[mythtv-commits] Ticket #1459: Mythbackend SEGV during EIT scan - svn 9246

[MythTV]

#1459: Mythbackend SEGV during EIT scan - svn 9246
----------------------------------------+-----------------------------------
 Reporter:  mythdev at penyball.cix.co.uk  |       Owner:  danielk
     Type:  defect                      |      Status:  new    
 Priority:  minor                       |   Milestone:  0.20   
Component:  mythtv                      |     Version:  head   
 Severity:  medium                      |  
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 I can't see this logged elsewhere - #1441 (housekeeping SEGV) and #1453
 (recording SEGV) may be relevant but this segv occurs during EIT scan with
 SVN 9246 - it was not present in 8927.

 The failure only seems to occur when the EIT scan hits a channel that is
 either a weak signal or is temporarily 'off air'. (The EIT scan looks at
 channels that have been marked as not visible so apart from turning off
 eit scanning there isn't a workaround.)

 I've attached a gdb.txt and the tail end of the mythbackend logs

 within gdb.txt I've included the gdb p results for *this & *psip - the
 psip values show that the _pesdata/_fullbuffer are corrupt. (annotated
 with [jd] )

 The SEGV is triggered by the psip->TableID() - which is invoking the
 StreamID() in pespacket.h
 {{{
 void ATSCStreamData::DeleteCachedTable(PSIPTable *psip) const
 {
     if (!psip)
         return;

     QMutexLocker locker(&_cache_lock);
     if (_cached_ref_cnt[psip] > 0)
     {
         _cached_slated_for_deletion[psip] = 1;
         return;
     }
     else if (TableID::MGT == psip->TableID())          [jd] Segfault here
 }}}
 This segfaults because _pesdata is out of bounds:
 {{{
 [jd] p *psip
 $1 = {<PESPacket> = {_vptr.PESPacket = 0x409f6410,
     _pesdata = 0x4400a00d <Address 0x4400a00d out of bounds>,
     _fullbuffer = 0x4400a008 <Address 0x4400a008 out of bounds>,
     _psiOffset = 4, _ccLast = 2, _pesdataSize = 188, _allocSize = 3948,
     _badPacket = false}, static PSIP_OFFSET = 8}
 }}}

 I'm just rebuilding with the patch from #1456 - however I won't know if
 its had any effect for several hours because I have to wait for the scan
 to hit an off-air channel.  I've logged this as medium severity because
 the backend is failing without user activity and hence will be undetected
 = missed recordings.

 Apologies - there isn't a patch here - I don't understand whats happening
 yet :)

-- 
Ticket URL: <http://svn.mythtv.org/trac/ticket/1459>
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