wildmatch: avoid undefined behavior

phillipwood · gitster · commit 81b26f8f2891 · 2023-03-20T10:58:53.000-07:00
The code changed in this commit is designed to check if the pattern starts with "**/" or contains "/**/" (see 3a078de (wildmatch: fix "**" special case, 2013-01-01)). Unfortunately when the pattern begins with "**/" `prev_p = p - 2` is evaluated when `p` points to the second "*" and so the subtraction is undefined according to section 6.5.6 of the C standard because the result does not point within the same object as `p`. Fix this by avoiding the subtraction unless it is well defined. Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk> Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/wildmatch.c b/wildmatch.c
@@ -83,12 +83,12 @@ static int dowild(const uchar *p, const uchar *text, unsigned int flags)
 			continue;
 		case '*':
 			if (*++p == '*') {
-				const uchar *prev_p = p - 2;
+				const uchar *prev_p = p;
 				while (*++p == '*') {}
 				if (!(flags & WM_PATHNAME))
 					/* without WM_PATHNAME, '*' == '**' */
 					match_slash = 1;
-				else if ((prev_p < pattern || *prev_p == '/') &&
+				else if ((prev_p - pattern < 2 || *(prev_p - 2) == '/') &&
 				    (*p == '\0' || *p == '/' ||
 				     (p[0] == '\\' && p[1] == '/'))) {
 					/*
