回复: [PATCH] ALSA: seq: KASAN: use-after-free Read in delete_and_unsubscribe_port

["Zhang, Qiang" <Qiang.Zhang@windriver.com>]

________________________________________
发件人: Takashi Iwai <tiwai@suse.de>
发送时间: 2020年8月1日 17:39
收件人: Zhang, Qiang
抄送: perex@perex.cz; tiwai@suse.com; alsa-devel@alsa-project.org; linux-kernel@vger.kernel.org
主题: Re: [PATCH] ALSA: seq: KASAN: use-after-free Read in delete_and_unsubscribe_port

On Sat, 01 Aug 2020 08:24:03 +0200,
<qiang.zhang@windriver.com> wrote:
>
> From: Zhang Qiang <qiang.zhang@windriver.com>
>
> There is a potential race window,when a task acquire "src->list_mutex"
> write sem,traverse the linked list to find "subs" objects through
> parameter "info" in snd_seq_port_disconnect and then release this
> write sem, before this task acquire write sem again,this write sem
> may be acquired by another task, and get the same "subs" object through
> the same "info" before, it could happen "use-after-free" later, so a
> simple solution is to delete the object from the linked list when it
> is found.
>
> BUG: KASAN: use-after-free in list_empty include/linux/list.h:282 [inline]
> BUG: KASAN: use-after-free in delete_and_unsubscribe_port+0x8b/0x450
> sound/core/seq/seq_ports.c:530
> Read of size 8 at addr ffff888098523060 by task syz-executor.0/7202
>
> Call Trace:
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0x1f0/0x31e lib/dump_stack.c:118
>  print_address_description+0x66/0x5a0 mm/kasan/report.c:383
>  __kasan_report mm/kasan/report.c:513 [inline]
>  kasan_report+0x132/0x1d0 mm/kasan/report.c:530
>  list_empty include/linux/list.h:282 [inline]
>  delete_and_unsubscribe_port+0x8b/0x450 sound/core/seq/seq_ports.c:530
>  snd_seq_port_disconnect+0x568/0x610 sound/core/seq/seq_ports.c:612
>  snd_seq_ioctl_unsubscribe_port+0x349/0x6c0 sound/core/seq/seq_clientmgr.c:1525
>  snd_seq_oss_midi_close+0x397/0x620 sound/core/seq/oss/seq_oss_midi.c:405
>  snd_seq_oss_synth_reset+0x335/0x8b0 sound/core/seq/oss/seq_oss_synth.c:406
>  snd_seq_oss_reset+0x5b/0x250 sound/core/seq/oss/seq_oss_init.c:435
>  snd_seq_oss_ioctl+0x5c2/0x1090 sound/core/seq/oss/seq_oss_ioctl.c:93
>  odev_ioctl+0x51/0x70 sound/core/seq/oss/seq_oss.c:174
>  vfs_ioctl fs/ioctl.c:48 [inline]
>  ksys_ioctl fs/ioctl.c:753 [inline]
>  __do_sys_ioctl fs/ioctl.c:762 [inline]
>  __se_sys_ioctl+0xf9/0x160 fs/ioctl.c:760
>  do_syscall_64+0x73/0xe0 arch/x86/entry/common.c:384
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> Allocated by task 7202:
>  save_stack mm/kasan/common.c:48 [inline]
>  set_track mm/kasan/common.c:56 [inline]
>  __kasan_kmalloc+0x103/0x140 mm/kasan/common.c:494
>  kmem_cache_alloc_trace+0x234/0x300 mm/slab.c:3551
>  kmalloc include/linux/slab.h:555 [inline]
>  kzalloc include/linux/slab.h:669 [inline]
>  snd_seq_port_connect+0x66/0x460 sound/core/seq/seq_ports.c:553
>  snd_seq_ioctl_subscribe_port+0x349/0x6c0 sound/core/seq/seq_clientmgr.c:1484
>  snd_seq_oss_midi_open+0x4db/0x830 sound/core/seq/oss/seq_oss_midi.c:364
>  snd_seq_oss_synth_setup_midi+0x108/0x510 sound/core/seq/oss/seq_oss_synth.c:269
>  snd_seq_oss_open+0x899/0xe90 sound/core/seq/oss/seq_oss_init.c:261
>  odev_open+0x5e/0x90 sound/core/seq/oss/seq_oss.c:125
>  chrdev_open+0x498/0x580 fs/char_dev.c:414
>  do_dentry_open+0x813/0x1070 fs/open.c:828
>  do_open fs/namei.c:3243 [inline]
>  path_openat+0x278d/0x37f0 fs/namei.c:3360
>  do_filp_open+0x191/0x3a0 fs/namei.c:3387
>  do_sys_openat2+0x463/0x770 fs/open.c:1179
>  do_sys_open fs/open.c:1195 [inline]
>  __do_sys_openat fs/open.c:1209 [inline]
>  __se_sys_openat fs/open.c:1204 [inline]
