[mythtv] lirc_client.c sending empty CODE cmd to LIRC -> segfault

David Kubicek foceni at gmail.com
Tue Feb 9 22:42:49 UTC 2010

On 02/09/2010 10:09 PM, Michael T. Dean wrote:
> On 02/09/2010 03:42 PM, David Kubicek wrote:
>> Hello,
>> I was just playing with the optional lircrcd LIRC daemon and it kept
>> segfaulting on me. I found the bug in the daemon (latest CVS version),
>> but the reason for this is MythTV sending an empty CODE command. Until
>> the bug is fixed in either of these two applications, it'll break
>> advanced LIRC configurations...
>> I haven't looked into MythTV, so I have no patch for you, but I'll be
>> sending a patch to LIRC people. If you actually want the patch and it
>> would be integrated soon (e.i. not in 6 months:)) Well, the command
>> packet is actually from lircd, but it really originates in MythTV.
>> LOG:
>> lircrcd[3673]: received command: "CODE 01007f0000000000 1e Down
>> imon_ultrabay_pad"
>> ...
>> lircrcd[3673]: received command: "CODE 01007f0000000000 22 Down
>> imon_ultrabay_pad"
>> ...
>> lircrcd[3673]: received command: "CODE "
>> Segfault in lircrcd (not relevant for you):
>> #0 0xb764af93 in strlen () from /lib/tls/i686/cmov/libc.so.6
>> #1 0xb764acd5 in strdup () from /lib/tls/i686/cmov/libc.so.6
>> #2 0x0804a121 in code_func (fd=-1217294348, message=0x0,
>> arguments=0x0) at lircrcd.c:489
>> #3 0x0804adbd in get_command (argc=2, argv=0xbfe70a04) at lircrcd.c:646
>> #4 loop (argc=2, argv=0xbfe70a04) at lircrcd.c:737
>> #5 main (argc=2, argv=0xbfe70a04) at lircrcd.c:1010
> Are you sure it's not: http://svn.mythtv.org/trac/ticket/7653 ? Can you
> test that patch and provide feedback on it?
> Also, can you get a fix into lircrcd to accept line feeds properly (you
> mentioned you're already planning to send a patch to the LIRC devs for
> something else)?

That's right, the patch is finished and I'm going to notify LIRC people 
tomorrow. I know about #7653 (found it via google), first I made the 
change (added '\n'), but problem persisted.

LIRC CVS checkout and gdb revealed a NULL dereference bug. The CODE 
handler didn't have a NULL check after strtok() (message 'CODE ' 
triggers it). The remaining command handlers are OK. So yes, this is new 
and in both applications. In MythTV I can trigger 'CODE ' easily by 
push-repeat of directional movement, like scrolling down the list. Fast 
repeat rate possibly required. Sometimes it happens instantly, sometimes 
I have to jiggle a few other buttons around and keep scrolling up and 
down for a while.

As for #7652, not including '\n' after CODE cmd is a protocol violation 
to which lircrcd apparently react by exit. Either they consider "lost 
sync" critical or it's just not handled very gracefully. So there is no 
segfault in that case, just controlled shutdown. It's still present in 
CVS and #7652 really should be fixed. After all, it's just adding a '\n' 
at the end of one string in libmythui/lirc_client.c...

See you,

David Kubicek

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