KASAN: use-after-free Read in delete_and_unsubscribe_port (2)

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    7cc2a8ea Merge tag 'block-5.8-2020-07-01' of git://git.ker..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11561e7b100000
kernel config:  https://syzkaller.appspot.com/x/.config?x=7be693511b29b338
dashboard link: https://syzkaller.appspot.com/bug?extid=1a54a94bd32716796edd
compiler:       gcc (GCC) 10.1.0-syz 20200507
userspace arch: i386

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+1a54a94bd32716796edd at syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in list_empty include/linux/list.h:282 [inline]
BUG: KASAN: use-after-free in delete_and_unsubscribe_port+0x420/0x4f0 sound/core/seq/seq_ports.c:530
Read of size 8 at addr ffff88809533de50 by task syz-executor.0/29034

CPU: 0 PID: 29034 Comm: syz-executor.0 Not tainted 5.8.0-rc3-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+0x18f/0x20d lib/dump_stack.c:118
 print_address_description.constprop.0.cold+0xae/0x436 mm/kasan/report.c:383
 __kasan_report mm/kasan/report.c:513 [inline]
 kasan_report.cold+0x1f/0x37 mm/kasan/report.c:530
 list_empty include/linux/list.h:282 [inline]
 delete_and_unsubscribe_port+0x420/0x4f0 sound/core/seq/seq_ports.c:530
 snd_seq_port_disconnect+0x433/0x5c0 sound/core/seq/seq_ports.c:610
 snd_seq_ioctl_unsubscribe_port+0x1fc/0x400 sound/core/seq/seq_clientmgr.c:1525
 snd_seq_ioctl+0x202/0x3e0 sound/core/seq/seq_clientmgr.c:2157
 snd_seq_ioctl_compat+0xdc/0x2d0 sound/core/seq/seq_compat.c:109
 __do_compat_sys_ioctl+0x1d3/0x230 fs/ioctl.c:847
 do_syscall_32_irqs_on+0x3f/0x60 arch/x86/entry/common.c:403
 __do_fast_syscall_32 arch/x86/entry/common.c:448 [inline]
 do_fast_syscall_32+0x7f/0x120 arch/x86/entry/common.c:474
 entry_SYSENTER_compat+0x6d/0x7c arch/x86/entry/entry_64_compat.S:138
RIP: 0023:0xf7ff0569
Code: Bad RIP value.
RSP: 002b:00000000f5deb0cc EFLAGS: 00000296 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000040505331
RDX: 0000000020000200 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 29030:
 save_stack+0x1b/0x40 mm/kasan/common.c:48
 set_track mm/kasan/common.c:56 [inline]
 __kasan_kmalloc.constprop.0+0xc2/0xd0 mm/kasan/common.c:494
 kmem_cache_alloc_trace+0x14f/0x2d0 mm/slab.c:3551
 kmalloc include/linux/slab.h:555 [inline]
 kzalloc include/linux/slab.h:669 [inline]
 snd_seq_port_connect+0x5d/0x520 sound/core/seq/seq_ports.c:553
 snd_seq_ioctl_subscribe_port+0x1fc/0x400 sound/core/seq/seq_clientmgr.c:1484
 snd_seq_ioctl+0x202/0x3e0 sound/core/seq/seq_clientmgr.c:2157
 snd_seq_ioctl_compat+0xdc/0x2d0 sound/core/seq/seq_compat.c:109
 __do_compat_sys_ioctl+0x1d3/0x230 fs/ioctl.c:847
 do_syscall_32_irqs_on+0x3f/0x60 arch/x86/entry/common.c:403
 __do_fast_syscall_32 arch/x86/entry/common.c:448 [inline]
 do_fast_syscall_32+0x7f/0x120 arch/x86/entry/common.c:474
 entry_SYSENTER_compat+0x6d/0x7c arch/x86/entry/entry_64_compat.S:138

Freed by task 29035:
 save_stack+0x1b/0x40 mm/kasan/common.c:48
 set_track mm/kasan/common.c:56 [inline]
 kasan_set_free_info mm/kasan/common.c:316 [inline]
 __kasan_slab_free+0xf5/0x140 mm/kasan/common.c:455
 __cache_free mm/slab.c:3426 [inline]
 kfree+0x103/0x2c0 mm/slab.c:3757
 snd_seq_port_disconnect+0x4c1/0x5c0 sound/core/seq/seq_ports.c:614
 snd_seq_ioctl_unsubscribe_port+0x1fc/0x400 sound/core/seq/seq_clientmgr.c:1525
 snd_seq_ioctl+0x202/0x3e0 sound/core/seq/seq_clientmgr.c:2157
 snd_seq_ioctl_compat+0xdc/0x2d0 sound/core/seq/seq_compat.c:109
 __do_compat_sys_ioctl+0x1d3/0x230 fs/ioctl.c:847
 do_syscall_32_irqs_on+0x3f/0x60 arch/x86/entry/common.c:403
 __do_fast_syscall_32 arch/x86/entry/common.c:448 [inline]
 do_fast_syscall_32+0x7f/0x120 arch/x86/entry/common.c:474
 entry_SYSENTER_compat+0x6d/0x7c arch/x86/entry/entry_64_compat.S:138

The buggy address belongs to the object at ffff88809533de00
 which belongs to the cache kmalloc-128 of size 128
The buggy address is located 80 bytes inside of
 128-byte region [ffff88809533de00, ffff88809533de80)
The buggy address belongs to the page:
page:ffffea000254cf40 refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff88809533d100
flags: 0xfffe0000000200(slab)
raw: 00fffe0000000200 ffffea00029c2e48 ffffea0002257d48 ffff8880aa000700
raw: ffff88809533d100 ffff88809533d000 000000010000000a 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff88809533dd00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88809533dd80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88809533de00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                 ^
 ffff88809533de80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88809533df00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


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