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BUG: KASAN: use-after-free in mntput+0x91/0xa0 fs/namespace.c:1207
Read of size 4 at addr ffff88809f99e924 by task syz-executor113/10231

CPU: 1 PID: 10231 Comm: syz-executor113 Not tainted 5.2.0-rc4 #44
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+0x172/0x1f0 lib/dump_stack.c:113
 print_address_description.cold+0x7c/0x20d mm/kasan/report.c:188
 __kasan_report.cold+0x1b/0x40 mm/kasan/report.c:317
 kasan_report+0x12/0x20 mm/kasan/common.c:614
 __asan_report_load4_noabort+0x14/0x20 mm/kasan/generic_report.c:131
 mntput+0x91/0xa0 fs/namespace.c:1207
 path_put+0x50/0x70 fs/namei.c:483
 free_fs_struct+0x25/0x70 fs/fs_struct.c:91
 exit_fs+0xf0/0x130 fs/fs_struct.c:108
 do_exit+0x8e0/0x2fa0 kernel/exit.c:873
 do_group_exit+0x135/0x370 kernel/exit.c:981
 __do_sys_exit_group kernel/exit.c:992 [inline]
 __se_sys_exit_group kernel/exit.c:990 [inline]
 __x64_sys_exit_group+0x44/0x50 kernel/exit.c:990
 do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x43ff48
Code: 00 00 be 3c 00 00 00 eb 19 66 0f 1f 84 00 00 00 00 00 48 89 d7 89 f0 0f 05 48 3d 00 f0 ff ff 77 21 f4 48 89 d7 44 89 c0 0f 05 <48> 3d 00 f0 ff ff 76 e0 f7 d8 64 41 89 01 eb d8 0f 1f 84 00 00 00
RSP: 002b:00007ffda863a7f8 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 000000000043ff48
RDX: 0000000000000000 RSI: 000000000000003c RDI: 0000000000000000
RBP: 00000000004bfa70 R08: 00000000000000e7 R09: ffffffffffffffd0
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
R13: 00000000006d2180 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 10231:
 save_stack+0x23/0x90 mm/kasan/common.c:71
 set_track mm/kasan/common.c:79 [inline]
 __kasan_kmalloc mm/kasan/common.c:489 [inline]
 __kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:462
 kasan_slab_alloc+0xf/0x20 mm/kasan/common.c:497
 slab_post_alloc_hook mm/slab.h:437 [inline]
 slab_alloc mm/slab.c:3326 [inline]
 kmem_cache_alloc+0x11a/0x6f0 mm/slab.c:3488
 kmem_cache_zalloc include/linux/slab.h:732 [inline]
 alloc_vfsmnt+0x28/0x780 fs/namespace.c:182
 vfs_create_mount+0x96/0x500 fs/namespace.c:961
 __do_sys_fsmount fs/namespace.c:3423 [inline]
 __se_sys_fsmount fs/namespace.c:3340 [inline]
 __x64_sys_fsmount+0x584/0xc80 fs/namespace.c:3340
 do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 16:
 save_stack+0x23/0x90 mm/kasan/common.c:71
 set_track mm/kasan/common.c:79 [inline]
 __kasan_slab_free+0x102/0x150 mm/kasan/common.c:451
 kasan_slab_free+0xe/0x10 mm/kasan/common.c:459
 __cache_free mm/slab.c:3432 [inline]
 kmem_cache_free+0x86/0x260 mm/slab.c:3698
 free_vfsmnt+0x6f/0x90 fs/namespace.c:559
 delayed_free_vfsmnt+0x16/0x20 fs/namespace.c:564
 __rcu_reclaim kernel/rcu/rcu.h:222 [inline]
 rcu_do_batch kernel/rcu/tree.c:2092 [inline]
 invoke_rcu_callbacks kernel/rcu/tree.c:2310 [inline]
 rcu_core+0xba5/0x1500 kernel/rcu/tree.c:2291
 __do_softirq+0x25c/0x94c kernel/softirq.c:292

The buggy address belongs to the object at ffff88809f99e800
 which belongs to the cache mnt_cache of size 432
The buggy address is located 292 bytes inside of
 432-byte region [ffff88809f99e800, ffff88809f99e9b0)
The buggy address belongs to the page:
page:ffffea00027e6780 refcount:1 mapcount:0 mapping:ffff8880aa594940 index:0x0
flags: 0x1fffc0000000200(slab)
raw: 01fffc0000000200 ffffea0002809908 ffffea000298af88 ffff8880aa594940
raw: 0000000000000000 ffff88809f99e000 0000000100000008 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff88809f99e800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88809f99e880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88809f99e900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                               ^
 ffff88809f99e980: fb fb fb fb fb fb fc fc fc fc fc fc fc fc fc fc
 ffff88809f99ea00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
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