Fix potential heap buffer corruption due to Strgrow

If Str.length = 5 and area_size = 6, the result of Strgrow is still
area_size = 6. For such case, Strcat_char and Strinsert_char will
overflow one byte.

Bug-Debian: https://github.com/tats/w3m/pull/27 [CVE-2016-9442]
Origin: https://github.com/tats/w3m/pull/27/commits/c95a43dc92695464be11c8a51811aaa9761546e6

1 files changed, 2 insertions, 2 deletions

diff --git a/Str.c b/Str.c
index eff82a4..5287c0f 100644
--- a/Str.c
+++ b/Str.c
@@ -232,8 +232,8 @@ Strgrow(Str x)
 {
     char *old = x->ptr;
     int newlen;
-    newlen = x->length * 6 / 5;
-    if (newlen == x->length)
+    newlen = x->area_size * 6 / 5;
+    if (newlen == x->area_size)
 	newlen += 2;
     x->ptr = GC_MALLOC_ATOMIC(newlen);
     x->area_size = newlen;