Date:   Fri, 09 Mar 2018 12:59:03 -0800
From:   syzbot <syzbot+4090700a4f13fccaf648@...kaller.appspotmail.com>
To:     alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
        mingo@...nel.org, o-takashi@...amocchi.jp, perex@...ex.cz,
        syzkaller-bugs@...glegroups.com, tiwai@...e.com,
        viro@...iv.linux.org.uk
Subject: KASAN: use-after-free Read in snd_pcm_oss_get_formats

Hello,

syzbot hit the following crash on upstream commit
1b88accf6a659c46d5c8e68912896f112bf882bb (Thu Mar 8 01:49:33 2018 +0000)
Merge tag 'for_linus' of  
git://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost

So far this crash happened 3 times on upstream.
C reproducer is attached.
syzkaller reproducer is attached.
Raw console output is attached.
compiler: gcc (GCC) 7.1.1 20170620
.config is attached.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+4090700a4f13fccaf648@...kaller.appspotmail.com
It will help syzbot understand when the bug is fixed. See footer for  
details.
If you forward the report, please keep this part and the footer.

IPVS: ftp: loaded support on port[0] = 21
audit: type=1400 audit(1520612143.836:8): avc:  denied  { map } for   
pid=4259 comm="syzkaller191035" path="/dev/dsp1" dev="devtmpfs" ino=1250  
scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023  
tcontext=system_u:object_r:sound_device_t:s0 tclass=chr_file permissive=1
IPVS: ftp: loaded support on port[0] = 21
IPVS: ftp: loaded support on port[0] = 21
==================================================================
BUG: KASAN: use-after-free in snd_mask_test include/sound/pcm_params.h:141  
[inline]
BUG: KASAN: use-after-free in snd_pcm_oss_get_formats+0x320/0x380  
sound/core/oss/pcm_oss.c:1770
Read of size 4 at addr ffff8801bace4024 by task syzkaller191035/4271

CPU: 0 PID: 4271 Comm: syzkaller191035 Not tainted 4.16.0-rc4+ #346
IPVS: ftp: loaded support on port[0] = 21
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
  __dump_stack lib/dump_stack.c:17 [inline]
  dump_stack+0x194/0x24d lib/dump_stack.c:53
IPVS: ftp: loaded support on port[0] = 21
  print_address_description+0x73/0x250 mm/kasan/report.c:256
  kasan_report_error mm/kasan/report.c:354 [inline]
  kasan_report+0x23c/0x360 mm/kasan/report.c:412
  __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:432
  snd_mask_test include/sound/pcm_params.h:141 [inline]
  snd_pcm_oss_get_formats+0x320/0x380 sound/core/oss/pcm_oss.c:1770
  snd_pcm_oss_set_format sound/core/oss/pcm_oss.c:1784 [inline]
  snd_pcm_oss_ioctl+0x1e2f/0x39f0 sound/core/oss/pcm_oss.c:2515
IPVS: ftp: loaded support on port[0] = 21
IPVS: ftp: loaded support on port[0] = 21
  vfs_ioctl fs/ioctl.c:46 [inline]
  do_vfs_ioctl+0x1b1/0x1520 fs/ioctl.c:686
  SYSC_ioctl fs/ioctl.c:701 [inline]
  SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
  do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
  entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x4499e9
RSP: 002b:00007fa1872a5da8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000006dbc24 RCX: 00000000004499e9
RDX: 0000000020000080 RSI: 00800000c0045005 RDI: 0000000000000003
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dbc20
R13: 7073642f7665642f R14: 00800000c0045005 R15: 0000000000000003

Allocated by task 4271:
  save_stack+0x43/0xd0 mm/kasan/kasan.c:447
  set_track mm/kasan/kasan.c:459 [inline]
  kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:552
  kmem_cache_alloc_trace+0x136/0x740 mm/slab.c:3607
  kmalloc include/linux/slab.h:512 [inline]
  snd_pcm_oss_get_formats+0x1c7/0x380 sound/core/oss/pcm_oss.c:1760
  snd_pcm_oss_set_format sound/core/oss/pcm_oss.c:1784 [inline]
  snd_pcm_oss_ioctl+0x1e2f/0x39f0 sound/core/oss/pcm_oss.c:2515
  vfs_ioctl fs/ioctl.c:46 [inline]
  do_vfs_ioctl+0x1b1/0x1520 fs/ioctl.c:686
  SYSC_ioctl fs/ioctl.c:701 [inline]
  SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
  do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
  entry_SYSCALL_64_after_hwframe+0x42/0xb7

Freed by task 4271:
  save_stack+0x43/0xd0 mm/kasan/kasan.c:447
  set_track mm/kasan/kasan.c:459 [inline]
  __kasan_slab_free+0x11a/0x170 mm/kasan/kasan.c:520
  kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:527
  __cache_free mm/slab.c:3485 [inline]
  kfree+0xd9/0x260 mm/slab.c:3800
  snd_pcm_oss_get_formats+0x216/0x380 sound/core/oss/pcm_oss.c:1766
  snd_pcm_oss_set_format sound/core/oss/pcm_oss.c:1784 [inline]
  snd_pcm_oss_ioctl+0x1e2f/0x39f0 sound/core/oss/pcm_oss.c:2515
  vfs_ioctl fs/ioctl.c:46 [inline]
  do_vfs_ioctl+0x1b1/0x1520 fs/ioctl.c:686
  SYSC_ioctl fs/ioctl.c:701 [inline]
  SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
  do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
  entry_SYSCALL_64_after_hwframe+0x42/0xb7

The buggy address belongs to the object at ffff8801bace4000
  which belongs to the cache kmalloc-1024 of size 1024
The buggy address is located 36 bytes inside of
  1024-byte region [ffff8801bace4000, ffff8801bace4400)
The buggy address belongs to the page:
page:ffffea0006eb3900 count:1 mapcount:0 mapping:ffff8801bace4000 index:0x0  
compound_mapcount: 0
flags: 0x2fffc0000008100(slab|head)
raw: 02fffc0000008100 ffff8801bace4000 0000000000000000 0000000100000007
raw: ffffea000761d7a0 ffffea0006eb39a0 ffff8801dac00ac0 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
  ffff8801bace3f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
  ffff8801bace3f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ffff8801bace4000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                ^
  ffff8801bace4080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
  ffff8801bace4100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


---
This bug is generated by a dumb bot. It may contain errors.
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