Tests: Add a test file for lzma_index_append() integer overflow bug.

This test fails before commit 18d7facd38.

test_files.sh now runs xz -l for bad-3-index-uncomp-overflow.xz
because only then the previously-buggy code path gets tested.
Normal decompression doesn't use lzma_index_append() at all.
Instead, lzma_index_hash functions are used and those already
did the overflow check.

tests/files/README

@@ -209,6 +209,16 @@
     file gets rejected specifically due to Unpadded Size having an invalid
     value.
 
+    bad-3-index-uncomp-overflow.xz has Index whose Uncompressed Size
+    fields have huge values whose sum exceeds the maximum allowed size
+    of 2^63 - 1 bytes. In this file the sum is exactly 2^64.
+    lzma_index_append() in liblzma <= 5.2.6 lacks the integer overflow
+    check for the uncompressed size and thus doesn't catch the error
+    when decoding the Index field in this file. This makes "xz -l"
+    not detect the error and will display 0 as the uncompressed size.
+    Note that regular decompression isn't affected by this bug because
+    it uses lzma_index_hash_append() instead.
+
     bad-2-compressed_data_padding.xz has non-null byte in the padding of
     the Compressed Data field of the first Block.
 

tests/test_files.sh

@@ -53,6 +53,14 @@ do
 	fi
 done
 
+# Testing for the lzma_index_append() bug in <= 5.2.6 needs "xz -l":
+I="$srcdir/files/bad-3-index-uncomp-overflow.xz"
+if test -n "$XZ" && "$XZ" -l "$I" > /dev/null 2>&1; then
+	echo "Bad file succeeded with xz -l: $I"
+	(exit 1)
+	exit 1
+fi
+
 for I in "$srcdir"/files/good-*.lzma
 do
 	if test -z "$XZ" || "$XZ" -dc "$I" > /dev/null; then