[glib] gcontenttype: Fix a potential NULL pointer dereference

[Philip Withnall <pwithnall src gnome org>]

commit 8b9e8dc53b1efba01d760cde9d2cb01fdee51cf7
Author: Philip Withnall <philip withnall collabora co uk>
Date:   Tue Nov 26 11:12:48 2013 +0000

    gcontenttype: Fix a potential NULL pointer dereference
    
    If the initial part of the header (‘MIME-TreeMagic’) is valid, but the
    following line does not start with ‘[’ (i.e. is not a valid section
    line), insert_matchlet() will be called with a NULL match pointer, and
    will crash with a NULL pointer dereference.
    
    Fix this by bailing out if a valid section line isn’t encountered before
    the first insert_matchlet() call (i.e. between the header line and the
    first data line).
    
    Note that this has not been tested against a real treemagic file; the
    fix is purely theoretical.
    
    Found by scan-build.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=113075

 gio/gcontenttype.c |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletions(-)
---
diff --git a/gio/gcontenttype.c b/gio/gcontenttype.c
index d54f042..8734e7f 100644
--- a/gio/gcontenttype.c
+++ b/gio/gcontenttype.c
@@ -1032,11 +1032,16 @@ read_tree_magic_from_directory (const gchar *prefix)
                   match = parse_header (lines[i]);
                   insert_match (match);
                 }
-              else
+              else if (match != NULL)
                 {
                   matchlet = parse_match_line (lines[i], &depth);
                   insert_matchlet (match, matchlet, depth);
                 }
+              else
+                {
+                  g_warning ("%s: header corrupt; skipping\n", filename);
+                  break;
+                }
             }
 
           g_strfreev (lines);