A new null-ptr-deref Write bug in snd_pcm_format_set_silence
From: butt3rflyh4ck
Date: Sun Sep 04 2022 - 05:49:20 EST
Hi, there is a new null-ptr-deref Write bug in
snd_pcm_format_set_slience in sound/core/pcm_misc.c in the latest
upstream kernel and can reproduce it.
We call SNDCTL_DSP_SYNC and SNDCTL_DSP_SPEED in multiple threads to
trigger the vulnerability.
See the Call Trace:
==================================================================
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
kasan_report+0xb1/0x1e0 mm/kasan/report.c:495
check_region_inline mm/kasan/generic.c:183 [inline]
kasan_check_range+0x13d/0x180 mm/kasan/generic.c:189
memset+0x20/0x40 mm/kasan/shadow.c:44
snd_pcm_format_set_silence sound/core/pcm_misc.c:441 [inline]
snd_pcm_format_set_silence+0x215/0x350 sound/core/pcm_misc.c:424
snd_pcm_oss_sync+0x60e/0x800 sound/core/oss/pcm_oss.c:1690
snd_pcm_oss_ioctl+0x2087/0x3420 sound/core/oss/pcm_oss.c:2634
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:870 [inline]
__se_sys_ioctl fs/ioctl.c:856 [inline]
__x64_sys_ioctl+0x193/0x200 fs/ioctl.c:856
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
==================================================================
We can see the function snd_pcm_format_set_silence code below:
```
int snd_pcm_format_set_silence(snd_pcm_format_t format, void *data,
unsigned int samples)
{
int width;
unsigned char *dst;
const unsigned char *pat;
if (!valid_format(format))
return -EINVAL;
if (samples == 0)
return 0;
width = pcm_formats[(INT)format].phys; /* physical width */
pat = pcm_formats[(INT)format].silence;
if (!width || !pat)
return -EINVAL;
/* signed or 1 byte data */
if (pcm_formats[(INT)format].signd == 1 || width <= 8) {
unsigned int bytes = samples * width / 8;
memset(data, *pat, bytes); ///// [1] ---------> data is NULL
return 0;
}
......
}
```
[1], the data pointer is NULL, we can know snd_pcm_format_set_silence
called in line 1690 in sound/core/oss/pcm_oss.c from call stack trace.
let we see code below:
```
static int snd_pcm_oss_sync(struct snd_pcm_oss_file *pcm_oss_file)
{
int err = 0;
unsigned int saved_f_flags;
struct snd_pcm_substream *substream;
struct snd_pcm_runtime *runtime;
snd_pcm_format_t format;
unsigned long width;
size_t size;
substream = pcm_oss_file->streams[SNDRV_PCM_STREAM_PLAYBACK];
if (substream != NULL) {
runtime = substream->runtime;
if (atomic_read(&substream->mmap_count))
goto __direct;
err = snd_pcm_oss_make_ready(substream);
if (err < 0)
return err;
atomic_inc(&runtime->oss.rw_ref);
if (mutex_lock_interruptible(&runtime->oss.params_lock)) {
atomic_dec(&runtime->oss.rw_ref);
return -ERESTARTSYS;
}
format = snd_pcm_oss_format_from(runtime->oss.format);
width = snd_pcm_format_physical_width(format);
if (runtime->oss.buffer_used > 0) {
#ifdef OSS_DEBUG
pcm_dbg(substream->pcm, "sync: buffer_used\n");
#endif
size = (8 * (runtime->oss.period_bytes -
runtime->oss.buffer_used) + 7) / width;
snd_pcm_format_set_silence(format,
runtime->oss.buffer
+ runtime->oss.buffer_used, ///// [2]
size);
err = snd_pcm_oss_sync1(substream,
runtime->oss.period_bytes);
if (err < 0)
goto unlock;
} else if (runtime->oss.period_ptr > 0) {
```
[2] runtime->oss.buffer + runtime->oss.buffer_used is the data
pointer, but runtime->oss.buffer is NULL here but it doesn't make
sense.
runtime->oss.buffter is allocated by kvzalloc, if runtime->oss_buffer
is NULL, it would return an ENOMEM error.
Maybe I think there is a race condition, the runtime->oss.buffer is
freed and set to NULL but we can use runtime->oss.buffter via ioctl.
###reproduce it
[ 167.258988][T25615]
==================================================================
[ 167.265917][T25615] BUG: KASAN: null-ptr-deref in
snd_pcm_format_set_silence+0x215/0x350
[ 167.266704][T25615] Write of size 16383 at addr 0000000000000001 by
task snd_pcm_format_/25615
[ 167.267506][T25615]
[ 167.267732][T25615] CPU: 0 PID: 25615 Comm: snd_pcm_format_ Not
tainted 6.0.0-rc3-00299-gd895ec7938c4 #11
[ 167.268617][T25615] Hardware name: QEMU Standard PC (i440FX + PIIX,
1996), BIOS 1.14.0-2 04/01/2014
[ 167.269410][T25615] Call Trace:
[ 167.269697][T25615] <TASK>
[ 167.269977][T25615] dump_stack_lvl+0xcd/0x134
[ 167.270428][T25615] ? snd_pcm_format_set_silence+0x215/0x350
[ 167.270985][T25615] kasan_report+0xb1/0x1e0
[ 167.271405][T25615] ? snd_pcm_format_set_silence+0x215/0x350
[ 167.271964][T25615] kasan_check_range+0x13d/0x180
[ 167.272440][T25615] memset+0x20/0x40
[ 167.272809][T25615] snd_pcm_format_set_silence+0x215/0x350
[ 167.273366][T25615] snd_pcm_oss_sync+0x60e/0x800
[ 167.273831][T25615] snd_pcm_oss_ioctl+0x2087/0x3420
[ 167.274320][T25615] ? snd_pcm_oss_release+0x300/0x300
[ 167.274817][T25615] ? __fget_files+0x26a/0x440
[ 167.275262][T25615] ? bpf_lsm_file_ioctl+0x5/0x10
[ 167.275731][T25615] ? snd_pcm_oss_release+0x300/0x300
[ 167.276222][T25615] __x64_sys_ioctl+0x193/0x200
[ 167.276677][T25615] do_syscall_64+0x35/0xb0
[ 167.277108][T25615] entry_SYSCALL_64_after_hwframe+0x63/0xcd
[ 167.277679][T25615] RIP: 0033:0x44af9d
[ 167.278058][T25615] Code: 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 f3
0f 1e fa 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 b8 ff ff 8
[ 167.279792][T25615] RSP: 002b:00007f0cb636a178 EFLAGS: 00000246
ORIG_RAX: 0000000000000010
[ 167.280546][T25615] RAX: ffffffffffffffda RBX: 0000000000000000
RCX: 000000000044af9d
[ 167.281285][T25615] RDX: 0000000000000000 RSI: 0000000000005001
RDI: 0000000000000003
[ 167.282001][T25615] RBP: 00007f0cb636a1a0 R08: 0000000000000000
R09: 0000000000000000
[ 167.282715][T25615] R10: 0000000000000000 R11: 0000000000000246
R12: 00007ffcfea8e08e
[ 167.283432][T25615] R13: 00007ffcfea8e08f R14: 0000000000000000
R15: 00007f0cb636a640
[ 167.284164][T25615] </TASK>
[ 167.284453][T25615]
==================================================================
If needed I would provide a reproduce.
Regards,
butt3rflyh4ck.
--
Active Defense Lab of Venustech