Re: Videotext application crashes the kernel due to DVB-demux patch

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Am Montag, den 01.02.2010, 21:00 -0500 schrieb Andy Walls:
> On Mon, 2010-02-01 at 07:41 -0500, Andy Walls wrote:
> > On Mon, 2010-02-01 at 10:56 +0100, Chicken Shack wrote:
> > > Hi,
> > > 
> > > here is a link to a patch which breaks backwards compatibility for a
> > > teletext software called alevt-dvb.
> > > 
> > > http://www.mail-archive.com/linuxtv-commits@xxxxxxxxxxx/msg04638.html
> > > 
> > > The kernel patch was introduced with kernel 2.6.32-rc1.
> > > It was Signed-off-by Brandon Philips, Mauro Carvalho Chehab and its
> > > author, Andreas Oberritter.
> > > 
> 
> > > Regards
> > > 
> > > CS
> > > 
> > > P. S.: This is how the kernel crash looks like:
> > 
> > The information below can get me started.  Could you please provide
> > whole Ooops from the output dmesg or from your /var/log/messages file?
> > 
> > I'll try to look at this tonight.
> > 
> > Regards,
> > Andy
> > 
> > > brian:~# alevt
> > > alevt: SDT: service_id 0xcf24 not in PAT
> > > 
> > > sid:pmtpid:ttpid:type:provider:name:language:texttype:magazine:page
> > > 
> > > 28006:100:130:1:ZDFvision:ZDF:lang=deu:type=1:magazine=1:page=  0
> > > 28011:600:630:1:ZDFvision:ZDFinfokanal:lang=deu:type=1:magazine=1:page=
> > > 0
> > > 28014:650:630:1:ZDFvision:zdf_neo:lang=deu:type=1:magazine=1:page=  0
> > > 28016:1100:630:1:ZDFvision:ZDFtheaterkanal:lang=deu:type=1:magazine=1:page=  0
> > > 28007:200:230:1:ZDFvision:3sat:lang=deu:type=1:magazine=1:page=  0
> > > 28008:300:330:1:ZDFvision:KiKa:lang=deu:type=1:magazine=1:page=  0
> > > 28017:411:8191:2:ZDFvision:DRadio Wissen:lang=:type=0:magazine=0:page=
> > > 0
> > > 28012:700:8191:2:ZDFvision:DKULTUR:lang=:type=0:magazine=0:page=  0
> > > 28013:800:8191:2:ZDFvision:DLF:lang=:type=0:magazine=0:page=  0
> > > 
> > > Using: Service ID = 28006 ; PMT PID = 100 ; TXT PID = 130 ;
> > > Service type = 1 ; Provider Name = ZDFvision ; Service name = ZDF ;
> > > language = deu ; Text type = 1 ; Text Magazine = 1 ; Text page =   0
> > > alevt: ioctl: DMX_SET_PES_FILTER Invalid argument (22)
> > > Getötet
> > > brian:~# 
> > > Message from syslogd@brian at Jan 31 19:52:33 ...
> > >  kernel:[  116.563487] Oops: 0000 [#1] PREEMPT SMP 
> > > 
> > > Message from syslogd@brian at Jan 31 19:52:33 ...
> > >  kernel:[  116.563492] last sysfs
> > > file: /sys/devices/pci0000:00/0000:00:1d.7/usb1/1-0:1.0/uevent
> > > 
> > > Message from syslogd@brian at Jan 31 19:52:33 ...
> > >  kernel:[  116.563589] Process alevt (pid: 1780, ti=e7934000
> > > task=e7915be0 task.ti=e7934000)
> > > 
> > > Message from syslogd@brian at Jan 31 19:52:33 ...
> > >  kernel:[  116.563592] Stack:
> > > 
> > > Message from syslogd@brian at Jan 31 19:52:33 ...
> > >  kernel:[  116.563622] Call Trace:
> > > 
> > > Message from syslogd@brian at Jan 31 19:52:33 ...
> > >  kernel:[  116.563650] Code: f2 da 4c c8 8d 56 78 89 54 24 04 89 d0 e8
> > > e4 da 4c c8 89 f0 e8 31 ff ff ff 83 7e 4c 01 76 73 83 7e 48 02 75 49 8b
> > > 46 04 8d 48 f8 <8b> 41 08 8d 58 f8 8d 7e 04 eb 28 8b 41 08 8b 51 0c 89
> > > 50 04 89 
> 
> > > Message from syslogd@brian at Jan 31 19:52:33 ...
> > >  kernel:[  116.563697] EIP: [<f8cec1b2>] dvb_demux_release+0x43/0x183
> > > [dvb_core] SS:ESP 0068:e7935f58
> > > 
> > > Message from syslogd@brian at Jan 31 19:52:33 ...
> > >  kernel:[  116.563706] CR2: 0000000000000000
> 
> I don't have a 32 bti machine set up to compile the module and compare
> the disassembly directly.  However, the kernel code above disassembles
> to this, and is supposedly in dvb_demux_release() but things have been
> inlined by the compiler:
> 
>   1c:	8d 56 78             	lea    0x78(%esi),%edx
>   1f:	89 54 24 04          	mov    %edx,0x4(%esp)
>   23:	89 d0                	mov    %edx,%eax
>   25:	e8 e4 da 4c c8       	call   0xc84cdb0e
>   2a:	89 f0                	mov    %esi,%eax
>   2c:	e8 31 ff ff ff       	call   0xffffff62
> 					(dmxdev.c:dvb_dmxdev_filter_reset() appears to be inlined starting here
> 					 %esi holds dmxdevfilter)
>   31:	83 7e 4c 01          	cmpl   $0x1,0x4c(%esi)    if (dmxdevfilter->state < DMXDEV_STATE_SET)
>   35:	76 73                	jbe    0xaa               	return 0;
>   37:	83 7e 48 02          	cmpl   $0x2,0x48(%esi)    if (dmxdevfilter->type == DMXDEV_TYPE_PES)
>   3b:	75 49                	jne    0x86
> 					(dvb_dmxdev_delete_pids() appears to be inlined starting here
> 					 %esi still holds dmxdevfilter)
>   3d:	8b 46 04             	mov    0x4(%esi),%eax     %eax gets loaded with &dmxdevfilter->feed.ts  for list_for_each_entry_safe(feed, tmp, &dmxdevfilter->feed.ts, ...
>   40:	8d 48 f8             	lea    -0x8(%eax),%ecx    %ecx is "feed" and gets loaded with the next struct dmxdev_feed pointed to by the &dmxdevfilter->feed.ts list
>   43:	8b 41 08             	mov    0x8(%ecx),%eax     Oops appears to happen here: %ecx and hence "feed" was (craftily?) set to 0xfffffff8 based on CR2 above
>   46:	8d 58 f8             	lea    -0x8(%eax),%ebx
>   49:	8d 7e 04             	lea    0x4(%esi),%edi
>   4c:	eb 28                	jmp    0x76
>   4e:	8b 41 08             	mov    0x8(%ecx),%eax
>   51:	8b 51 0c             	mov    0xc(%ecx),%edx
>   54:	89 50 04             	mov    %edx,0x4(%eax)
> 
> 
> So there is something wrong with the list manipulations or, if needed,
> locking around the the list manipulations of the list that was
> introduced in the patch you identified as the problem.  That is what is
> causing the Ooops on close().  It will take a some more scrutiny to see
> what exactly is wrong.
> 
> 
> There also may be another different problem.  I note that alevt outputs
> this perror() message:
> 
> 	alevt: ioctl: DMX_SET_PES_FILTER Invalid argument (22)

