From Dirk: fix https://bugs.wireshark.org/bugzilla/show_bug.cgi?id=2930 :

Make the image (png, gif, jfif) dissectors "new style" so that they don't
dissect data that does not belong to them.

Modify the HTTP dissector to call heuristic dissectors on the body if the
registered subdissector does not accept/dissect the data.

From me: don't use assert() and don't add a preference to the HTTP dissector
for this behavior: it makes sense to behave like that by default.


git-svn-id: http://anonsvn.wireshark.org/wireshark/trunk@36305 f5534014-38df-0310-8fa8-9805f1628bb7

1 files changed, 20 insertions, 45 deletions

diff --git a/epan/dissectors/packet-image-gif.c b/epan/dissectors/packet-image-gif.c
index ae1c5d3daa..7ee60945b6 100644
--- a/epan/dissectors/packet-image-gif.c
+++ b/epan/dissectors/packet-image-gif.c
@@ -13,21 +13,21 @@
  * Copyright 1998 Gerald Combs
  *
  * Compuserve GIF media decoding functionality provided by Olivier Biot.
- * 
+ *
  * The two GIF specifications are found at several locations, such as W3C:
  * http://www.w3.org/Graphics/GIF/spec-gif87.txt
  * http://www.w3.org/Graphics/GIF/spec-gif89a.txt
- * 
+ *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License
  * as published by the Free Software Foundation; either version 2
  * of the License, or (at your option) any later version.
- * 
+ *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
- * 
+ *
  * You should have received a copy of the GNU General Public License
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
@@ -80,7 +80,6 @@ static const value_string vals_extensions[] = {
 };
 
 enum {
-	GIF_UNKNOWN = 0,
 	GIF_87a = 0x87,
 	GIF_89a = 0x89,
 };
@@ -130,19 +129,6 @@ static gint ett_extension = -1;
 static gint ett_image = -1;
 
 
-/**************** GIF related declarations and definitions ****************/
-
-
-/************************** Function prototypes **************************/
-
-
-static void
-dissect_gif(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree);
-
-void
-proto_register_gif(void);
-
-
 /****************** GIF protocol dissection functions ******************/
 
 /* There are two Compuserve GIF standards: GIF87a and GIF89a. GIF image files
@@ -150,7 +136,7 @@ proto_register_gif(void);
  * string representation of the version: "GIF87a" or "GIF89a".
  */
 
-static void
+static gint
 dissect_gif(tvbuff_t *tvb, packet_info *pinfo _U_, proto_tree *tree)
 {
 	proto_item *ti;
@@ -163,19 +149,24 @@ dissect_gif(tvbuff_t *tvb, packet_info *pinfo _U_, proto_tree *tree)
 	guint8 image_bpp;
 	guint tvb_len = tvb_reported_length(tvb);
 	char *str = tvb_get_ephemeral_string(tvb, 0, 6);
-	guint8 version;
+	guint8 version = 0;
+
+	if (tvb_len < 20)
+		return 0;
 
 	/* Check whether we're processing a GIF object */
+	/* see http://www.w3.org/Graphics/GIF/spec-gif89a.txt section 17 */
 	if (strcmp(str, "GIF87a") == 0) {
 		version = GIF_87a;
 	} else if (strcmp(str, "GIF89a") == 0) {
 		version = GIF_89a;
-	} else if (strncmp(str,"GIF", 3) == 0) {
-		version = GIF_UNKNOWN;
 	} else {
 		/* Not a GIF image! */
-		return;
+		return 0;
 	}
+
+	DISSECTOR_ASSERT(version);
+
 	/* Add summary to INFO column if it is enabled */
 	if (check_col(pinfo->cinfo, COL_INFO))
 		col_append_fstr(pinfo->cinfo, COL_INFO, " (%s)", str);
@@ -191,9 +182,6 @@ dissect_gif(tvbuff_t *tvb, packet_info *pinfo _U_, proto_tree *tree)
 		gif_tree = proto_item_add_subtree(ti, ett_gif);
 		/* GIF signature */
 		ti = proto_tree_add_item(gif_tree, hf_version, tvb, 0, 6, TRUE);
-		if (version == GIF_UNKNOWN) {
-			proto_item_append_text(ti, " <Error: unknown GIF version>");
-		}
 		/* Screen descriptor */
 		proto_tree_add_item(gif_tree, hf_screen_width, tvb, 6, 2, TRUE);
 		proto_tree_add_item(gif_tree, hf_screen_height, tvb, 8, 2, TRUE);
@@ -209,7 +197,7 @@ dissect_gif(tvbuff_t *tvb, packet_info *pinfo _U_, proto_tree *tree)
 		color_map_present = peek & 0x80;
 		color_resolution = 1 + ((peek & 0x60) >> 4);
 		image_bpp = 1 + (peek & 0x07);
-	
+
 		ti = proto_tree_add_text(gif_tree, tvb, 10, 1,
 				"Global settings:");
 		if (color_map_present)
@@ -374,7 +362,7 @@ dissect_gif(tvbuff_t *tvb, packet_info *pinfo _U_, proto_tree *tree)
 				color_map_present = peek & 0x80;
 				color_resolution = 1 + ((peek & 0x60) >> 4);
 				image_bpp = 1 + (peek & 0x07);
-	
+
 				ti2 = proto_tree_add_text(subtree, tvb, offset, 1,
 						"Local settings:");
 				if (color_map_present)
@@ -431,23 +419,13 @@ dissect_gif(tvbuff_t *tvb, packet_info *pinfo _U_, proto_tree *tree)
 			}
 		} /* while */
 	}
+	return offset;
 }
 
 static gboolean
 dissect_gif_heur(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
 {
-	if (tvb_length(tvb) < 20)
-		return FALSE;
-
-	/* see http://www.w3.org/Graphics/GIF/spec-gif89a.txt section 17 */
-	if ((tvb_strneql(tvb, 0, "GIF89a", 6) == 0) ||
-	    (tvb_strneql(tvb, 0, "GIF87a", 6) == 0))
-	{
-		dissect_gif(tvb, pinfo, tree);
-		return TRUE;
-	}
-
-	return FALSE;
+	return dissect_gif(tvb, pinfo, tree) > 0;
 }
 
 
@@ -701,17 +679,14 @@ proto_register_gif(void)
 	proto_register_field_array(proto_gif, hf, array_length(hf));
 	proto_register_subtree_array(ett, array_length(ett));
 
-	register_dissector(IMG_GIF, dissect_gif, proto_gif);
+	new_register_dissector(IMG_GIF, dissect_gif, proto_gif);
 }
 
 
 void
 proto_reg_handoff_gif(void)
 {
-	dissector_handle_t gif_handle;
-
-	gif_handle = find_dissector(IMG_GIF);
-
+	dissector_handle_t gif_handle = find_dissector(IMG_GIF);
 	/* Register the GIF media type */
 	dissector_add_string("media_type", "image/gif", gif_handle);
 	heur_dissector_add("http", dissect_gif_heur, proto_gif);