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

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: d2a22790 Add linux-next specific files for 20200412
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=11fa5020100000
kernel config: https://syzkaller.appspot.com/x/.config?x=602913252b851ac7
dashboard link: https://syzkaller.appspot.com/bug?extid=72868dd424eb66c6b95f
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1656abb3e00000

The bug was bisected to:

commit 69879c01a0c3f70e0887cfb4d9ff439814361e46
Author: Eric W. Biederman <ebie...@xmission.com>
Date: Thu Feb 20 14:08:20 2020 +0000

proc: Remove the now unnecessary internal mount of proc

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=1474cde7e00000
final crash: https://syzkaller.appspot.com/x/report.txt?x=1674cde7e00000
console output: https://syzkaller.appspot.com/x/log.txt?x=1274cde7e00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+72868d...@syzkaller.appspotmail.com
Fixes: 69879c01a0c3 ("proc: Remove the now unnecessary internal mount of proc")

proc_fill_super: allocate dentry failed
==================================================================
BUG: KASAN: use-after-free in fast_dput fs/dcache.c:727 [inline]
BUG: KASAN: use-after-free in dput+0x53e/0xdf0 fs/dcache.c:846
Read of size 4 at addr ffff88808a618cf0 by task syz-executor.0/8426

CPU: 0 PID: 8426 Comm: syz-executor.0 Not tainted 5.6.0-next-20200412-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+0xd3/0x315 mm/kasan/report.c:382
__kasan_report.cold+0x35/0x4d mm/kasan/report.c:511
kasan_report+0x33/0x50 mm/kasan/common.c:625
fast_dput fs/dcache.c:727 [inline]
dput+0x53e/0xdf0 fs/dcache.c:846
proc_kill_sb+0x73/0xf0 fs/proc/root.c:195
deactivate_locked_super+0x8c/0xf0 fs/super.c:335
vfs_get_super+0x258/0x2d0 fs/super.c:1212
vfs_get_tree+0x89/0x2f0 fs/super.c:1547
do_new_mount fs/namespace.c:2813 [inline]
do_mount+0x1306/0x1b30 fs/namespace.c:3138
__do_sys_mount fs/namespace.c:3347 [inline]
__se_sys_mount fs/namespace.c:3324 [inline]
__x64_sys_mount+0x18f/0x230 fs/namespace.c:3324
do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295
entry_SYSCALL_64_after_hwframe+0x49/0xb3
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:00007ffc1930ec48 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 0000000001324914 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 8404:
save_stack+0x1b/0x40 mm/kasan/common.c:49
set_track mm/kasan/common.c:57 [inline]
__kasan_kmalloc mm/kasan/common.c:495 [inline]
__kasan_kmalloc.constprop.0+0xbf/0xd0 mm/kasan/common.c:468
slab_post_alloc_hook mm/slab.h:586 [inline]
slab_alloc mm/slab.c:3320 [inline]
kmem_cache_alloc+0x11b/0x740 mm/slab.c:3484
__d_alloc+0x2b/0x8e0 fs/dcache.c:1690
d_alloc+0x4a/0x240 fs/dcache.c:1769
d_alloc_name+0x80/0xb0 fs/dcache.c:1831
proc_setup_self+0xe4/0x3c0 fs/proc/self.c:44
proc_fill_super+0x3fb/0x660 fs/proc/root.c:133
vfs_get_super+0x12e/0x2d0 fs/super.c:1191
vfs_get_tree+0x89/0x2f0 fs/super.c:1547
do_new_mount fs/namespace.c:2813 [inline]
do_mount+0x1306/0x1b30 fs/namespace.c:3138
__do_sys_mount fs/namespace.c:3347 [inline]
__se_sys_mount fs/namespace.c:3324 [inline]
__x64_sys_mount+0x18f/0x230 fs/namespace.c:3324
do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295
entry_SYSCALL_64_after_hwframe+0x49/0xb3

Freed by task 9:
save_stack+0x1b/0x40 mm/kasan/common.c:49
set_track mm/kasan/common.c:57 [inline]
kasan_set_free_info mm/kasan/common.c:317 [inline]
__kasan_slab_free+0xf7/0x140 mm/kasan/common.c:456
__cache_free mm/slab.c:3426 [inline]
kmem_cache_free+0x7f/0x320 mm/slab.c:3694
rcu_do_batch kernel/rcu/tree.c:2206 [inline]
rcu_core+0x59f/0x1370 kernel/rcu/tree.c:2433
__do_softirq+0x26c/0x9f7 kernel/softirq.c:292

The buggy address belongs to the object at ffff88808a618cf0
which belongs to the cache dentry of size 304
The buggy address is located 0 bytes inside of
304-byte region [ffff88808a618cf0, ffff88808a618e20)
The buggy address belongs to the page:
page:ffffea0002298600 refcount:1 mapcount:0 mapping:000000001a027ea8 index:0x0
flags: 0xfffe0000000200(slab)
raw: 00fffe0000000200 ffffea00022985c8 ffffea0002298648 ffff88821bc50540
raw: 0000000000000000 ffff88808a618000 000000010000000b 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff88808a618b80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff88808a618c00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff88808a618c80: 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fb fb
^
ffff88808a618d00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88808a618d80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


---
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