--- libexif-0.6.21-bak/libexif/exif-data.c	2019-06-13 21:49:15.711000000 -0400
+++ libexif-0.6.21/libexif/exif-data.c	2019-06-13 23:31:41.672000000 -0400
@@ -35,6 +35,7 @@
 #include <libexif/olympus/exif-mnote-data-olympus.h>
 #include <libexif/pentax/exif-mnote-data-pentax.h>
 
+#include <math.h>
 #include <stdlib.h>
 #include <stdio.h>
 #include <string.h>
@@ -350,6 +351,20 @@ if (data->ifd[(i)]->count) {				\
 	break;						\
 }
 
+/*! Calculate the recursion cost added by one level of IFD loading.
+ *
+ * The work performed is related to the cost in the exponential relation
+ *   work=1.1**cost
+ */
+static unsigned int
+level_cost(unsigned int n)
+{
+    static const double log_1_1 = 0.09531017980432493;
+
+	/* Adding 0.1 protects against the case where n==1 */
+	return ceil(log(n + 0.1)/log_1_1);
+}
+
 /*! Load data for an IFD.
  *
  * \param[in,out] data #ExifData
@@ -357,13 +372,13 @@ if (data->ifd[(i)]->count) {				\
  * \param[in] d pointer to buffer containing raw IFD data
  * \param[in] ds size of raw data in buffer at \c d
  * \param[in] offset offset into buffer at \c d at which IFD starts
- * \param[in] recursion_depth number of times this function has been
- * recursively called without returning
+ * \param[in] recursion_cost factor indicating how expensive this recursive
+ * call could be
  */
 static void
 exif_data_load_data_content (ExifData *data, ExifIfd ifd,
 			     const unsigned char *d,
-			     unsigned int ds, unsigned int offset, unsigned int recursion_depth)
+			     unsigned int ds, unsigned int offset, unsigned int recursion_cost)
 {
 	ExifLong o, thumbnail_offset = 0, thumbnail_length = 0;
 	ExifShort n;
@@ -378,9 +393,20 @@ exif_data_load_data_content (ExifData *d
 	if ((((int)ifd) < 0) || ( ((int)ifd) >= EXIF_IFD_COUNT))
 	  return;
 
-	if (recursion_depth > 30) {
+      	if (recursion_cost > 170) {
+		/*
+		 * recursion_cost is a logarithmic-scale indicator of how expensive this
+		 * recursive call might end up being. It is an indicator of the depth of
+		 * recursion as well as the potential for worst-case future recursive
+		 * calls. Since it's difficult to tell ahead of time how often recursion
+		 * will occur, this assumes the worst by assuming every tag could end up
+		 * causing recursion.
+		 * The value of 170 was chosen to limit typical EXIF structures to a
+		 * recursive depth of about 6, but pathological ones (those with very
+		 * many tags) to only 2.
+		 */ 
 		exif_log (data->priv->log, EXIF_LOG_CODE_CORRUPT_DATA, "ExifData",
-			  "Deep recursion detected!");
+               		  "Deep/expensive recursion detected!"); 
 		return;
 	}
 
@@ -422,15 +448,18 @@ exif_data_load_data_content (ExifData *d
 			switch (tag) {
 			case EXIF_TAG_EXIF_IFD_POINTER:
 				CHECK_REC (EXIF_IFD_EXIF);
-				exif_data_load_data_content (data, EXIF_IFD_EXIF, d, ds, o, recursion_depth + 1);
+				exif_data_load_data_content (data, EXIF_IFD_EXIF, d, ds, o,
+					recursion_cost + level_cost(n));
 				break;
 			case EXIF_TAG_GPS_INFO_IFD_POINTER:
 				CHECK_REC (EXIF_IFD_GPS);
-				exif_data_load_data_content (data, EXIF_IFD_GPS, d, ds, o, recursion_depth + 1);
+				exif_data_load_data_content (data, EXIF_IFD_GPS, d, ds, o,
+					recursion_cost + level_cost(n));
 				break;
 			case EXIF_TAG_INTEROPERABILITY_IFD_POINTER:
 				CHECK_REC (EXIF_IFD_INTEROPERABILITY);
-				exif_data_load_data_content (data, EXIF_IFD_INTEROPERABILITY, d, ds, o, recursion_depth + 1);
+				exif_data_load_data_content (data, EXIF_IFD_INTEROPERABILITY, d, ds, o,
+					recursion_cost + level_cost(n));
 				break;
 			case EXIF_TAG_JPEG_INTERCHANGE_FORMAT:
 				thumbnail_offset = o;