> There may possibly have been an unintended change in ioctl() semantics
> with the patch.  I have not investigated this at all yet.


Voila!

This is the context of the perror message:

a. this is the title of the function:

static int vbi_dvb_open(struct vbi *vbi, const char *vbi_name,
	const char *channel, char *outfile, u_int16_t sid, int ttpid)

b. and this is the immediate context of the perror message:

	memset(&filterpar, 0, sizeof(filterpar));
	filterpar.pid = vbi->ttpid;
        filterpar.input = DMX_IN_FRONTEND;
        filterpar.output = DMX_OUT_TAP;
        filterpar.pes_type = DMX_PES_OTHER;
        filterpar.flags = DMX_IMMEDIATE_START;
        if (ioctl(vbi->fd, DMX_SET_PES_FILTER, &filterpar) < 0) {
        error("ioctl: DMX_SET_PES_FILTER %s (%u)", strerror(errno),
errno);
        goto outerr;
        }
	return 0;

 outerr:
	close(vbi->fd);
	vbi->fd = -1;
	return -1;
}

If you compare that to other teletext applications you will easily find
out that there is absolutely nothing irregular about it: all standard
calls, free from bugs or syntax errors.

So the incriminated patch (see Internet link above) is something like a
trojan horse, a virus. It is definitely not a valid extension of the DVB
demux device.

a. What is the "Invalid argument"?
b. And what does "22" mean?

The answers lie in the incriminated kernel patch (see Internet link
above), but definitely NOT in the application (alevt-dvb).

Thanks for your engagement, Andy!
It's a golden donation to have people like you around!

I really wonder for what three valid signatures (i. e. Signed-off-by)
are here for if the people in question obviously do not know, comprehend
or understand what they are doing!

Under normal conditions the intention of more than one signature is a
kind of control function. But how can one execute control over a kernel
changeset if the profound competence is missing??


> That's all I have time for tonight.  The soonest I will be able to give
> more attention to this is on Wednesday evening.
> 
> Regards,
> Andy
> 
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Regards

CS


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