Re: [alsa-devel] [PATCH] ASoC: dmaengine: Make the pcm->name equal to pcm->id if the name is not set

[Takashi Iwai <tiwai@suse.de>]

On Tue, 10 Sep 2019 16:23:59 +0200,
Peter Ujfalusi wrote:
> 
> 
> 
> On 10/09/2019 15.07, Takashi Iwai wrote:
> > On Fri, 06 Sep 2019 07:55:24 +0200,
> > Peter Ujfalusi wrote:
> >>
> >> Some tools use the snd_pcm_info_get_name() to try to identify PCMs or for
> >> other purposes.
> >>
> >> Currently it is left empty with the dmaengine-pcm, in this case copy the
> >> pcm->id string as pcm->name.
> >>
> >> For example IGT is using this to find the HDMI PCM for testing audio on it.
> >>
> >> Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
> >> Reported-by: Arthur She <arthur.she@linaro.org>
> >> ---
> >> Hi,
> >>
> >> this was actually reported for 4.14 kernel with omap-pcm (replaced by sdma-pcm
> >> in v4.18), since then we only use the generic dmaengine PCM but the same issue
> >> applies today.
> >>
> >> Regards,
> >> Peter
> >>
> >>  sound/soc/soc-generic-dmaengine-pcm.c | 6 ++++++
> >>  1 file changed, 6 insertions(+)
> >>
> >> diff --git a/sound/soc/soc-generic-dmaengine-pcm.c b/sound/soc/soc-generic-dmaengine-pcm.c
> >> index 748f5f641002..d93db2c2b527 100644
> >> --- a/sound/soc/soc-generic-dmaengine-pcm.c
> >> +++ b/sound/soc/soc-generic-dmaengine-pcm.c
> >> @@ -306,6 +306,12 @@ static int dmaengine_pcm_new(struct snd_soc_pcm_runtime *rtd)
> >>  
> >>  		if (!dmaengine_pcm_can_report_residue(dev, pcm->chan[i]))
> >>  			pcm->flags |= SND_DMAENGINE_PCM_FLAG_NO_RESIDUE;
> >> +
> >> +		if (rtd->pcm->streams[i].pcm->name[0] == '\0') {
> >> +			strncpy(rtd->pcm->streams[i].pcm->name,
> >> +				rtd->pcm->streams[i].pcm->id,
> >> +				sizeof(rtd->pcm->streams[i].pcm->name));
> >> +		}
> > 
> > Any reason to use strncpy() instead of strscpy()?
> > After merging Mark's branch, I got a compile warning like:
> >   sound/soc/soc-generic-dmaengine-pcm.c:311:4: warning: 'strncpy'
> >   accessing 80 bytes at offsets 88 and 24 may overlap up to 0 bytes at
> >   offset [9223372036854775807, -9223372036854775808] [-Wrestrict]
> 
> I have not seen such a warning.
> 'may overlap up to 0 bytes' ?
> snd_pcm_info {
> ...
>         unsigned char id[64];           /* ID (user selectable) */
>         unsigned char name[80];         /* name of this device */
>         unsigned char subname[32];      /* subdevice name */
> ...
> };
> 
> and strncpy() supposed to be something like this:
> char * strncpy(char *dest, const char *src, size_t n)
> {
> 	size_t i;
> 
> 	for (i = 0; i < n && src[i] != '\0'; i++)
> 		dest[i] = src[i];
> 	for ( ; i < n; i++)
> 		dest[i] = '\0';
> 
> 	return dest;
> }
> 
> I can see if I can get my compilers to show the warning and try
> strscpy() if it helps on it.

strncpy() doesn't guarantee the string termination if you pass the
exact buffer size.  Better to use strscpy() in such a case.


thanks,

Takashi
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