On Tue, 12 Oct 2021 18:41:19 +0200,
Pierre-Louis Bossart wrote:
>
>
>
> On 10/12/21 10:27 AM, Takashi Iwai wrote:
> > On Tue, 12 Oct 2021 17:15:56 +0200,
> > Pierre-Louis Bossart wrote:
> >>
> >>> In either way, the new_ptr has to be validated beforehand that it's
> >>> within 0..boundary-1. (old_ptr is assumed to be valid.)
> >>
> >> In the 3 of the calls to pcm_lib_apply_appl_ptr(), the check is done
> >> already prior to calling that function
> >> if (appl_ptr >= runtime->boundary)
> >> appl_ptr -= runtime->boundary;
> >> err = pcm_lib_apply_appl_ptr(substream, appl_ptr);
> >>
> >>
> >> it's rather unclear to me why the same check is not done for sync_ptr, e.g.
> >>
> >> if (!(sync_ptr.flags & SNDRV_PCM_SYNC_PTR_APPL)) {
> >> err = pcm_lib_apply_appl_ptr(substream,
> >> sync_ptr.c.control.appl_ptr);
> >>
> >> if (!(sflags & SNDRV_PCM_SYNC_PTR_APPL)) {
> >> err = pcm_lib_apply_appl_ptr(substream,
> >> scontrol.appl_ptr);
> >>
> >> Should I add a check there, or add a check inside of
> >> pcm_lib_apply_appl_ptr() which would be a duplicate in the majority of
> >> cases?
> >
> > I guess adding in pcm_lib_appl_appl_ptr() would be easier and safer.
> > There is even one more place that is calling pcm_lib_apply_appl_ptr()
> > in the very latest commit (a fix for a buggy 32bit compat ioctl).
>
> ok, here's the code I'll start testing. Thanks a lot Takashi for your help.
>
> diff --git a/sound/core/pcm_lib.c b/sound/core/pcm_lib.c
> index a144a3f68e9e..e839459916ca 100644
> --- a/sound/core/pcm_lib.c
> +++ b/sound/core/pcm_lib.c
> @@ -2127,11 +2127,30 @@ int pcm_lib_apply_appl_ptr(struct
> snd_pcm_substream *substream,
> {
> struct snd_pcm_runtime *runtime = substream->runtime;
> snd_pcm_uframes_t old_appl_ptr = runtime->control->appl_ptr;
> + snd_pcm_sframes_t diff;
> int ret;
>
> if (old_appl_ptr == appl_ptr)
> return 0;
>
> + /*
> + * check if a rewind is requested by the application, after
> + * verifying the new appl_ptr is in the 0..boundary range
> + */
> + if (substream->runtime->info & SNDRV_PCM_INFO_NO_REWINDS) {
> + if (appl_ptr >= runtime->boundary)
> + appl_ptr -= runtime->boundary;
The boundary check can (or should) be done unconditionally.
It was too naive to assume a sane appl_ptr passed always.
And, it can rather return an error. So,
if (appl_ptr >= runtime->boundary)
return -EINVAL;
/* check if a rewind is requested by the application */
if (substream->runtime->info & SNDRV_PCM_INFO_NO_REWINDS) {
diff = appl_ptr - old_appl_ptr;
....
> + if (diff >= 0) {
> + if (diff > runtime->buffer_size)
> + return 0;
> + } else {
> + if (runtime->boundary + diff > runtime->buffer_size)
> + return 0;
I'm not sure whether we should return 0 here. In snd_pcm_rewind() it
returns 0 due to application breakage, though.
thanks,
Takashi
