KASAN: use-after-free Write in snd_rawmidi_kernel_write1

butt3rflyh4ck
2020-05-07T08:04:50Z

I report a bug (in linux-5.7-rc1) found by syzkaller.

kernel config: https://github.com/butterflyhack/syzkaller-fuzz/blob/master/v5.7.0-rc1.config
reproducer: https://github.com/butterflyhack/syzkaller-fuzz/blob/master/repro.cprog

I test the reproducer in linux-5.7-rc4 and crash too.

crash log:
==================================================================
BUG: KASAN: use-after-free in _copy_from_user+0x113/0x1a0 lib/usercopy.c:13
Write of size 1 at addr ffff888069da43ca by task syz-executor611/6797

CPU: 0 PID: 6797 Comm: syz-executor611 Not tainted 5.7.0-rc1 #3
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
1.10.2-1ubuntu1 04/01/2014
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x188/0x20d lib/dump_stack.c:118
print_address_description.constprop.0.cold+0xd3/0x347 mm/kasan/report.c:382
__kasan_report.cold+0x35/0x4d mm/kasan/report.c:511
kasan_report+0x33/0x50 mm/kasan/common.c:625
check_memory_region_inline mm/kasan/generic.c:187 [inline]
check_memory_region+0x141/0x190 mm/kasan/generic.c:193
_copy_from_user+0x113/0x1a0 lib/usercopy.c:13
copy_from_user include/linux/uaccess.h:144 [inline]
snd_rawmidi_kernel_write1+0x320/0x6f0 sound/core/rawmidi.c:1363
snd_rawmidi_write+0x2e4/0xb80 sound/core/rawmidi.c:1429
__vfs_write+0x76/0x100 fs/read_write.c:495
vfs_write+0x268/0x5d0 fs/read_write.c:559
ksys_write+0x1ee/0x250 fs/read_write.c:612
do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295
entry_SYSCALL_64_after_hwframe+0x49/0xb3
RIP: 0033:0x4553a9
Code: 00 00 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 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 73 01 c3 48 c7 c1 bc ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f556b7f5cc8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00000000006d9588 RCX: 00000000004553a9
RDX: 00000000fffffc85 RSI: 0000000020000040 RDI: 0000000000000004
RBP: 00000000006d9580 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006d958c
R13: 0000000000000000 R14: 00000000006d9580 R15: 00007fff34bcb390

Allocated by task 6797:
save_stack+0x1b/0x40 mm/kasan/common.c:49
set_track mm/kasan/common.c:57 [inline]
__kasan_kmalloc mm/kasan/common.c:495 [inline]
__kasan_kmalloc.constprop.0+0xbf/0xd0 mm/kasan/common.c:468
kmalloc_node include/linux/slab.h:578 [inline]
kvmalloc_node+0x61/0xf0 mm/util.c:574
kvmalloc include/linux/mm.h:757 [inline]
kvzalloc include/linux/mm.h:765 [inline]
snd_rawmidi_runtime_create sound/core/rawmidi.c:141 [inline]
open_substream+0x33d/0x880 sound/core/rawmidi.c:285
rawmidi_open_priv+0x58e/0x6e0 sound/core/rawmidi.c:336
snd_rawmidi_open+0x455/0xb20 sound/core/rawmidi.c:433
snd_open+0x212/0x3d0 sound/core/sound.c:163
chrdev_open+0x219/0x5c0 fs/char_dev.c:414
do_dentry_open+0x4ba/0x1290 fs/open.c:797
do_open fs/namei.c:3229 [inline]
path_openat+0x1e59/0x27d0 fs/namei.c:3346
do_filp_open+0x192/0x260 fs/namei.c:3373
do_sys_openat2+0x585/0x7d0 fs/open.c:1148
do_sys_open+0xc3/0x140 fs/open.c:1164
do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295
entry_SYSCALL_64_after_hwframe+0x49/0xb3

Freed by task 6798:
save_stack+0x1b/0x40 mm/kasan/common.c:49
set_track mm/kasan/common.c:57 [inline]
kasan_set_free_info mm/kasan/common.c:317 [inline]
__kasan_slab_free+0x126/0x170 mm/kasan/common.c:456
slab_free_hook mm/slub.c:1445 [inline]
slab_free_freelist_hook+0xc4/0x1c0 mm/slub.c:1478
slab_free mm/slub.c:3035 [inline]
kfree+0xd8/0x330 mm/slub.c:4003
kvfree+0x42/0x50 mm/util.c:603
resize_runtime_buffer+0x29e/0x370 sound/core/rawmidi.c:677
snd_rawmidi_output_params+0x128/0x170 sound/core/rawmidi.c:690
snd_rawmidi_ioctl+0x544/0x5b0 sound/core/rawmidi.c:841
vfs_ioctl fs/ioctl.c:47 [inline]
ksys_ioctl+0x11a/0x180 fs/ioctl.c:763
__do_sys_ioctl fs/ioctl.c:772 [inline]
__se_sys_ioctl fs/ioctl.c:770 [inline]
__x64_sys_ioctl+0x6f/0xb0 fs/ioctl.c:770
do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295
entry_SYSCALL_64_after_hwframe+0x49/0xb3

The buggy address belongs to the object at ffff888069da4000
which belongs to the cache kmalloc-4k of size 4096
The buggy address is located 970 bytes inside of
4096-byte region [ffff888069da4000, ffff888069da5000)
The buggy address belongs to the page:
page:ffffea0001a76800 refcount:1 mapcount:0 mapping:00000000c136e8e7
index:0x0 head:ffffea0001a76800 order:3 compound_mapcount:0
compound_pincount:0
flags: 0xfffe0000010200(slab|head)
raw: 00fffe0000010200 dead000000000100 dead000000000122 ffff88806bc0c280
raw: 0000000000000000 0000000080040004 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff888069da4280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff888069da4300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff888069da4380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff888069da4400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff888069da4480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Regards,
butt3rflyh4ck