xdgmime: Handle buggy type definitions with circular inheritance

This fixes a stack overflow reported by a user who had both the
definition of text/javascript from shared-mime-info 2.3 and the
definition of text/javascript from shared-mime-info 2.4 installed at the
same time. In 2.3, text/javascript is a subtype of
application/ecmascript, but in 2.4 application/ecmascript is a subtype
of text/javascript. Having both at the same time resulted in circular
inheritance.

The new logic keeps a list of all parents that have already been
checked, which is more comprehensive than the old workaround that was
implemented in commit 38869ece2 ("xdgmime: Prevent infinite loops from
badly-formed MIME registrations").

https://bugs.archlinux.org/task/80279

gio/xdgmime/xdgmime.c

@@ -835,13 +835,16 @@ xdg_mime_is_super_type (const char *mime)
 
 int
 _xdg_mime_mime_type_subclass (const char *mime,
-			      const char *base)
+			      const char *base,
+			      const char **seen)
 {
-  const char *umime, *ubase;
+  const char *umime, *ubase, *parent;
   const char **parents;
 
+  int first_seen = 0, i, ret = 0;
+
   if (_caches)
-    return _xdg_mime_cache_mime_type_subclass (mime, base);
+    return _xdg_mime_cache_mime_type_subclass (mime, base, NULL);
 
   umime = _xdg_mime_unalias_mime_type (mime);
   ubase = _xdg_mime_unalias_mime_type (base);
@@ -865,14 +868,38 @@ _xdg_mime_mime_type_subclass (const char *mime,
       strncmp (umime, "inode/", 6) != 0)
     return 1;
 
+  if (!seen)
+    {
+      seen = calloc (1, sizeof (char *));
+      first_seen = 1;
+    }
+
   parents = _xdg_mime_parent_list_lookup (parent_list, umime);
   for (; parents && *parents; parents++)
     {
-      if (_xdg_mime_mime_type_subclass (*parents, ubase))
-	return 1;
+      parent = *parents;
+
+      /* Detect and avoid buggy circular relationships */
+      for (i = 0; seen[i] != NULL; i++)
+        if (parent == seen[i])
+          goto next_parent;
+      seen = realloc (seen, (i + 2) * sizeof (char *));
+      seen[i] = parent;
+      seen[i + 1] = NULL;
+
+      if (_xdg_mime_mime_type_subclass (parent, ubase, seen))
+        {
+          ret = 1;
+          goto done;
         }
 
-  return 0;
+    next_parent:
+    }
+
+done:
+  if (first_seen)
+    free (seen);
+  return ret;
 }
 
 int
@@ -881,7 +908,7 @@ xdg_mime_mime_type_subclass (const char *mime,
 {
   xdg_mime_init ();
 
-  return _xdg_mime_mime_type_subclass (mime, base);
+  return _xdg_mime_mime_type_subclass (mime, base, NULL);
 }
 
 char **

gio/xdgmime/xdgmime.h

@@ -125,7 +125,8 @@ void xdg_mime_set_dirs (const char * const *dirs);
 int          _xdg_mime_mime_type_equal             (const char *mime_a,
 						    const char *mime_b);
 int          _xdg_mime_mime_type_subclass          (const char *mime,
-						    const char *base);
+						    const char *base,
+						    const char **seen);
 const char  *_xdg_mime_unalias_mime_type           (const char *mime);
 
 

gio/xdgmime/xdgmimecache.c

@@ -751,7 +751,7 @@ cache_get_mime_type_for_data (const void *data,
       /* Pick glob-result R where mime_type inherits from R */
       for (n = 0; n < n_mime_types; n++)
         {
-          if (mime_types[n] && _xdg_mime_cache_mime_type_subclass(mime_types[n], mime_type))
+          if (mime_types[n] && _xdg_mime_cache_mime_type_subclass (mime_types[n], mime_type, NULL))
             return mime_types[n];
         }
       if (n == 0)
@@ -901,12 +901,13 @@ is_super_type (const char *mime)
 
 int
 _xdg_mime_cache_mime_type_subclass (const char *mime,
-				    const char *base)
+				    const char *base,
+				    const char **seen)
 {
-  const char *umime, *ubase;
+  const char *umime, *ubase, *parent;
 
   xdg_uint32_t j;
-  int i, min, max, med, cmp;
+  int i, k, min, max, med, cmp, first_seen = 0, ret = 0;
 
   umime = _xdg_mime_cache_unalias_mime_type (mime);
   ubase = _xdg_mime_cache_unalias_mime_type (base);
@@ -933,6 +934,12 @@ _xdg_mime_cache_mime_type_subclass (const char *mime,
       strncmp (umime, "inode/", 6) != 0)
     return 1;
 
+  if (!seen)
+    {
+      seen = calloc (1, sizeof (char *));
+      first_seen = 1;
+    }
+
   for (i = 0; _caches[i]; i++)
     {
       XdgMimeCache *cache = _caches[i];
@@ -966,10 +973,23 @@ _xdg_mime_cache_mime_type_subclass (const char *mime,
 	      for (j = 0; j < n_parents; j++)
 		{
 		  parent_offset = GET_UINT32 (cache->buffer, offset + 4 + 4 * j);
-		  if (strcmp (cache->buffer + parent_offset, mime) != 0 &&
-		      strcmp (cache->buffer + parent_offset, umime) != 0 &&
-		      _xdg_mime_cache_mime_type_subclass (cache->buffer + parent_offset, ubase))
-		    return 1;
+		  parent = cache->buffer + parent_offset;
+
+		  /* Detect and avoid buggy circular relationships */
+		  for (k = 0; seen[k] != NULL; k++)
+		    if (parent == seen[k])
+		      goto next_parent;
+		  seen = realloc (seen, (k + 2) * sizeof (char *));
+		  seen[k] = parent;
+		  seen[k + 1] = NULL;
+
+		  if (_xdg_mime_cache_mime_type_subclass (parent, ubase, seen))
+		    {
+		      ret = 1;
+		      goto done;
+		    }
+
+	        next_parent:
 		}
 
 	      break;
@@ -977,7 +997,10 @@ _xdg_mime_cache_mime_type_subclass (const char *mime,
 	}
     }
 
-  return 0;
+done:
+  if (first_seen)
+    free (seen);
+  return ret;
 }
 
 const char *

gio/xdgmime/xdgmimecache.h

@@ -70,7 +70,8 @@ int          _xdg_mime_cache_mime_type_equal              (const char *mime_a,
 int          _xdg_mime_cache_media_type_equal             (const char *mime_a,
 							   const char *mime_b);
 int          _xdg_mime_cache_mime_type_subclass           (const char *mime_a,
-							   const char *mime_b);
+							   const char *mime_b,
+							   const char **seen);
 char       **_xdg_mime_cache_list_mime_parents		  (const char *mime);
 const char  *_xdg_mime_cache_unalias_mime_type            (const char *mime);
 int          _xdg_mime_cache_get_max_buffer_extents       (void);