[alsa-devel] [PATCH] amixer: add support for TLV byte control read

[Takashi Iwai]

On Thu, 28 Jan 2016 05:25:09 +0100,
Vinod Koul wrote:
> 
> On Wed, Jan 27, 2016 at 07:49:00PM +0100, Takashi Iwai wrote:
> > On Wed, 27 Jan 2016 18:47:52 +0100,
> > Vinod Koul wrote:
> > > 
> > > On Fri, Jan 22, 2016 at 11:50:08AM +0100, Takashi Iwai wrote:
> > > > On Fri, 22 Jan 2016 10:56:48 +0100,
> > > > Vinod Koul wrote:
> > > > > > Hm, it has a check
> > > > > > 
> > > > > > static int snd_ctl_hw_elem_tlv(snd_ctl_t *handle, int op_flag,
> > > > > > 			       unsigned int numid,
> > > > > > 			       unsigned int *tlv, unsigned int tlv_size)
> > > > > > {
> > > > > > 	....
> > > > > > 		if (xtlv->tlv[1] + 2 * sizeof(unsigned int) > tlv_size) {
> > > > > > 			free(xtlv);
> > > > > > 			return -EFAULT;
> > > > > > 		}
> > > > > > 		memcpy(tlv, xtlv->tlv, xtlv->tlv[1] + 2 * sizeof(unsigned int));
> > > > > > 
> > > > > > Do you mean somewhere here triggers a crash?
> > > > > 
> > > > > Yes while it tried to memcpy, in my case 30K sized data to 4K buffer, so I
> > > > > allocated right one and got all the data
> > > > 
> > > > But it has the size check before memcpy()?
> > > 
> > > Okay I had some issues (yet again) so I rebuilt the ubuntu packages and tools and reran
> > > this.
> > > 
> > > I get:
> > > 
> > > $ amixer -c0 cget numid=16
> > > numid=16,iface=MIXER,name='mdl params'
> > >   ; type=BYTES,access=-----RW-,values=30336
> > > amixer: Control hw:0 element TLV read error: Bad address
> > > 
> > > Segmentation fault (core dumped)
> > > 
> > > And the alsa-lib returns an err and we try to free up tlv on error which
> > > should be fine here but fails
> > > 
> > > Why should free cause a failure here (on 1.0.27)
> > > 
> > > On latest lib from git. I get same failure but in alsa-lib when it tries to
> > > free xtlv on failure of this check
> > > 
> > > if (xtlv->tlv[1] + 2 * sizeof(unsigned int) > tlv_size) {
> > >                    free(xtlv);
> > > 
> > > Why would that happen...? What am I missing :(
> > 
> > No idea.  You should check it via gdb.
> 
> Yes did, but didn't get a clue. tlv seems to be valid before free and points
> to right location and contents

Could you show the backtrace?


Takashi