KASAN: use-after-free Read in bpf_cgroup_storage_release

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: fc2a3b5dd618 Merge branch 'bpf-cgroup-local-storage'
git tree: bpf-next
console output: https://syzkaller.appspot.com/x/log.txt?x=17a6a1c8400000
kernel config: https://syzkaller.appspot.com/x/.config?x=3bfcc1651962483
dashboard link: https://syzkaller.appspot.com/bug?extid=25554ab865a12b51c66f
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=12c4b9b4400000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13e9d6f0400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+25554a...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in debug_spin_lock_before
kernel/locking/spinlock_debug.c:83 [inline]
BUG: KASAN: use-after-free in do_raw_spin_lock+0x1c0/0x200
kernel/locking/spinlock_debug.c:112
Read of size 4 at addr ffff8801c4723644 by task syz-executor865/9746

CPU: 0 PID: 9746 Comm: syz-executor865 Not tainted 4.18.0-rc5+ #68
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+0x242/0x2fe mm/kasan/report.c:412
__asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:432
debug_spin_lock_before kernel/locking/spinlock_debug.c:83 [inline]
do_raw_spin_lock+0x1c0/0x200 kernel/locking/spinlock_debug.c:112
__raw_spin_lock_bh include/linux/spinlock_api_smp.h:136 [inline]
_raw_spin_lock_bh+0x39/0x40 kernel/locking/spinlock.c:168
spin_lock_bh include/linux/spinlock.h:315 [inline]
bpf_cgroup_storage_release+0x2c/0x110 kernel/bpf/local_storage.c:276
free_used_maps+0x81/0x200 kernel/bpf/syscall.c:961
bpf_prog_load+0x17ba/0x1c90 kernel/bpf/syscall.c:1414
__do_sys_bpf kernel/bpf/syscall.c:2338 [inline]
__se_sys_bpf kernel/bpf/syscall.c:2300 [inline]
__x64_sys_bpf+0x36c/0x510 kernel/bpf/syscall.c:2300
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4490d9
Code: e8 8c bb 02 00 48 83 c4 18 c3 0f 1f 80 00 00 00 00 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 4b 00 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f6096d1ace8 EFLAGS: 00000246 ORIG_RAX: 0000000000000141
RAX: ffffffffffffffda RBX: 00000000006e5a08 RCX: 00000000004490d9
RDX: 0000000000000048 RSI: 000000002001a840 RDI: 0000000000000005
RBP: 00000000006e5a00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006e5a0c
R13: 00007fffd579e24f R14: 00007f6096d1b9c0 R15: 0000000000000019

Allocated by task 9746:
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
kmem_cache_alloc_node_trace+0x150/0x770 mm/slab.c:3663
kmalloc_node include/linux/slab.h:551 [inline]
cgroup_storage_map_alloc+0x26d/0x400 kernel/bpf/local_storage.c:209
find_and_alloc_map kernel/bpf/syscall.c:129 [inline]
map_create+0x37f/0xe20 kernel/bpf/syscall.c:481
__do_sys_bpf kernel/bpf/syscall.c:2323 [inline]
__se_sys_bpf kernel/bpf/syscall.c:2300 [inline]
__x64_sys_bpf+0x303/0x510 kernel/bpf/syscall.c:2300
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 19:
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
cgroup_storage_map_free+0x16e/0x210 kernel/bpf/local_storage.c:234
bpf_map_free_deferred+0xba/0xf0 kernel/bpf/syscall.c:290
process_one_work+0xc73/0x1ba0 kernel/workqueue.c:2153
worker_thread+0x189/0x13c0 kernel/workqueue.c:2296
kthread+0x345/0x410 kernel/kthread.c:246
ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:412

The buggy address belongs to the object at ffff8801c4723540
which belongs to the cache kmalloc-512 of size 512
The buggy address is located 260 bytes inside of
512-byte region [ffff8801c4723540, ffff8801c4723740)
The buggy address belongs to the page:
page:ffffea000711c8c0 count:1 mapcount:0 mapping:ffff8801dac00940
index:0xffff8801c4723a40
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffffea0007299088 ffffea00072247c8 ffff8801dac00940
raw: ffff8801c4723a40 ffff8801c4723040 0000000100000004 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8801c4723500: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
ffff8801c4723580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff8801c4723600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff8801c4723680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8801c4723700: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
==================================================================


---
This bug is generated by a bot. It may contain errors.
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[Daniel Borkmann]

[ +Roman ]

[Roman Gushchin]

On Thu, Aug 02, 2018 at 09:23:00PM +0200, Daniel Borkmann wrote:
> [ +Roman ]
>
> On 08/02/2018 07:59 PM, syzbot wrote:
> > Hello,
> >
> > syzbot found the following crash on:
> >
> > HEAD commit:    fc2a3b5dd618 Merge branch 'bpf-cgroup-local-storage'
> > git tree:       bpf-next

