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From: syzbot <>
Subject: KASAN: use-after-free Write in fsnotify_detach_connector_from_object
Date: Fri, 12 Jun 2020 02:24:11 -0700	[thread overview]
Message-ID: <> (raw)


syzbot found the following crash on:

HEAD commit:    7ae77150 Merge tag 'powerpc-5.8-1' of git://
git tree:       upstream
console output:
kernel config:
dashboard link:
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:
C reproducer:

The bug was bisected to:

commit 76313c70c52f930af4afd21684509ca52297ea71
Author: Eric W. Biederman <>
Date:   Wed Feb 19 16:37:15 2020 +0000

    uml: Create a private mount of proc for mconsole

bisection log:
final crash:
console output:

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Fixes: 76313c70c52f ("uml: Create a private mount of proc for mconsole")

BUG: KASAN: use-after-free in atomic64_inc include/asm-generic/atomic-instrumented.h:1049 [inline]
BUG: KASAN: use-after-free in atomic_long_inc include/asm-generic/atomic-long.h:160 [inline]
BUG: KASAN: use-after-free in fsnotify_detach_connector_from_object+0x25e/0x380 fs/notify/mark.c:185
Write of size 8 at addr ffff88809fd7e7c0 by task syz-executor972/8021

CPU: 1 PID: 8021 Comm: syz-executor972 Not tainted 5.7.0-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+0x188/0x20d lib/dump_stack.c:118
 print_address_description.constprop.0.cold+0xd3/0x413 mm/kasan/report.c:383
 __kasan_report mm/kasan/report.c:513 [inline]
 kasan_report.cold+0x1f/0x37 mm/kasan/report.c:530
 check_memory_region_inline mm/kasan/generic.c:186 [inline]
 check_memory_region+0x141/0x190 mm/kasan/generic.c:192
 atomic64_inc include/asm-generic/atomic-instrumented.h:1049 [inline]
 atomic_long_inc include/asm-generic/atomic-long.h:160 [inline]
 fsnotify_detach_connector_from_object+0x25e/0x380 fs/notify/mark.c:185
 fsnotify_put_mark+0x367/0x580 fs/notify/mark.c:250
 fsnotify_clear_marks_by_group+0x33f/0x490 fs/notify/mark.c:764
 fsnotify_destroy_group+0xc9/0x300 fs/notify/group.c:61
 inotify_release+0x33/0x40 fs/notify/inotify/inotify_user.c:271
 __fput+0x33e/0x880 fs/file_table.c:281
 task_work_run+0xf4/0x1b0 kernel/task_work.c:123
 exit_task_work include/linux/task_work.h:22 [inline]
 do_exit+0xb3f/0x2de0 kernel/exit.c:806
 do_group_exit+0x125/0x340 kernel/exit.c:904
 __do_sys_exit_group kernel/exit.c:915 [inline]
 __se_sys_exit_group kernel/exit.c:913 [inline]
 __x64_sys_exit_group+0x3a/0x50 kernel/exit.c:913
 do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295
RIP: 0033:0x445448
Code: Bad RIP value.
RSP: 002b:00007ffe48521018 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 0000000000445448
RDX: 0000000000000000 RSI: 000000000000003c RDI: 0000000000000000
RBP: 00000000004cca90 R08: 00000000000000e7 R09: ffffffffffffffd0
R10: 00007ffe48521060 R11: 0000000000000246 R12: 0000000000000001
R13: 00000000006e0340 R14: 0000000000000007 R15: 000000000000002d

Allocated by task 8026:
 save_stack+0x1b/0x40 mm/kasan/common.c:48
 set_track mm/kasan/common.c:56 [inline]
 __kasan_kmalloc mm/kasan/common.c:494 [inline]
 __kasan_kmalloc.constprop.0+0xbf/0xd0 mm/kasan/common.c:467
 kmem_cache_alloc_trace+0x153/0x7d0 mm/slab.c:3551
 kmalloc include/linux/slab.h:555 [inline]
 kzalloc include/linux/slab.h:669 [inline]
 alloc_super+0x52/0x9d0 fs/super.c:203
 sget_fc+0x13f/0x790 fs/super.c:530
 vfs_get_super+0x6d/0x2d0 fs/super.c:1186
 vfs_get_tree+0x89/0x2f0 fs/super.c:1547
 do_new_mount fs/namespace.c:2874 [inline]
 do_mount+0x1306/0x1b40 fs/namespace.c:3199
 __do_sys_mount fs/namespace.c:3409 [inline]
 __se_sys_mount fs/namespace.c:3386 [inline]
 __x64_sys_mount+0x18f/0x230 fs/namespace.c:3386
 do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295

Freed by task 23:
 save_stack+0x1b/0x40 mm/kasan/common.c:48
 set_track mm/kasan/common.c:56 [inline]
 kasan_set_free_info mm/kasan/common.c:316 [inline]
 __kasan_slab_free+0xf7/0x140 mm/kasan/common.c:455
 __cache_free mm/slab.c:3426 [inline]
 kfree+0x109/0x2b0 mm/slab.c:3757
 process_one_work+0x965/0x16a0 kernel/workqueue.c:2268
 worker_thread+0x96/0xe20 kernel/workqueue.c:2414
 kthread+0x388/0x470 kernel/kthread.c:268
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:351

The buggy address belongs to the object at ffff88809fd7e000
 which belongs to the cache kmalloc-4k of size 4096
The buggy address is located 1984 bytes inside of
 4096-byte region [ffff88809fd7e000, ffff88809fd7f000)
The buggy address belongs to the page:
page:ffffea00027f5f80 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 head:ffffea00027f5f80 order:1 compound_mapcount:0
flags: 0xfffe0000010200(slab|head)
raw: 00fffe0000010200 ffffea000247aa88 ffffea000242ef08 ffff8880aa002000
raw: 0000000000000000 ffff88809fd7e000 0000000100000001 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff88809fd7e680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88809fd7e700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88809fd7e780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88809fd7e800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88809fd7e880: 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 for more information about syzbot.
syzbot engineers can be reached at

syzbot will keep track of this bug report. See: for how to communicate with syzbot.
For information about bisection process see:
syzbot can test patches for this bug, for details see:

             reply	other threads:[~2020-06-12  9:24 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-12  9:24 syzbot [this message]
2020-06-12 19:15 ` [PATCH] proc: Use new_inode not new_inode_pseudo Eric W. Biederman
2020-06-15  7:38   ` Jan Kara

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