diff: prevent pprint_rename from underrunning input

diff --git a/diff.c b/diff.c
index 9038f190ece061696a3290acf8f1e9951e9d0a6c..d641c2676f357e2901c11f83cff4e7176dd0f544 100644 (file)
--- a/diff.c
+++ b/diff.c
@@ -1151,6 +1151,7 @@ static char *pprint_rename(const char *a, const char *b)
        const char *new = b;
        struct strbuf name = STRBUF_INIT;
        int pfx_length, sfx_length;
+       int pfx_adjust_for_slash;
        int len_a = strlen(a);
        int len_b = strlen(b);
        int a_midlen, b_midlen;
@@ -1177,7 +1178,18 @@ static char *pprint_rename(const char *a, const char *b)
        old = a + len_a;
        new = b + len_b;
        sfx_length = 0;
-       while (a <= old && b <= new && *old == *new) {
+       /*
+        * If there is a common prefix, it must end in a slash.  In
+        * that case we let this loop run 1 into the prefix to see the
+        * same slash.
+        *
+        * If there is no common prefix, we cannot do this as it would
+        * underrun the input strings.
+        */
+       pfx_adjust_for_slash = (pfx_length ? 1 : 0);
+       while (a + pfx_length - pfx_adjust_for_slash <= old &&
+              b + pfx_length - pfx_adjust_for_slash <= new &&
+              *old == *new) {
                if (*old == '/')
                        sfx_length = len_a - (old - a);
                old--;