> > console output: https://urldefense.proofpoint.com/v2/url?u=https-3A__syzkaller.appspot.com_x_log.txt-3Fx-3D17a6a1c8400000&d=DwIDaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=jJYgtDM7QT-W-Fz_d29HYQ&m=EDSyTXUjQWi0Wr-pal_Z622tnk3UnxrZ318k9Tct4wQ&s=kNpA8CkCvXgMPDNNfqgkqDlGShzYMrSvH1AWBdBslJo&e=
> > kernel config:  https://urldefense.proofpoint.com/v2/url?u=https-3A__syzkaller.appspot.com_x_.config-3Fx-3D3bfcc1651962483&d=DwIDaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=jJYgtDM7QT-W-Fz_d29HYQ&m=EDSyTXUjQWi0Wr-pal_Z622tnk3UnxrZ318k9Tct4wQ&s=PYjD3Jqpwgzv3cBV64k8EAbXwdolWkrrrcanCfJU6KQ&e=
> > dashboard link: https://urldefense.proofpoint.com/v2/url?u=https-3A__syzkaller.appspot.com_bug-3Fextid-3D25554ab865a12b51c66f&d=DwIDaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=jJYgtDM7QT-W-Fz_d29HYQ&m=EDSyTXUjQWi0Wr-pal_Z622tnk3UnxrZ318k9Tct4wQ&s=FQHY4B4Ok0SJh_C-lkToT7mX_Ehj3NSHe6Fe1UiL--Y&e=

> > compiler:       gcc (GCC) 8.0.1 20180413 (experimental)

> > syzkaller repro:https://urldefense.proofpoint.com/v2/url?u=https-3A__syzkaller.appspot.com_x_repro.syz-3Fx-3D12c4b9b4400000&d=DwIDaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=jJYgtDM7QT-W-Fz_d29HYQ&m=EDSyTXUjQWi0Wr-pal_Z622tnk3UnxrZ318k9Tct4wQ&s=38j2eoBTEgFiU2FlYHK86YXiVNEjxV6n3ug4tlAZ3MQ&e=
> > C reproducer:   https://urldefense.proofpoint.com/v2/url?u=https-3A__syzkaller.appspot.com_x_repro.c-3Fx-3D13e9d6f0400000&d=DwIDaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=jJYgtDM7QT-W-Fz_d29HYQ&m=EDSyTXUjQWi0Wr-pal_Z622tnk3UnxrZ318k9Tct4wQ&s=R75neIjoG9ODJgTDAUAfWqORwwOVX0k_cz7NsKyF6qw&e=

So, it looks like we drop the last refcount on local storage map
from release_maps() and schedule bpf_map_free_deferred(), which
runs prior to bpf_cgroup_storage_release() in free_used_maps().

If so, here is the fix:

diff --git a/kernel/bpf/local_storage.c b/kernel/bpf/local_storage.c
index cd0b115c2395..fc4e37f68f2a 100644
--- a/kernel/bpf/local_storage.c
+++ b/kernel/bpf/local_storage.c
@@ -277,6 +277,7 @@ void bpf_cgroup_storage_release(struct bpf_prog *prog, struct bpf_map *_map)
if (map->prog == prog) {
WARN_ON(prog->aux->cgroup_storage != _map);
map->prog = NULL;
+ prog->aux->cgroup_storage = NULL;
}
spin_unlock_bh(&map->lock);
}

--

I'll post an updated version (v7) in few minutes.

Thanks to syzbot team for the report!

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger
crash:

Reported-and-tested-by:
syzbot+25554a...@syzkaller.appspotmail.com

Tested on:

commit: 82c018d734a7 Merge branch 'bpf-cgroup-local-storage'
git tree: bpf-next
kernel config: https://syzkaller.appspot.com/x/.config?x=3bfcc1651962483

compiler: gcc (GCC) 8.0.1 20180413 (experimental)

Note: testing is done by a robot and is best-effort only.

[Daniel Borkmann]

On 08/02/2018 07:59 PM, syzbot wrote:

> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit:    fc2a3b5dd618 Merge branch 'bpf-cgroup-local-storage'
> git tree:       bpf-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=17a6a1c8400000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=3bfcc1651962483
> dashboard link: https://syzkaller.appspot.com/bug?extid=25554ab865a12b51c66f
> compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
> syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=12c4b9b4400000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13e9d6f0400000
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+25554a...@syzkaller.appspotmail.com

#syz fix: 82c018d734a7 Merge branch 'bpf-cgroup-local-storage'

[Dmitry Vyukov]

#syz fix: Merge branch 'bpf-cgroup-local-storage'