115 lines
4.4 KiB
Diff
115 lines
4.4 KiB
Diff
From 6aa11df549114ebda520dde4cdaea2f9357b2c89 Mon Sep 17 00:00:00 2001
|
|
From: Dan Fandrich <dan@coneharvesters.com>
|
|
Date: Fri, 12 Oct 2018 16:01:45 +0200
|
|
Subject: [PATCH] Improve deep recursion detection in
|
|
exif_data_load_data_content.
|
|
|
|
The existing detection was still vulnerable to pathological cases
|
|
causing DoS by wasting CPU. The new algorithm takes the number of tags
|
|
into account to make it harder to abuse by cases using shallow recursion
|
|
but with a very large number of tags. This improves on commit 5d28011c
|
|
which wasn't sufficient to counter this kind of case.
|
|
|
|
The limitation in the previous fix was discovered by Laurent Delosieres,
|
|
Secunia Research at Flexera (Secunia Advisory SA84652) and is assigned
|
|
the identifier CVE-2018-20030.
|
|
---
|
|
NEWS | 1 +
|
|
libexif/exif-data.c | 45 +++++++++++++++++++++++++++++++++++++--------
|
|
2 files changed, 38 insertions(+), 8 deletions(-)
|
|
|
|
diff --git a/libexif/exif-data.c b/libexif/exif-data.c
|
|
index e35403d..a6f9c94 100644
|
|
--- a/libexif/exif-data.c
|
|
+++ b/libexif/exif-data.c
|
|
@@ -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 *data, ExifIfd ifd,
|
|
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 *data, ExifIfd ifd,
|
|
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;
|