KASAN: invalid-free in snd_seq_port_disconnect

Hillf Danton hdanton at sina.com
Thu Jul 30 13:44:14 CEST 2020 

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 at 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

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