KASAN: use-after-free Read in afs_deactivate_cell (2)

[syzbot <syzbot+a5e4946b04d6ca8fa5f3@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    325d0eab Merge branch 'akpm' (patches from Andrew)
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15ec729b900000
kernel config:  https://syzkaller.appspot.com/x/.config?x=8d39f8ae68f9dcd5
dashboard link: https://syzkaller.appspot.com/bug?extid=a5e4946b04d6ca8fa5f3
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+a5e4946b04d6ca8fa5f3@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in __hlist_del include/linux/list.h:826 [inline]
BUG: KASAN: use-after-free in hlist_del_rcu include/linux/rculist.h:487 [inline]
BUG: KASAN: use-after-free in afs_deactivate_cell+0x165/0x1a0 fs/afs/cell.c:647
Read of size 8 at addr ffff888090699880 by task kworker/0:3/7433

CPU: 0 PID: 7433 Comm: kworker/0:3 Not tainted 5.9.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: afs afs_manage_cell
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x198/0x1fd lib/dump_stack.c:118
 print_address_description.constprop.0.cold+0xae/0x497 mm/kasan/report.c:383
 __kasan_report mm/kasan/report.c:513 [inline]
 kasan_report.cold+0x1f/0x37 mm/kasan/report.c:530
 __hlist_del include/linux/list.h:826 [inline]
 hlist_del_rcu include/linux/rculist.h:487 [inline]
 afs_deactivate_cell+0x165/0x1a0 fs/afs/cell.c:647
 afs_manage_cell+0x326/0x11c0 fs/afs/cell.c:721
 process_one_work+0x94c/0x1670 kernel/workqueue.c:2269
 process_scheduled_works kernel/workqueue.c:2331 [inline]
 worker_thread+0x82b/0x1120 kernel/workqueue.c:2417
 kthread+0x3b5/0x4a0 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

Allocated by task 19085:
 kasan_save_stack+0x1b/0x40 mm/kasan/common.c:48
 kasan_set_track mm/kasan/common.c:56 [inline]
 __kasan_kmalloc.constprop.0+0xbf/0xd0 mm/kasan/common.c:461
 kmem_cache_alloc_trace+0x174/0x300 mm/slab.c:3550
 kmalloc include/linux/slab.h:554 [inline]
 kzalloc include/linux/slab.h:666 [inline]
 afs_alloc_cell fs/afs/cell.c:151 [inline]
 afs_lookup_cell+0x5c8/0x1440 fs/afs/cell.c:262
 afs_parse_source fs/afs/super.c:290 [inline]
 afs_parse_param+0x404/0x8c0 fs/afs/super.c:326
 vfs_parse_fs_param fs/fs_context.c:117 [inline]
 vfs_parse_fs_param+0x203/0x550 fs/fs_context.c:98
 vfs_parse_fs_string+0xe6/0x150 fs/fs_context.c:161
 generic_parse_monolithic+0x16f/0x1f0 fs/fs_context.c:201
 do_new_mount fs/namespace.c:2871 [inline]
 path_mount+0x133f/0x20a0 fs/namespace.c:3192
 do_mount fs/namespace.c:3205 [inline]
 __do_sys_mount fs/namespace.c:3413 [inline]
 __se_sys_mount fs/namespace.c:3390 [inline]
 __x64_sys_mount+0x27f/0x300 fs/namespace.c:3390
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Freed by task 9:
 kasan_save_stack+0x1b/0x40 mm/kasan/common.c:48
 kasan_set_track+0x1c/0x30 mm/kasan/common.c:56
 kasan_set_free_info+0x1b/0x30 mm/kasan/generic.c:355
 __kasan_slab_free+0xd8/0x120 mm/kasan/common.c:422
 __cache_free mm/slab.c:3418 [inline]
 kfree+0x10e/0x2b0 mm/slab.c:3756
 rcu_do_batch kernel/rcu/tree.c:2428 [inline]
 rcu_core+0x5ca/0x1130 kernel/rcu/tree.c:2656
 __do_softirq+0x1f8/0xb23 kernel/softirq.c:298

Last call_rcu():
 kasan_save_stack+0x1b/0x40 mm/kasan/common.c:48
 kasan_record_aux_stack+0x82/0xb0 mm/kasan/generic.c:346
 __call_rcu kernel/rcu/tree.c:2894 [inline]
 call_rcu+0x15e/0x7c0 kernel/rcu/tree.c:2968
 afs_manage_cell+0x250/0x11c0 fs/afs/cell.c:751
 process_one_work+0x94c/0x1670 kernel/workqueue.c:2269
 worker_thread+0x64c/0x1120 kernel/workqueue.c:2415
 kthread+0x3b5/0x4a0 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

The buggy address belongs to the object at ffff888090699800
 which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 128 bytes inside of
 1024-byte region [ffff888090699800, ffff888090699c00)
The buggy address belongs to the page:
page:00000000d3e3a7d0 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x90699
flags: 0xfffe0000000200(slab)
raw: 00fffe0000000200 ffffea0002558fc8 ffffea0001240988 ffff8880aa040700
raw: 0000000000000000 ffff888090699000 0000000100000002 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff888090699780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888090699800: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff888090699880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                   ^
 ffff888090699900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888090699980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


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