syzbot


KASAN: use-after-free Read in tty_buffer_cancel_work
Status: fixed on 2020/04/04 09:58
Reported-by: syzbot+5d29cd6e8cbe275f1c98@syzkaller.appspotmail.com
Fix commit: b9eb60a0ef39 vt: vt_ioctl: fix VT_DISALLOCATE freeing in-use virtual console
First crash: 902d, last: 814d

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 (1):
Kernel Title Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream KASAN: use-after-free Read in tty_buffer_cancel_work 4 839d 887d 0/22 closed as dup on 2020/02/24 18:35

Sample crash report:
audit: type=1400 audit(1575761028.836:36): avc:  denied  { map } for  pid=7002 comm="syz-executor322" path="/root/syz-executor322229295" dev="sda1" ino=1426 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 constant_test_bit arch/x86/include/asm/bitops.h:325 [inline]
BUG: KASAN: use-after-free in set_work_data kernel/workqueue.c:618 [inline]
BUG: KASAN: use-after-free in clear_work_data kernel/workqueue.c:681 [inline]
BUG: KASAN: use-after-free in __cancel_work_timer+0x40f/0x480 kernel/workqueue.c:2958
Read of size 8 at addr ffff888095d27388 by task syz-executor322/7012

CPU: 0 PID: 7012 Comm: syz-executor322 Not tainted 4.14.158-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+0x142/0x197 lib/dump_stack.c:58
 print_address_description.cold+0x7c/0x1dc 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+0xa9/0x2af mm/kasan/report.c:393
 __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:430
 constant_test_bit arch/x86/include/asm/bitops.h:325 [inline]
 set_work_data kernel/workqueue.c:618 [inline]
 clear_work_data kernel/workqueue.c:681 [inline]
 __cancel_work_timer+0x40f/0x480 kernel/workqueue.c:2958
 cancel_work_sync+0x18/0x20 kernel/workqueue.c:2992
 tty_buffer_cancel_work+0x16/0x20 drivers/tty/tty_buffer.c:607
 release_tty+0x3f4/0x7c0 drivers/tty/tty_io.c:1507
 tty_release_struct+0x3c/0x50 drivers/tty/tty_io.c:1616
 tty_release+0xaa3/0xd60 drivers/tty/tty_io.c:1776
 __fput+0x275/0x7a0 fs/file_table.c:210
 ____fput+0x16/0x20 fs/file_table.c:244
 task_work_run+0x114/0x190 kernel/task_work.c:113
 exit_task_work include/linux/task_work.h:22 [inline]
 do_exit+0x7be/0x2c80 kernel/exit.c:854
 do_group_exit+0x111/0x330 kernel/exit.c:951
 SYSC_exit_group kernel/exit.c:962 [inline]
 SyS_exit_group+0x1d/0x20 kernel/exit.c:960
 do_syscall_64+0x1e8/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x43ff38
RSP: 002b:00007ffe4e00bd08 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 000000000043ff38
RDX: 0000000000000000 RSI: 000000000000003c RDI: 0000000000000000
RBP: 00000000004bf950 R08: 00000000000000e7 R09: ffffffffffffffd0
R10: 0000000000000064 R11: 0000000000000246 R12: 0000000000000001
R13: 00000000006d2180 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 7012:
 save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
 save_stack+0x45/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_kmalloc mm/kasan/kasan.c:551 [inline]
 kasan_kmalloc+0xce/0xf0 mm/kasan/kasan.c:529
 kmem_cache_alloc_trace+0x152/0x790 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+0x148/0x580 drivers/tty/vt/vt.c:753
 con_install+0x52/0x400 drivers/tty/vt/vt.c:2881
 tty_driver_install_tty drivers/tty/tty_io.c:1225 [inline]
 tty_init_dev drivers/tty/tty_io.c:1338 [inline]
 tty_init_dev+0xea/0x3a0 drivers/tty/tty_io.c:1315
 tty_open_by_driver drivers/tty/tty_io.c:1973 [inline]
 tty_open+0x414/0xa10 drivers/tty/tty_io.c:2021
 chrdev_open+0x207/0x590 fs/char_dev.c:423
 do_dentry_open+0x73b/0xeb0 fs/open.c:777
 vfs_open+0x105/0x220 fs/open.c:891
 do_last fs/namei.c:3425 [inline]
 path_openat+0x8bd/0x3f70 fs/namei.c:3566
 do_filp_open+0x18e/0x250 fs/namei.c:3600
 do_sys_open+0x2c5/0x430 fs/open.c:1084
 SYSC_open fs/open.c:1102 [inline]
 SyS_open+0x2d/0x40 fs/open.c:1097
 do_syscall_64+0x1e8/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x42/0xb7

Freed by task 7017:
 save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
 save_stack+0x45/0xd0 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+0xcc/0x270 mm/slab.c:3815
 vt_disallocate_all+0x286/0x380 drivers/tty/vt/vt_ioctl.c:323
 vt_ioctl+0x76b/0x2170 drivers/tty/vt/vt_ioctl.c:816
 tty_ioctl+0x841/0x1320 drivers/tty/tty_io.c:2661
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:500 [inline]
 do_vfs_ioctl+0x7ae/0x1060 fs/ioctl.c:684
 SYSC_ioctl fs/ioctl.c:701 [inline]
 SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
 do_syscall_64+0x1e8/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x42/0xb7

The buggy address belongs to the object at ffff888095d27380
 which belongs to the cache kmalloc-2048 of size 2048
The buggy address is located 8 bytes inside of
 2048-byte region [ffff888095d27380, ffff888095d27b80)
The buggy address belongs to the page:
page:ffffea0002574980 count:1 mapcount:0 mapping:ffff888095d26280 index:0x0 compound_mapcount: 0
flags: 0xfffe0000008100(slab|head)
raw: 00fffe0000008100 ffff888095d26280 0000000000000000 0000000100000003
raw: ffffea00022aca20 ffffea0002071520 ffff8880aa800c40 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff888095d27280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888095d27300: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888095d27380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                      ^
 ffff888095d27400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888095d27480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Crashes (2):
Manager Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Title
ci2-linux-4-14 2019/12/07 23:26 linux-4.14.y a844dc4c5442 1508f453 .config log report syz C
ci2-linux-4-14 2020/01/05 06:11 linux-4.14.y 84f5ad468100 68256974 .config log report