Date:   Mon, 24 Feb 2020 10:35:30 -0800
From:   Eric Biggers <ebiggers@...nel.org>
To:     syzbot <syzbot+bd5f8de9deae03ace6a6@...kaller.appspotmail.com>
Cc:     gregkh@...uxfoundation.org, jslaby@...e.com,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: KASAN: use-after-free Read in tty_buffer_cancel_work

On Mon, Dec 23, 2019 at 09:31:08AM -0800, syzbot wrote:
> Hello,
> 
> syzbot found the following crash on:
> 
> HEAD commit:    7e0165b2 Merge branch 'akpm' (patches from Andrew)
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=154494c1e00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=1b59a3066828ac4c
> dashboard link: https://syzkaller.appspot.com/bug?extid=bd5f8de9deae03ace6a6
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> 
> Unfortunately, I don't have any reproducer for this crash yet.
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+bd5f8de9deae03ace6a6@...kaller.appspotmail.com
> 
> ==================================================================
> BUG: KASAN: use-after-free in atomic64_read
> include/asm-generic/atomic-instrumented.h:836 [inline]
> BUG: KASAN: use-after-free in atomic_long_read
> include/asm-generic/atomic-long.h:28 [inline]
> BUG: KASAN: use-after-free in work_is_canceling kernel/workqueue.c:751
> [inline]
> BUG: KASAN: use-after-free in __cancel_work_timer+0x433/0x540
> kernel/workqueue.c:3113
> Read of size 8 at addr ffff8880a77fc008 by task syz-executor.0/16211
> 
> CPU: 1 PID: 16211 Comm: syz-executor.0 Not tainted 5.5.0-rc2-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
>  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:95
>  atomic64_read include/asm-generic/atomic-instrumented.h:836 [inline]
>  atomic_long_read include/asm-generic/atomic-long.h:28 [inline]
>  work_is_canceling kernel/workqueue.c:751 [inline]
>  __cancel_work_timer+0x433/0x540 kernel/workqueue.c:3113
>  cancel_work_sync+0x18/0x20 kernel/workqueue.c:3164
>  tty_buffer_cancel_work+0x16/0x20 drivers/tty/tty_buffer.c:613
>  release_tty+0x261/0x470 drivers/tty/tty_io.c:1520
>  tty_release_struct+0x3c/0x50 drivers/tty/tty_io.c:1629
>  tty_release+0xbcb/0xe90 drivers/tty/tty_io.c:1789
>  __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
> RIP: 0033:0x4144b1
> Code: 75 14 b8 03 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 04 1b 00 00 c3 48
> 83 ec 08 e8 0a fc ff ff 48 89 04 24 b8 03 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:00007fff1f1c15d0 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
> RAX: 0000000000000000 RBX: 0000000000000004 RCX: 00000000004144b1
> RDX: 0000001b30420000 RSI: 0000000000000000 RDI: 0000000000000003
> RBP: 0000000000000001 R08: 00000000b81729f0 R09: 00000000b81729f4
> R10: 00007fff1f1c16b0 R11: 0000000000000293 R12: 000000000075bf20
> R13: 000000000005bac3 R14: 0000000000760180 R15: 000000000075bf2c
> 
> Allocated by task 16213:
>  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
>  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+0xf9/0x470 drivers/tty/tty_io.c:1318
>  tty_open_by_driver drivers/tty/tty_io.c:1987 [inline]
>  tty_open+0x4a5/0xbb0 drivers/tty/tty_io.c:2035
>  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:3420 [inline]
>  path_openat+0x10df/0x4500 fs/namei.c:3537
>  do_filp_open+0x1a1/0x280 fs/namei.c:3567
>  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 16188:
>  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
>  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:2660
>  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 ffff8880a77fc000
>  which belongs to the cache kmalloc-2k of size 2048
> The buggy address is located 8 bytes inside of
>  2048-byte region [ffff8880a77fc000, ffff8880a77fc800)
> The buggy address belongs to the page:
> page:ffffea00029dff00 refcount:1 mapcount:0 mapping:ffff8880aa400e00
> index:0x0
> raw: 00fffe0000000200 ffffea000251ef08 ffffea00029b5008 ffff8880aa400e00
> raw: 0000000000000000 ffff8880a77fc000 0000000100000001 0000000000000000
> page dumped because: kasan: bad access detected
> 

#syz dup: KASAN: use-after-free Write in release_tty

(Thread link: https://lkml.kernel.org/lkml/0000000000006663de0598d25ab1@google.com/)

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