* KASAN: use-after-free Read in snd_pcm_timer_resolution
@ 2018-03-29 23:01 syzbot
2018-04-02 21:06 ` Takashi Iwai
0 siblings, 1 reply; 2+ messages in thread
From: syzbot @ 2018-03-29 23:01 UTC (permalink / raw)
To: alsa-devel, colin.king, linux-kernel, perex, syzkaller-bugs, tiwai
Hello,
syzbot hit the following crash on upstream commit
0b412605ef5f5c64b31f19e2910b1d5eba9929c3 (Thu Mar 29 01:07:23 2018 +0000)
Merge tag 'drm-fixes-for-v4.16-rc8' of
git://people.freedesktop.org/~airlied/linux
syzbot dashboard link:
https://syzkaller.appspot.com/bug?extid=8e62ff4e07aa2ce87826
So far this crash happened 3 times on upstream.
C reproducer: https://syzkaller.appspot.com/x/repro.c?id=6219387178582016
syzkaller reproducer:
https://syzkaller.appspot.com/x/repro.syz?id=5176598244360192
Raw console output:
https://syzkaller.appspot.com/x/log.txt?id=5815694612496384
Kernel config:
https://syzkaller.appspot.com/x/.config?id=-8440362230543204781
compiler: gcc (GCC) 7.1.1 20170620
IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+8e62ff4e07aa2ce87826@syzkaller.appspotmail.com
It will help syzbot understand when the bug is fixed. See footer for
details.
If you forward the report, please keep this part and the footer.
==================================================================
BUG: KASAN: use-after-free in snd_pcm_timer_resolution+0xa3/0xc0
sound/core/pcm_timer.c:72
Read of size 4 at addr ffff8801bdd58490 by task syzkaller702213/13238
CPU: 0 PID: 13238 Comm: syzkaller702213 Not tainted 4.16.0-rc7+ #370
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:17 [inline]
dump_stack+0x194/0x24d lib/dump_stack.c:53
print_address_description+0x73/0x250 mm/kasan/report.c:256
kasan_report_error mm/kasan/report.c:354 [inline]
kasan_report+0x23c/0x360 mm/kasan/report.c:412
__asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:432
snd_pcm_timer_resolution+0xa3/0xc0 sound/core/pcm_timer.c:72
snd_timer_resolution sound/core/timer.c:439 [inline]
snd_timer_notify1+0x10f/0x400 sound/core/timer.c:462
snd_timer_start1+0x586/0x8f0 sound/core/timer.c:522
snd_timer_start+0x5d/0xa0 sound/core/timer.c:634
snd_timer_user_start.isra.12+0xde/0x130 sound/core/timer.c:1878
snd_timer_user_continue sound/core/timer.c:1902 [inline]
__snd_timer_user_ioctl+0x1771/0x2c10 sound/core/timer.c:1977
snd_timer_user_ioctl+0x5f/0x7d sound/core/timer.c:1992
vfs_ioctl fs/ioctl.c:46 [inline]
do_vfs_ioctl+0x1b1/0x1520 fs/ioctl.c:686
SYSC_ioctl fs/ioctl.c:701 [inline]
SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x4453c9
RSP: 002b:00007ffd46abffe8 EFLAGS: 00000217 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00000000004453c9
RDX: 00000000004453c9 RSI: 00000000000054a2 RDI: 0000000000000003
RBP: 0000000000000000 R08: 0000000046ac0168 R09: 0000000046ac0168
R10: 0000000046ac0168 R11: 0000000000000217 R12: 00000000000142ea
R13: 0000000000402c90 R14: 00000000006d1440 R15: 0000000000000000
Allocated by task 13234:
save_stack+0x43/0xd0 mm/kasan/kasan.c:447
set_track mm/kasan/kasan.c:459 [inline]
kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:552
kmem_cache_alloc_trace+0x136/0x740 mm/slab.c:3608
kmalloc include/linux/slab.h:512 [inline]
kzalloc include/linux/slab.h:701 [inline]
snd_pcm_attach_substream+0x3c5/0xb60 sound/core/pcm.c:1006
snd_pcm_open_substream+0x95/0x3b0 sound/core/pcm_native.c:2372
snd_pcm_oss_open_file sound/core/oss/pcm_oss.c:2309 [inline]
snd_pcm_oss_open+0x7cf/0x1540 sound/core/oss/pcm_oss.c:2391
soundcore_open+0x321/0x630 sound/sound_core.c:597
chrdev_open+0x257/0x730 fs/char_dev.c:417
do_dentry_open+0x667/0xd40 fs/open.c:752
vfs_open+0x107/0x220 fs/open.c:866
do_last fs/namei.c:3379 [inline]
