I have tested this patch, it works well. Regards, butt3rflyh4ck. On Sun, Sep 4, 2022 at 6:27 PM Takashi Iwai <tiwai@xxxxxxx> wrote: > > 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) { -- Active Defense Lab of Venustech