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SubjectKASAN: invalid-free in snd_seq_port_disconnect
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Hello,

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
==================================================================


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
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syzbot can test patches for this issue, for details see:
https://goo.gl/tpsmEJ#testing-patches

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