>  __x64_sys_openat+0x1c8/0x1f0 fs/open.c:1204
>  do_syscall_64+0x73/0xe0 arch/x86/entry/common.c:384
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> Freed by task 7203:
>  save_stack mm/kasan/common.c:48 [inline]
>  set_track mm/kasan/common.c:56 [inline]
>  kasan_set_free_info mm/kasan/common.c:316 [inline]
>  __kasan_slab_free+0x114/0x170 mm/kasan/common.c:455
>  __cache_free mm/slab.c:3426 [inline]
>  kfree+0x10a/0x220 mm/slab.c:3757
>  snd_seq_port_disconnect+0x570/0x610 sound/core/seq/seq_ports.c:614
>  snd_seq_ioctl_unsubscribe_port+0x349/0x6c0 sound/core/seq/seq_clientmgr.c:1525
>  snd_seq_oss_midi_close+0x397/0x620 sound/core/seq/oss/seq_oss_midi.c:405
>  snd_seq_oss_synth_reset+0x335/0x8b0 sound/core/seq/oss/seq_oss_synth.c:406
>  snd_seq_oss_reset+0x5b/0x250 sound/core/seq/oss/seq_oss_init.c:435
>  snd_seq_oss_ioctl+0x5c2/0x1090 sound/core/seq/oss/seq_oss_ioctl.c:93
>  odev_ioctl+0x51/0x70 sound/core/seq/oss/seq_oss.c:174
>  vfs_ioctl fs/ioctl.c:48 [inline]
>  ksys_ioctl fs/ioctl.c:753 [inline]
>  __do_sys_ioctl fs/ioctl.c:762 [inline]
>  __se_sys_ioctl+0xf9/0x160 fs/ioctl.c:760
>  do_syscall_64+0x73/0xe0 arch/x86/entry/common.c:384
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> The buggy address belongs to the object at ffff888098523000
>  which belongs to the cache kmalloc-128 of size 128
> The buggy address is located 96 bytes inside of
>  128-byte region [ffff888098523000, ffff888098523080)
> The buggy address belongs to the page:
> page:ffffea00026148c0 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0
> flags: 0xfffe0000000200(slab)
> raw: 00fffe0000000200 ffffea0002613988 ffffea000262c648 ffff8880aa400700
> raw: 0000000000000000 ffff888098523000 0000000100000010 0000000000000000
> page dumped because: kasan: bad access detected
>
> Memory state around the buggy address:
>  ffff888098522f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>  ffff888098522f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> >ffff888098523000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                                                        ^
>  ffff888098523080: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>  ffff888098523100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ==================================================================
>
> Reported-by: syzbot+1a54a94bd32716796edd@syzkaller.appspotmail.com
> Signed-off-by: Zhang Qiang <qiang.zhang@windriver.com>

>Thanks for the patch.  But I'm afraid that this change would break the
>existing behavior and might have a bad side-effect.

>It's likely the same issue as reported in another syzkaller report
>("KASAN: invalid-free in snd_seq_port_disconnect"), and Hillf's patch
>below should covert this as well.  Could you check whether it works?

yes It's should same issue, add mutex lock in odev_ioctl, ensure serialization.
however, it should not be necessary to mutually exclusive with open and close.



>thanks,

>Takashi

>---
>--- a/sound/core/seq/oss/seq_oss.c
>+++ b/sound/core/seq/oss/seq_oss.c
>@@ -167,11 +167,17 @@ odev_write(struct file *file, const char
 >static long
 >odev_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 >{
>+       long rc;
>      struct seq_oss_devinfo *dp;
>+
>+       mutex_lock(&register_mutex);
>       dp = file->private_data;
>        if (snd_BUG_ON(!dp))
>-               return -ENXIO;
>-       return snd_seq_oss_ioctl(dp, cmd, arg);
>+               rc = -ENXIO;
>+       else
>+               rc = snd_seq_oss_ioctl(dp, cmd, arg);
>+       mutex_unlock(&register_mutex);
>+       return rc;
 >}

 >#ifdef CONFIG_COMPAT