Fix a buffer read overflow in exif_entry_get_value

While parsing EXIF_TAG_FOCAL_LENGTH it was possible to read 8 bytes past
the end of a heap buffer. This was detected by the OSS Fuzz project.
Patch from Google.

Fixes https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=7344 and
https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=14543

diff --git a/libexif/exif-entry.c b/libexif/exif-entry.c
index 61260d3..a224ac2 100644 (file)
--- a/libexif/exif-entry.c
+++ b/libexif/exif-entry.c
@@ -1040,12 +1040,12 @@ exif_entry_get_value (ExifEntry *e, char *val, unsigned int maxlen)
                d = 0.;
                entry = exif_content_get_entry (
                        e->parent->parent->ifd[EXIF_IFD_0], EXIF_TAG_MAKE);
-               if (entry && entry->data &&
+               if (entry && entry->data && entry->size >= 7 &&
                    !strncmp ((char *)entry->data, "Minolta", 7)) {
                        entry = exif_content_get_entry (
                                        e->parent->parent->ifd[EXIF_IFD_0],
                                        EXIF_TAG_MODEL);
-                       if (entry && entry->data) {
+                       if (entry && entry->data && entry->size >= 8) {
                                if (!strncmp ((char *)entry->data, "DiMAGE 7", 8))
                                        d = 3.9;
                                else if (!strncmp ((char *)entry->data, "DiMAGE 5", 8))