On Mon, 24 Aug 2015 12:17:40 +0200, Markus Osterhoff wrote:

Dear Takashi,

maybe I am mistaken or have not made my patch clear, please let me apologise.

• Takashi Iwai tiwai@suse.de [150824 08:30]:

...

On Sun, 23 Aug 2015 20:37:05 +0200, Markus Osterhoff wrote:

...

With commits bbbc7e85 and 751e2216, a for-loop was restated using list_for_each_entry(...); originally, a local pcm* was extracted from an array and checked against NULL, if not-NULL then passed along to snd_pcm_add_chmap_ctls(...).

For a history of the function in question, have a look at lines 2430ff for git diff v4.0 v4.1 sound/pci/hda/hda_codec.c

The two commits that touched this function are Commit bbbc7e8502c9 ("ALSA: hda - Allocate hda_pcm objects dynamically") Commit 751e2216899c ("ALSA: hda: fix possible null dereference")

where the latter only fixes the order of two fixes, but not the pcm / pcm->pcm confusion.

...

Thanks for the patch. But this was already fixed by commit 751e2216899c in 4.1-rc1.

So I re-checked and diff'ed against the current v4.2-rc8 and found that the if-statement reads, /sound/pci/hda/hda_codec.c, line 3172: if (!pcm || pcm->own_chmap || while I propose if (!pcm->pcm || pcm->own_chmap ||

Then your previous patch did exactly opposite :)

With the mentioned 751e2216899c I do get a NULL dereference (for whatever reason), because pcm->pcm can indeed by NULL inside the loop. Please reconsider the patch:

Actually you're trying to shoot two things in a shot, and it's confusing. What we need is to *add* the NULL check of pcm->pcm. It's basically different from replacing pcm NULL check itself. The pcm NULL check is superfluous, indeed, and can be removed. But it can be done in a different patch, or mention properly in the changelog.

Could you revisit your patch with the proper description?

thanks,

Takashi

...

Takashi

Thanks for your time, Markus

Signed-off-by: Markus Osterhoff linux-kernel@k-raum.org

sound/pci/hda/hda_codec.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sound/pci/hda/hda_codec.c b/sound/pci/hda/hda_codec.c index 5de3c5d..47206b9 100644 --- a/sound/pci/hda/hda_codec.c +++ b/sound/pci/hda/hda_codec.c @@ -3172,7 +3172,7 @@ static int add_std_chmaps(struct hda_codec *codec) struct snd_pcm_chmap *chmap; const struct snd_pcm_chmap_elem *elem;

•                   if (!pcm || pcm->own_chmap ||
  

•                   if (!pcm->pcm || pcm->own_chmap ||
                        !hinfo->substreams)
                            continue;
                    elem = hinfo->chmap ? hinfo->chmap : snd_pcm_std_chmaps;
  
  

On Mon, 24 Aug 2015 14:11:39 +0200, Markus Osterhoff wrote:

After a for-loop was replaced by list_for_each_entry, see Commit bbbc7e8502c9 ("ALSA: hda - Allocate hda_pcm objects dynamically"), Commit 751e2216899c ("ALSA: hda: fix possible null dereference"), a possible NULL pointer dereference has been introduced; this patch adds the NULL check on pcm->pcm, while leaving a potentially superfluous check on pcm itself untouched.

Signed-off-by: Markus Osterhoff linux-kernel@k-raum.org

The patch couldn't be applied cleanly because the tabs are replaced wrongly with spaces, so I applied it manually now. Please fix your MUA or the way to create a patch at the next time.

thanks,

Takashi

---

sound/pci/hda/hda_codec.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sound/pci/hda/hda_codec.c b/sound/pci/hda/hda_codec.c index 5de3c5d..d1a2cb6 100644 --- a/sound/pci/hda/hda_codec.c +++ b/sound/pci/hda/hda_codec.c @@ -3172,7 +3172,7 @@ static int add_std_chmaps(struct hda_codec *codec) struct snd_pcm_chmap *chmap; const struct snd_pcm_chmap_elem *elem;

•                   if (!pcm || pcm->own_chmap ||
  

•                   if (!pcm || !pcm->pcm || pcm->own_chmap ||
                        !hinfo->substreams)
                            continue;
                    elem = hinfo->chmap ? hinfo->chmap : snd_pcm_std_chmaps;