1 files changed, 38 insertions, 0 deletions
diff --git a/debian/patches/0071-video-readers-png-Avoid-heap-OOB-R-W-inserting-huff-.patch b/debian/patches/0071-video-readers-png-Avoid-heap-OOB-R-W-inserting-huff-.patch
new file mode 100644
index 0000000..7f73935
--- /dev/null
+++ b/debian/patches/0071-video-readers-png-Avoid-heap-OOB-R-W-inserting-huff-.patch
@@ -0,0 +1,38 @@
+From 21e3b255f91d9b7711f8346f1e4acf8cc19bf4fb Mon Sep 17 00:00:00 2001
+From: Daniel Axtens <dja@axtens.net>
+Date: Tue, 6 Jul 2021 23:25:07 +1000
+Subject: video/readers/png: Avoid heap OOB R/W inserting huff table items
+
+In fuzzing we observed crashes where a code would attempt to be inserted
+into a huffman table before the start, leading to a set of heap OOB reads
+and writes as table entries with negative indices were shifted around and
+the new code written in.
+
+Catch the case where we would underflow the array and bail.
+
+Fixes: CVE-2021-3696
+
+Signed-off-by: Daniel Axtens <dja@axtens.net>
+Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
+---
+ grub-core/video/readers/png.c | 7 +++++++
+ 1 file changed, 7 insertions(+)
+
+diff --git a/grub-core/video/readers/png.c b/grub-core/video/readers/png.c
+index a3161e25b..d7ed5aa6c 100644
+--- a/grub-core/video/readers/png.c
++++ b/grub-core/video/readers/png.c
+@@ -438,6 +438,13 @@ grub_png_insert_huff_item (struct huff_table *ht, int code, int len)
+   for (i = len; i < ht->max_length; i++)
+     n += ht->maxval[i];
+ 
++  if (n > ht->num_values)
++    {
++      grub_error (GRUB_ERR_BAD_FILE_TYPE,
++		  "png: out of range inserting huffman table item");
++      return;
++    }
++
+   for (i = 0; i < n; i++)
+     ht->values[ht->num_values - i] = ht->values[ht->num_values - i - 1];
+