On Sun, 04 Sep 2022 11:48:37 +0200, butt3rflyh4ck wrote: > > 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. Yeah, likely it's in a small race window between two calls. Could you try the patch below? thanks, Takashi --- --- a/sound/core/oss/pcm_oss.c +++ b/sound/core/oss/pcm_oss.c @@ -1672,14 +1672,14 @@ static int snd_pcm_oss_sync(struct snd_pcm_oss_file *pcm_oss_file) 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; } + err = snd_pcm_oss_make_ready_locked(substream); + if (err < 0) + goto unlock; format = snd_pcm_oss_format_from(runtime->oss.format); width = snd_pcm_format_physical_width(format); if (runtime->oss.buffer_used > 0) {