proc_fill_super: can't allocate /proc/self
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BUG: KASAN: use-after-free in fast_dput fs/dcache.c:727 [inline]
BUG: KASAN: use-after-free in dput.part.30+0x367/0xa60 fs/dcache.c:846
Read of size 4 at addr ffff888089661000 by task syz-executor.1/8911

CPU: 0 PID: 8911 Comm: syz-executor.1 Not tainted 5.6.0-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+0x128/0x182 lib/dump_stack.c:118
 print_address_description.constprop.8.cold.10+0x9/0x317 mm/kasan/report.c:374
 __kasan_report.cold.11+0x1c/0x34 mm/kasan/report.c:506
 kasan_report+0xe/0x20 mm/kasan/common.c:641
 fast_dput fs/dcache.c:727 [inline]
 dput.part.30+0x367/0xa60 fs/dcache.c:846
 proc_kill_sb+0x59/0xb0 fs/proc/root.c:195
 deactivate_locked_super+0x6f/0xc0 fs/super.c:335
 vfs_get_super+0x1f8/0x290 fs/super.c:1212
 vfs_get_tree+0x7e/0x2c0 fs/super.c:1547
 do_new_mount fs/namespace.c:2822 [inline]
 do_mount+0x10c3/0x1710 fs/namespace.c:3107
 __do_sys_mount fs/namespace.c:3316 [inline]
 __se_sys_mount fs/namespace.c:3293 [inline]
 __x64_sys_mount+0x15d/0x1b0 fs/namespace.c:3293
 do_syscall_64+0xc6/0x5e0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45c889
Code: ad b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 7b b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f651cdebc78 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007f651cdec6d4 RCX: 000000000045c889
RDX: 0000000020000140 RSI: 0000000020000040 RDI: 0000000000000000
RBP: 000000000076bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000003
R13: 0000000000000749 R14: 00000000004ca15a R15: 0000000000000013

Allocated by task 8896:
 save_stack+0x19/0x80 mm/kasan/common.c:72
 set_track mm/kasan/common.c:80 [inline]
 __kasan_kmalloc.constprop.17+0xc1/0xd0 mm/kasan/common.c:515
 slab_post_alloc_hook mm/slab.h:584 [inline]
 slab_alloc mm/slab.c:3320 [inline]
 kmem_cache_alloc+0x11b/0x740 mm/slab.c:3484
 __d_alloc+0x25/0x870 fs/dcache.c:1690
 d_alloc+0x3f/0x200 fs/dcache.c:1769
 d_alloc_name+0x70/0xa0 fs/dcache.c:1831
 proc_setup_self+0xde/0x370 fs/proc/self.c:44
 proc_fill_super+0x35c/0x590 fs/proc/root.c:133
 vfs_get_super+0xe8/0x290 fs/super.c:1191
 vfs_get_tree+0x7e/0x2c0 fs/super.c:1547
 do_new_mount fs/namespace.c:2822 [inline]
 do_mount+0x10c3/0x1710 fs/namespace.c:3107
 __do_sys_mount fs/namespace.c:3316 [inline]
 __se_sys_mount fs/namespace.c:3293 [inline]
 __x64_sys_mount+0x15d/0x1b0 fs/namespace.c:3293
 do_syscall_64+0xc6/0x5e0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 16:
 save_stack+0x19/0x80 mm/kasan/common.c:72
 set_track mm/kasan/common.c:80 [inline]
 kasan_set_free_info mm/kasan/common.c:337 [inline]
 __kasan_slab_free+0xf7/0x140 mm/kasan/common.c:476
 __cache_free mm/slab.c:3426 [inline]
 kmem_cache_free+0x7f/0x320 mm/slab.c:3694
 rcu_do_batch kernel/rcu/tree.c:2186 [inline]
 rcu_core+0x584/0x1290 kernel/rcu/tree.c:2410
 __do_softirq+0x26e/0x9b2 kernel/softirq.c:292

The buggy address belongs to the object at ffff888089661000
 which belongs to the cache dentry of size 288
The buggy address is located 0 bytes inside of
 288-byte region [ffff888089661000, ffff888089661120)
The buggy address belongs to the page:
page:ffffea0002259840 refcount:1 mapcount:0 mapping:ffff8880aa5f8a80 index:0xffff888089661b00
flags: 0xfffe0000000200(slab)
raw: 00fffe0000000200 ffffea00021612c8 ffffea0002293388 ffff8880aa5f8a80
raw: ffff888089661b00 ffff888089661000 0000000100000008 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff888089660f00: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
 ffff888089660f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888089661000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                   ^
 ffff888089661080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888089661100: fb fb fb fb fc fc fc fc fc fc fc fc 00 00 00 00
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