mpeg: handle the presence of an image in the ID3v2 header.

Fixes #17985.

wiretap/mpeg.c

@@ -163,7 +163,22 @@ mpeg_read_packet(wtap *wth, FILE_T fh, wtap_rec *rec, Buffer *buf,
 				}
 			}
 		} else {
-			packet_size = mpeg_resync(fh, err);
+			if ((n & 0xffffff00) == 0x49443300) {
+				/* We have an ID3v2 header; read the size */
+				if (file_seek(fh, 6, SEEK_CUR, err) == -1)
+					return FALSE;
+				if (!wtap_read_bytes_or_eof(fh, &n, sizeof n, err, err_info))
+					return FALSE;
+				if (file_seek(fh, -(gint64)(6+sizeof(n)), SEEK_CUR, err) == -1)
+					return FALSE;
+				n = g_ntohl(n);
+
+				/* ID3v2 size does not include the 10-byte header */
+				packet_size = decode_synchsafe_int(n) + 10;
+			} else {
+				packet_size = mpeg_resync(fh, err);
+			}
+
 			if (packet_size == 0)
 				return FALSE;
 		}

wsutil/mpeg-audio.c

@@ -81,6 +81,33 @@ mpa_padding(const struct mpa *mpa)
 	return(mpa->padding ? mpa_padding_data[mpa_layers[mpa->layer]] : 0);
 }
 
+/* Decode an ID3v2 synchsafe integer.
+ * See https://id3.org/id3v2.4.0-structure section 6.2.
+ */
+guint32
+decode_synchsafe_int(guint32 input)
+{
+	guint32 value;
+
+	/* High-order byte */
+	value = (input >> 24) & 0x7f;
+	/* Shift the result left to make room for the next 7 bits */
+	value <<= 7;
+
+	/* Now OR in the 2nd byte */
+	value |= (input >> 16) & 0x7f;
+	value <<= 7;
+
+	/* ... and the 3rd */
+	value |= (input >> 8) & 0x7f;
+	value <<= 7;
+
+	/* For the 4th byte don't do the shift */
+	value |= input & 0x7f;
+
+	return value;
+}
+
 /*
  * Editor modelines  -  https://www.wireshark.org/tools/modelines.html
  *

wsutil/mpeg-audio.h

@@ -11,6 +11,7 @@
 #ifndef MPA_H
 #define MPA_H 1
 
+#include <glib.h>
 #include "ws_symbol_export.h"
 
 struct mpa {
@@ -71,6 +72,8 @@ WS_DLL_PUBLIC
 unsigned int mpa_frequency(const struct mpa *);
 WS_DLL_PUBLIC
 unsigned int mpa_padding(const struct mpa *);
+WS_DLL_PUBLIC
+guint32 decode_synchsafe_int(guint32);
 
 #define MPA_DATA_BYTES(mpa) (mpa_bitrate(mpa) * mpa_samples(mpa) \
 		/ mpa_frequency(mpa) / 8)