path_openat+0x1151/0x3530 fs/namei.c:3519
do_filp_open+0x25b/0x3b0 fs/namei.c:3554
do_sys_open+0x502/0x6d0 fs/open.c:1059
SYSC_openat fs/open.c:1086 [inline]
SyS_openat+0x30/0x40 fs/open.c:1080
do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
entry_SYSCALL_64_after_hwframe+0x42/0xb7
Freed by task 13234:
save_stack+0x43/0xd0 mm/kasan/kasan.c:447
set_track mm/kasan/kasan.c:459 [inline]
__kasan_slab_free+0x11a/0x170 mm/kasan/kasan.c:520
kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:527
__cache_free mm/slab.c:3486 [inline]
kfree+0xd9/0x260 mm/slab.c:3801
snd_pcm_detach_substream+0x134/0x290 sound/core/pcm.c:1057
snd_pcm_release_substream.part.44+0x23d/0x300 sound/core/pcm_native.c:2361
snd_pcm_release_substream+0x59/0x70 sound/core/pcm_native.c:2362
snd_pcm_oss_release_file.part.18+0x71/0xa0 sound/core/oss/pcm_oss.c:2268
snd_pcm_oss_release_file sound/core/oss/pcm_oss.c:2263 [inline]
snd_pcm_oss_release+0x104/0x280 sound/core/oss/pcm_oss.c:2448
__fput+0x327/0x7e0 fs/file_table.c:209
____fput+0x15/0x20 fs/file_table.c:243
task_work_run+0x199/0x270 kernel/task_work.c:113
exit_task_work include/linux/task_work.h:22 [inline]
do_exit+0x9bb/0x1ad0 kernel/exit.c:865
do_group_exit+0x149/0x400 kernel/exit.c:968
SYSC_exit_group kernel/exit.c:979 [inline]
SyS_exit_group+0x1d/0x20 kernel/exit.c:977
do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
entry_SYSCALL_64_after_hwframe+0x42/0xb7
The buggy address belongs to the object at ffff8801bdd58180
which belongs to the cache kmalloc-2048 of size 2048
The buggy address is located 784 bytes inside of
2048-byte region [ffff8801bdd58180, ffff8801bdd58980)
The buggy address belongs to the page:
page:ffffea0006f75600 count:1 mapcount:0 mapping:ffff8801bdd58180 index:0x0
compound_mapcount: 0
flags: 0x2fffc0000008100(slab|head)
raw: 02fffc0000008100 ffff8801bdd58180 0000000000000000 0000000100000003
raw: ffffea0007330d20 ffffea0007268aa0 ffff8801dac00c40 0000000000000000
page dumped because: kasan: bad access detected
Memory state around the buggy address:
ffff8801bdd58380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8801bdd58400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff8801bdd58480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff8801bdd58500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8801bdd58580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
---
This bug is generated by a dumb bot. It may contain errors.
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Direct all questions to syzkaller@googlegroups.com.
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If you forgot to add the Reported-by tag, once the fix for this bug is
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If you want to test a patch for this bug, please reply with:
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^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: KASAN: use-after-free Read in snd_pcm_timer_resolution
2018-03-29 23:01 KASAN: use-after-free Read in snd_pcm_timer_resolution syzbot
@ 2018-04-02 21:06 ` Takashi Iwai
0 siblings, 0 replies; 2+ messages in thread
From: Takashi Iwai @ 2018-04-02 21:06 UTC (permalink / raw)
To: alsa-devel; +Cc: colin.king, syzkaller-bugs, perex, linux-kernel
On Fri, 30 Mar 2018 01:01:01 +0200,
syzbot wrote:
>
> Hello,
>
> syzbot hit the following crash on upstream commit
> 0b412605ef5f5c64b31f19e2910b1d5eba9929c3 (Thu Mar 29 01:07:23 2018 +0000)
> Merge tag 'drm-fixes-for-v4.16-rc8' of
> git://people.freedesktop.org/~airlied/linux
> syzbot dashboard link:
> https://syzkaller.appspot.com/bug?extid=8e62ff4e07aa2ce87826
>
> So far this crash happened 3 times on upstream.
