Re: KASAN: invalid-free in snd_seq_port_disconnect

[Takashi Iwai <tiwai@suse.de>]

On Thu, 30 Jul 2020 13:44:14 +0200,
Hillf Danton wrote:
> 
> 
> Wed, 29 Jul 2020 22:53:21 -0700
> > syzbot found the following issue on:
> > 
> > HEAD commit:    d3590ebf Merge tag 'audit-pr-20200729' of git://git.kernel..
> > git tree:       upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=1797d388900000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=812bbfcb6ae2cd60
> > dashboard link: https://syzkaller.appspot.com/bug?extid=9d2abfef257f3e2d4713
> > compiler:       clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14761be4900000
> > 
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+9d2abfef257f3e2d4713@syzkaller.appspotmail.com
> > 
> > ==================================================================
> > BUG: KASAN: double-free or invalid-free in snd_seq_port_disconnect+0x570/0x610 sound/core/seq/seq_ports.c:614
> > 
> > CPU: 1 PID: 7530 Comm: syz-executor.0 Not tainted 5.8.0-rc7-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+0x1f0/0x31e lib/dump_stack.c:118
> >  print_address_description+0x66/0x5a0 mm/kasan/report.c:383
> >  kasan_report_invalid_free+0x54/0xd0 mm/kasan/report.c:477
> >  __kasan_slab_free+0xae/0x170 mm/kasan/common.c:443
> >  __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
> > RIP: 0033:0x45c429
> > Code: 8d 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 5b b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
> > RSP: 002b:00007f25d0cb3c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> > RAX: ffffffffffffffda RBX: 00000000000154c0 RCX: 000000000045c429
> > RDX: 0000000000000000 RSI: 0000000000005100 RDI: 0000000000000003
> > RBP: 000000000078bfd8 R08: 0000000000000000 R09: 0000000000000000
> > R10: 0000000000000000 R11: 0000000000000246 R12: 000000000078bfac
> > R13: 00007ffe03b9f5df R14: 00007f25d0cb49c0 R15: 000000000078bfac
> > 
> > Allocated by task 7529:
> >  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 7529:
> >  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 ffff8880a3acdd00
> >  which belongs to the cache kmalloc-128 of size 128
> > The buggy address is located 0 bytes inside of
> >  128-byte region [ffff8880a3acdd00, ffff8880a3acdd80)
> > The buggy address belongs to the page:
> > page:ffffea00028eb340 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0
> > flags: 0xfffe0000000200(slab)
> > raw: 00fffe0000000200 ffffea00025c5208 ffffea0002a371c8 ffff8880aa400700
> > raw: 0000000000000000 ffff8880a3acd000 0000000100000010 0000000000000000
> > page dumped because: kasan: bad access detected
> > 
> > Memory state around the buggy address:
> >  ffff8880a3acdc00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> >  ffff8880a3acdc80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> > >ffff8880a3acdd00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> >                    ^
> >  ffff8880a3acdd80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> >  ffff8880a3acde00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> > ==================================================================
> 
> Serialize the open and ioctl pathes using the register_mutex lock.
> 
> --- 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

This should fix this bug report and another similar one, indeed.
Please submit a proper patch once when you get a positive result.


Thanks!

Takashi