KASAN: use-after-free Read in do_shrink_slab

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 1f7a4c73a739 Merge tag '9p-for-4.19-2' of git://github.com..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16c46d9a400000
kernel config: https://syzkaller.appspot.com/x/.config?x=68e80edb3c9718c5
dashboard link: https://syzkaller.appspot.com/bug?extid=d5f648a1bfe15678786b
compiler: gcc (GCC) 8.0.1 20180413 (experimental)

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

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+d5f648...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in do_shrink_slab+0xbd4/0xcb0 mm/vmscan.c:456
Read of size 8 at addr ffff8801ae513558 by task syz-executor6/20506

CPU: 0 PID: 20506 Comm: syz-executor6 Not tainted 4.18.0+ #195
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+0x1c9/0x2b4 lib/dump_stack.c:113
print_address_description+0x6c/0x20b mm/kasan/report.c:256
kasan_report_error mm/kasan/report.c:354 [inline]
kasan_report.cold.7+0x242/0x30d mm/kasan/report.c:412
__asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433
do_shrink_slab+0xbd4/0xcb0 mm/vmscan.c:456
shrink_slab_memcg mm/vmscan.c:600 [inline]
shrink_slab+0x7b7/0x990 mm/vmscan.c:673
shrink_node+0x429/0x16a0 mm/vmscan.c:2734
shrink_zones mm/vmscan.c:2963 [inline]
do_try_to_free_pages+0x3e7/0x1290 mm/vmscan.c:3025
try_to_free_mem_cgroup_pages+0x49d/0xc90 mm/vmscan.c:3323
memory_high_write+0x283/0x310 mm/memcontrol.c:5399
cgroup_file_write+0x31f/0x840 kernel/cgroup/cgroup.c:3447
kernfs_fop_write+0x2ba/0x480 fs/kernfs/file.c:316
__vfs_write+0x117/0x9d0 fs/read_write.c:485
__kernel_write+0x10c/0x380 fs/read_write.c:506
write_pipe_buf+0x181/0x240 fs/splice.c:798
splice_from_pipe_feed fs/splice.c:503 [inline]
__splice_from_pipe+0x38e/0x7c0 fs/splice.c:627
splice_from_pipe+0x1ea/0x340 fs/splice.c:662
default_file_splice_write+0x3c/0x90 fs/splice.c:810
do_splice_from fs/splice.c:852 [inline]
direct_splice_actor+0x128/0x190 fs/splice.c:1019
splice_direct_to_actor+0x318/0x8f0 fs/splice.c:974
do_splice_direct+0x2d4/0x420 fs/splice.c:1062
do_sendfile+0x623/0xe20 fs/read_write.c:1440
__do_sys_sendfile64 fs/read_write.c:1501 [inline]
__se_sys_sendfile64 fs/read_write.c:1487 [inline]
__x64_sys_sendfile64+0x1fd/0x250 fs/read_write.c:1487
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x457089
Code: fd b4 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 cb b4 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f7151c7ac78 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 00007f7151c7b6d4 RCX: 0000000000457089
RDX: 0000000000000000 RSI: 0000000000000005 RDI: 0000000000000004
RBP: 00000000009300a0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000004d3cb0 R14: 00000000004c8769 R15: 0000000000000000

Allocated by task 19741:
save_stack+0x43/0xd0 mm/kasan/kasan.c:448
set_track mm/kasan/kasan.c:460 [inline]
kasan_kmalloc+0xc4/0xe0 mm/kasan/kasan.c:553
__do_kmalloc mm/slab.c:3718 [inline]
__kmalloc+0x14e/0x760 mm/slab.c:3727
kmalloc_array include/linux/slab.h:635 [inline]
kcalloc include/linux/slab.h:646 [inline]
iter_file_splice_write+0x25d/0x1010 fs/splice.c:693
do_splice_from fs/splice.c:852 [inline]
direct_splice_actor+0x128/0x190 fs/splice.c:1019
splice_direct_to_actor+0x318/0x8f0 fs/splice.c:974
do_splice_direct+0x2d4/0x420 fs/splice.c:1062
do_sendfile+0x623/0xe20 fs/read_write.c:1440
__do_sys_sendfile64 fs/read_write.c:1495 [inline]
__se_sys_sendfile64 fs/read_write.c:1487 [inline]
__x64_sys_sendfile64+0x15d/0x250 fs/read_write.c:1487
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 19741:
save_stack+0x43/0xd0 mm/kasan/kasan.c:448
set_track mm/kasan/kasan.c:460 [inline]
__kasan_slab_free+0x11a/0x170 mm/kasan/kasan.c:521
kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528
__cache_free mm/slab.c:3498 [inline]
kfree+0xd9/0x260 mm/slab.c:3813
iter_file_splice_write+0x78d/0x1010 fs/splice.c:777
do_splice_from fs/splice.c:852 [inline]
direct_splice_actor+0x128/0x190 fs/splice.c:1019
splice_direct_to_actor+0x318/0x8f0 fs/splice.c:974
do_splice_direct+0x2d4/0x420 fs/splice.c:1062
do_sendfile+0x623/0xe20 fs/read_write.c:1440
__do_sys_sendfile64 fs/read_write.c:1495 [inline]
__se_sys_sendfile64 fs/read_write.c:1487 [inline]
__x64_sys_sendfile64+0x15d/0x250 fs/read_write.c:1487
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8801ae513500
which belongs to the cache kmalloc-256 of size 256
The buggy address is located 88 bytes inside of
256-byte region [ffff8801ae513500, ffff8801ae513600)
The buggy address belongs to the page:
page:ffffea0006b944c0 count:1 mapcount:0 mapping:ffff8801dac007c0
index:0xffff8801ae513b40
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffffea000701dd48 ffff8801dac01638 ffff8801dac007c0
raw: ffff8801ae513b40 ffff8801ae513000 000000010000000a 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8801ae513400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8801ae513480: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
> ffff8801ae513500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff8801ae513580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8801ae513600: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
==================================================================


---
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syzbot.

[Kirill Tkhai]

There is a sad BUG introduced in patch adding SHRINKER_REGISTERING.
shrinker_idr business is only for memcg-aware shrinkers. Only
such type of shrinkers have id and they must be finaly installed
via idr_replace() in this function. For !memcg-aware shrinkers
we never initialize shrinker->id field.

But there are all types of shrinkers passed to idr_replace(),
and every !memcg-aware shrinker with random ID (most probably,
its id is 0) replaces memcg-aware shrinker pointed by the ID
in IDR.

This patch fixes the problem.

Reported-by: syzbot+d5f648...@syzkaller.appspotmail.com
Fixes: 7e010df53c80 "mm: use special value SHRINKER_REGISTERING instead of list_empty() check"
Signed-off-by: Kirill Tkhai <ktk...@virtuozzo.com>
---
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 4375b1e9bd56..3c6e2bfee427 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -408,7 +408,8 @@ void register_shrinker_prepared(struct shrinker *shrinker)
down_write(&shrinker_rwsem);
list_add_tail(&shrinker->list, &shrinker_list);
#ifdef CONFIG_MEMCG_KMEM
- idr_replace(&shrinker_idr, shrinker, shrinker->id);
+ if (shrinker->flags & SHRINKER_MEMCG_AWARE)
+ idr_replace(&shrinker_idr, shrinker, shrinker->id);
#endif
up_write(&shrinker_rwsem);
}