linux-4-14
2019/12/06 04:41 linux-4.14.y a844dc4c5442 98b4ef2d .config console log report ci2-linux-4-14
2019/12/04 17:38 linux-4.14.y fbc5fe7a54d0 b2088328 .config console log report ci2-linux-4-14
2019/12/04 16:40 linux-4.14.y fbc5fe7a54d0 b2088328 .config console log report ci2-linux-4-14
2019/12/04 04:54 linux-4.14.y fbc5fe7a54d0 0ecb9746 .config console log report ci2-linux-4-14
* Struck through repros no longer work on HEAD.