KASAN: use-after-free Read in ceph_mdsc_destroy

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: f932d58a Merge tag 'scsi-fixes' of git://git.kernel.org/pu..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=152c6a80900000
kernel config: https://syzkaller.appspot.com/x/.config?x=a160d1053fc89af5
dashboard link: https://syzkaller.appspot.com/bug?extid=b57f46d8d6ea51960b8c
compiler: gcc (GCC) 10.1.0-syz 20200507

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b57f46...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in timer_is_static_object+0x7a/0x90 kernel/time/timer.c:611
Read of size 8 at addr ffff88809e482380 by task syz-executor.3/15653

CPU: 0 PID: 15653 Comm: syz-executor.3 Not tainted 5.8.0-rc5-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+0x18f/0x20d lib/dump_stack.c:118
print_address_description.constprop.0.cold+0xae/0x436 mm/kasan/report.c:383
__kasan_report mm/kasan/report.c:513 [inline]
kasan_report.cold+0x1f/0x37 mm/kasan/report.c:530
timer_is_static_object+0x7a/0x90 kernel/time/timer.c:611
debug_object_assert_init lib/debugobjects.c:866 [inline]
debug_object_assert_init+0x1df/0x2e0 lib/debugobjects.c:841
debug_timer_assert_init kernel/time/timer.c:728 [inline]
debug_assert_init kernel/time/timer.c:773 [inline]
del_timer+0x6d/0x110 kernel/time/timer.c:1196
try_to_grab_pending kernel/workqueue.c:1249 [inline]
__cancel_work_timer+0x12d/0x700 kernel/workqueue.c:3092
ceph_mdsc_stop fs/ceph/mds_client.c:4660 [inline]
ceph_mdsc_destroy+0x50/0x140 fs/ceph/mds_client.c:4679
destroy_fs_client+0x13/0x200 fs/ceph/super.c:720
ceph_get_tree+0x9e5/0x1660 fs/ceph/super.c:1110
vfs_get_tree+0x89/0x2f0 fs/super.c:1547
do_new_mount fs/namespace.c:2875 [inline]
do_mount+0x1592/0x1fe0 fs/namespace.c:3200
__do_sys_mount fs/namespace.c:3410 [inline]
__se_sys_mount fs/namespace.c:3387 [inline]
__x64_sys_mount+0x18f/0x230 fs/namespace.c:3387
do_syscall_64+0x60/0xe0 arch/x86/entry/common.c:384
entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x45c1d9
Code: Bad RIP value.
RSP: 002b:00007f33d2bc0c78 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 000000000001f400 RCX: 000000000045c1d9
RDX: 0000000020000140 RSI: 00000000200000c0 RDI: 00000000200005c0
RBP: 000000000078bf50 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000078bf0c
R13: 00007fffaad3cc8f R14: 00007f33d2bc19c0 R15: 000000000078bf0c

Allocated by task 15653:
save_stack+0x1b/0x40 mm/kasan/common.c:48
set_track mm/kasan/common.c:56 [inline]
__kasan_kmalloc.constprop.0+0xc2/0xd0 mm/kasan/common.c:494
kmem_cache_alloc_trace+0x14f/0x2d0 mm/slab.c:3551
kmalloc include/linux/slab.h:555 [inline]
kzalloc include/linux/slab.h:669 [inline]
ceph_mdsc_init+0x47/0xf10 fs/ceph/mds_client.c:4351
ceph_get_tree+0x4fe/0x1660 fs/ceph/super.c:1063
vfs_get_tree+0x89/0x2f0 fs/super.c:1547
do_new_mount fs/namespace.c:2875 [inline]
do_mount+0x1592/0x1fe0 fs/namespace.c:3200
__do_sys_mount fs/namespace.c:3410 [inline]
__se_sys_mount fs/namespace.c:3387 [inline]
__x64_sys_mount+0x18f/0x230 fs/namespace.c:3387
do_syscall_64+0x60/0xe0 arch/x86/entry/common.c:384
entry_SYSCALL_64_after_hwframe+0x44/0xa9

Freed by task 15653:
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+0xf5/0x140 mm/kasan/common.c:455
__cache_free mm/slab.c:3426 [inline]
kfree+0x103/0x2c0 mm/slab.c:3757
ceph_mdsc_init+0xc64/0xf10 fs/ceph/mds_client.c:4422
ceph_get_tree+0x4fe/0x1660 fs/ceph/super.c:1063
vfs_get_tree+0x89/0x2f0 fs/super.c:1547
do_new_mount fs/namespace.c:2875 [inline]
do_mount+0x1592/0x1fe0 fs/namespace.c:3200
__do_sys_mount fs/namespace.c:3410 [inline]
__se_sys_mount fs/namespace.c:3387 [inline]
__x64_sys_mount+0x18f/0x230 fs/namespace.c:3387
do_syscall_64+0x60/0xe0 arch/x86/entry/common.c:384
entry_SYSCALL_64_after_hwframe+0x44/0xa9

The buggy address belongs to the object at ffff88809e482000
which belongs to the cache kmalloc-4k of size 4096
The buggy address is located 896 bytes inside of
4096-byte region [ffff88809e482000, ffff88809e483000)
The buggy address belongs to the page:
page:ffffea0002792080 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 head:ffffea0002792080 order:1 compound_mapcount:0
flags: 0xfffe0000010200(slab|head)
raw: 00fffe0000010200 ffffea0002792008 ffffea000241dc08 ffff8880aa002000
raw: 0000000000000000 ffff88809e482000 0000000100000001 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff88809e482280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88809e482300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88809e482380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff88809e482400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88809e482480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


---
This report 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 syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

[Xiubo Li]

On 2020/7/23 14:27, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: f932d58a Merge tag 'scsi-fixes' of git://git.kernel.org/pu..
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=152c6a80900000
> kernel config: https://syzkaller.appspot.com/x/.config?x=a160d1053fc89af5
> dashboard link: https://syzkaller.appspot.com/bug?extid=b57f46d8d6ea51960b8c
> compiler: gcc (GCC) 10.1.0-syz 20200507
>
> Unfortunately, I don't have any reproducer for this issue yet.
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+b57f46...@syzkaller.appspotmail.com
>
> ==================================================================
> BUG: KASAN: use-after-free in timer_is_static_object+0x7a/0x90 kernel/time/timer.c:611
> Read of size 8 at addr ffff88809e482380 by task syz-executor.3/15653

If the ceph_mdsc_init() fails, it will free the mdsc already. After
freed we should set it to NULL.

I will fix it.

Thanks for reporting.