attr: fix segfault in gitattributes parsing code

git may segfault if gitattributes contains an invalid
entry. A test is added to t0020 that triggers the segfault.
The parsing code is fixed to avoid the crash.

Signed-off-by: Steffen Prohaska <prohaska@zib.de>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

1 files changed, 4 insertions, 1 deletions

diff --git a/attr.c b/attr.c
index 129399310a..6e82507be7 100644
--- a/attr.c
+++ b/attr.c
@@ -214,8 +214,11 @@ static struct match_attr *parse_attr_line(const char *line, const char *src,
 		num_attr = 0;
 		cp = name + namelen;
 		cp = cp + strspn(cp, blank);
-		while (*cp)
+		while (*cp) {
 			cp = parse_attr(src, lineno, cp, &num_attr, res);
+			if (!cp)
+				return NULL;
+		}
 		if (pass)
 			break;
 		res = xcalloc(1,