[vlc-devel] [PATCH] playlist service discovery NULL pointer dereference

[Alexander Gall]

This code assumes that the "name" and "category" fields of a sd item
are always set.  VLC crashes immediately if SAP is turned on in a
network that has global multicast connectivity.  Apparently, most
session descriptions sent to the global SAP group are missing the
field that is interpreted as "category" (I didn't bother to track down
which field that is) and some are also missing the one from which the
"name" is derived.  I don't know whether those fields are mandatory or
not in the session descriptions and it doesn't really matter.  VLC
should just do something sensible instead of crashing.

I'd like to make a general comment on the handling of strings in VLC.
Many of the bugs I stumble upon when building VLC from the svn trunk
are of this kind.  There must be loads and loads more of them.  Maybe
it would be a good idea to practice some "defensive programming" and
check those pointers before using them.  That would avoid many of the
crashes (when a NULL pointer is not really a problem like in this
case) or would at least lead to a crash with better diagnostics when
an inconsistency is fatal.

-- 
Alex

--- src/playlist/services_discovery.c.orig      2007-08-20 17:22:38.342472000 +0200
+++ src/playlist/services_discovery.c   2007-08-20 17:15:18.885875000 +0200
@@ -183,7 +183,9 @@
     const char * psz_cat = p_event->u.services_discovery_item_added.psz_category;
     playlist_item_t *p_new_item, * p_parent = user_data;
 
-    msg_Dbg( p_parent->p_playlist, "Adding %s in %s", p_input->psz_name, psz_cat );
+    msg_Dbg( p_parent->p_playlist, "Adding %s in %s", 
+            p_input->psz_name ? p_input->psz_name : "<UNKNOWN>", 
+            psz_cat ? psz_cat : "<UNKNOWN>");
 
     /* If p_parent is in root category (this is clearly a hack) and we have a cat */
     if( !EMPTY_STR(psz_cat) &&

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