Hello,

syzbot found the following crash on:

HEAD commit: 8fe28cb58bcb Linux 4.20 git tree: upstream console output: https://syzkaller.appspot.com/x/log.txt?x=166859b3400000 kernel config: https://syzkaller.appspot.com/x/.config?x=7d581260bae0899a dashboard link: https://syzkaller.appspot.com/bug?extid=9917f000776fb73fa40f compiler: gcc (GCC) 8.0.1 20180413 (experimental)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit: Reported-by: syzbot+9917f000776fb73fa40f@syzkaller.appspotmail.com

================================================================== BUG: KASAN: use-after-free in __read_once_size include/linux/compiler.h:191 [inline] BUG: KASAN: use-after-free in list_empty include/linux/list.h:226 [inline] BUG: KASAN: use-after-free in delete_and_unsubscribe_port+0x5d7/0x6d0 sound/core/seq/seq_ports.c:548 Read of size 8 at addr ffff8881d1c05590 by task syz-executor1/6930

CPU: 0 PID: 6930 Comm: syz-executor1 Not tainted 4.20.0 #167 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+0x1d3/0x2c6 lib/dump_stack.c:113 print_address_description.cold.8+0x9/0x1ff mm/kasan/report.c:256 kasan_report_error mm/kasan/report.c:354 [inline] kasan_report.cold.9+0x242/0x309 mm/kasan/report.c:412 __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433 __read_once_size include/linux/compiler.h:191 [inline] list_empty include/linux/list.h:226 [inline] delete_and_unsubscribe_port+0x5d7/0x6d0 sound/core/seq/seq_ports.c:548 snd_seq_port_disconnect+0x17b/0x280 sound/core/seq/seq_ports.c:628 snd_seq_ioctl_unsubscribe_port+0x1d8/0x310 sound/core/seq/seq_clientmgr.c:1499 snd_seq_ioctl+0x253/0x440 sound/core/seq/seq_clientmgr.c:2138 vfs_ioctl fs/ioctl.c:46 [inline] file_ioctl fs/ioctl.c:509 [inline] do_vfs_ioctl+0x1de/0x1790 fs/ioctl.c:696 ksys_ioctl+0xa9/0xd0 fs/ioctl.c:713 __do_sys_ioctl fs/ioctl.c:720 [inline] __se_sys_ioctl fs/ioctl.c:718 [inline] __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290 entry_SYSCALL_64_after_hwframe+0x49/0xbe RIP: 0033:0x457759 Code: fd b3 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 cb b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00 RSP: 002b:00007f36626cac78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000457759 RDX: 00000000200001c0 RSI: 0000000040505331 RDI: 0000000000000003 RBP: 000000000073bf00 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 00007f36626cb6d4 R13: 00000000004ca358 R14: 00000000004d35d0 R15: 00000000ffffffff

Allocated by task 6924: save_stack+0x43/0xd0 mm/kasan/kasan.c:448 set_track mm/kasan/kasan.c:460 [inline] kasan_kmalloc+0xc7/0xe0 mm/kasan/kasan.c:553 kmem_cache_alloc_trace+0x152/0x750 mm/slab.c:3620 kmalloc include/linux/slab.h:546 [inline] kzalloc include/linux/slab.h:741 [inline] snd_seq_port_connect+0xe0/0x760 sound/core/seq/seq_ports.c:571 snd_seq_ioctl_subscribe_port+0x1d8/0x310 sound/core/seq/seq_clientmgr.c:1458 snd_seq_ioctl+0x253/0x440 sound/core/seq/seq_clientmgr.c:2138 vfs_ioctl fs/ioctl.c:46 [inline] file_ioctl fs/ioctl.c:509 [inline] do_vfs_ioctl+0x1de/0x1790 fs/ioctl.c:696 ksys_ioctl+0xa9/0xd0 fs/ioctl.c:713 __do_sys_ioctl fs/ioctl.c:720 [inline] __se_sys_ioctl fs/ioctl.c:718 [inline] __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 6931: save_stack+0x43/0xd0 mm/kasan/kasan.c:448 set_track mm/kasan/kasan.c:460 [inline] __kasan_slab_free+0x102/0x150 mm/kasan/kasan.c:521 kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528 __cache_free mm/slab.c:3498 [inline] kfree+0xcf/0x230 mm/slab.c:3817 snd_seq_port_disconnect+0x205/0x280 sound/core/seq/seq_ports.c:632 snd_seq_ioctl_unsubscribe_port+0x1d8/0x310 sound/core/seq/seq_clientmgr.c:1499 snd_seq_ioctl+0x253/0x440 sound/core/seq/seq_clientmgr.c:2138 vfs_ioctl fs/ioctl.c:46 [inline] file_ioctl fs/ioctl.c:509 [inline] do_vfs_ioctl+0x1de/0x1790 fs/ioctl.c:696 ksys_ioctl+0xa9/0xd0 fs/ioctl.c:713 __do_sys_ioctl fs/ioctl.c:720 [inline] __se_sys_ioctl fs/ioctl.c:718 [inline] __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290 entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8881d1c05540 which belongs to the cache kmalloc-128 of size 128 The buggy address is located 80 bytes inside of 128-byte region [ffff8881d1c05540, ffff8881d1c055c0) The buggy address belongs to the page: page:ffffea0007470140 count:1 mapcount:0 mapping:ffff8881da800640 index:0xffff8881d1c05b40 flags: 0x2fffc0000000200(slab) raw: 02fffc0000000200 ffffea0006fb09c8 ffffea0006f38908 ffff8881da800640 raw: ffff8881d1c05b40 ffff8881d1c05000 000000010000000e 0000000000000000 page dumped because: kasan: bad access detected

Memory state around the buggy address: ffff8881d1c05480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff8881d1c05500: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb

ffff8881d1c05580: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc

^ ffff8881d1c05600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff8881d1c05680: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb ==================================================================

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