[PATCH v2 1/2] url: do not read past end of buffer

[Matthew DeVore <matvore@google.com>]

url_decode_internal could have been tricked into reading past the length
of the **query buffer if there are fewer than 2 characters after a % (in
a null-terminated string, % would have to be the last character).
Prevent this from happening by checking len before decoding the %
sequence.

Helped-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Matthew DeVore <matvore@google.com>
---
 url.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/url.c b/url.c
index 25576c390b..9ea9d5611b 100644
--- a/url.c
+++ b/url.c
@@ -39,21 +39,21 @@ static char *url_decode_internal(const char **query, int len,
 		unsigned char c = *q;
 
 		if (!c)
 			break;
 		if (stop_at && strchr(stop_at, c)) {
 			q++;
 			len--;
 			break;
 		}
 
-		if (c == '%') {
+		if (c == '%' && (len < 0 || len >= 3)) {
 			int val = hex2chr(q + 1);
 			if (0 <= val) {
 				strbuf_addch(out, val);
 				q += 3;
 				len -= 3;
 				continue;
 			}
 		}
 
 		if (decode_plus && c == '+')
-- 
2.21.0