> C reproducer: https://syzkaller.appspot.com/x/repro.c?id=6219387178582016
> syzkaller reproducer:
> https://syzkaller.appspot.com/x/repro.syz?id=5176598244360192
> Raw console output:
> https://syzkaller.appspot.com/x/log.txt?id=5815694612496384
> Kernel config:
> https://syzkaller.appspot.com/x/.config?id=-8440362230543204781
> compiler: gcc (GCC) 7.1.1 20170620
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+8e62ff4e07aa2ce87826@syzkaller.appspotmail.com
> It will help syzbot understand when the bug is fixed. See footer for
> details.
> If you forward the report, please keep this part and the footer.
>
> ==================================================================
> BUG: KASAN: use-after-free in snd_pcm_timer_resolution+0xa3/0xc0
> sound/core/pcm_timer.c:72
> Read of size 4 at addr ffff8801bdd58490 by task syzkaller702213/13238
>
> CPU: 0 PID: 13238 Comm: syzkaller702213 Not tainted 4.16.0-rc7+ #370
> Hardware name: Google Google Compute Engine/Google Compute Engine,
> BIOS Google 01/01/2011
> Call Trace:
> __dump_stack lib/dump_stack.c:17 [inline]
> dump_stack+0x194/0x24d lib/dump_stack.c:53
> print_address_description+0x73/0x250 mm/kasan/report.c:256
> kasan_report_error mm/kasan/report.c:354 [inline]
> kasan_report+0x23c/0x360 mm/kasan/report.c:412
> __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:432
> snd_pcm_timer_resolution+0xa3/0xc0 sound/core/pcm_timer.c:72
> snd_timer_resolution sound/core/timer.c:439 [inline]
> snd_timer_notify1+0x10f/0x400 sound/core/timer.c:462
> snd_timer_start1+0x586/0x8f0 sound/core/timer.c:522
> snd_timer_start+0x5d/0xa0 sound/core/timer.c:634
> snd_timer_user_start.isra.12+0xde/0x130 sound/core/timer.c:1878
> snd_timer_user_continue sound/core/timer.c:1902 [inline]
> __snd_timer_user_ioctl+0x1771/0x2c10 sound/core/timer.c:1977
> snd_timer_user_ioctl+0x5f/0x7d sound/core/timer.c:1992
(snip)
So this looks like a race between ALSA PCM and ALSA timer interfaces.
When a PCM timer is accessed during closing the corresponding PCM
substream, it may lead to such a UAF.
The fix patch is below. I'll queue it after testing locally.
thanks,
Takashi
-- 8< --
From: Takashi Iwai <tiwai@suse.de>
Subject: [PATCH] ALSA: pcm: Fix UAF at PCM release via PCM timer access
The PCM runtime object is created and freed dynamically at PCM stream
open / close time. This is tracked via substream->runtime, and it's
cleared at snd_pcm_detach_substream().
The runtime object assignment is protected by PCM open_mutex, so for
all PCM operations, it's safely handled. However, each PCM substream
provides also an ALSA timer interface, and user-space can access to
this while closing a PCM substream. This may eventually lead to a
UAF, as snd_pcm_timer_resolution() tries to access the runtime while
clearing it in other side.
Fortunately, it's the only concurrent access from the PCM timer, and
it merely reads runtime->timer_resolution field. So, we can avoid the
race by reordering kfree() and wrapping the substream->runtime
clearance with the corresponding timer lock.
Reported-by: syzbot+8e62ff4e07aa2ce87826@syzkaller.appspotmail.com
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
---
sound/core/pcm.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/sound/core/pcm.c b/sound/core/pcm.c
index 09ee8c6b9f75..66ac89aad681 100644
--- a/sound/core/pcm.c
+++ b/sound/core/pcm.c
@@ -28,6 +28,7 @@
#include <sound/core.h>
#include <sound/minors.h>
#include <sound/pcm.h>
+#include <sound/timer.h>
#include <sound/control.h>
#include <sound/info.h>
@@ -1054,8 +1055,13 @@ void snd_pcm_detach_substream(struct snd_pcm_substream *substream)
snd_free_pages((void*)runtime->control,
PAGE_ALIGN(sizeof(struct snd_pcm_mmap_control)));
kfree(runtime->hw_constraints.rules);
- kfree(runtime);
+ /* Avoid concurrent access to runtime via PCM timer interface */
+ if (substream->timer)
+ spin_lock_irq(&substream->timer->lock);
substream->runtime = NULL;
+ if (substream->timer)
+ spin_unlock_irq(&substream->timer->lock);
+ kfree(runtime);
put_pid(substream->pid);
substream->pid = NULL;
substream->pstr->substream_opened--;
--
2.16.2
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2018-03-29 23:01 KASAN: use-after-free Read in snd_pcm_timer_resolution syzbot
2018-04-02 21:06 ` Takashi Iwai
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