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

From: René Scharfe <l.s.r@web.de>
Date: Jun 4, 2019, 05:00 UTC
Message-ID: <18ab56e2-3b25-8cfd-438d-72f49145adc4@web.de>
In-Reply-To: <20190603204526.7723-2-matvore@google.com>

Am 03.06.19 um 22:45 schrieb Matthew DeVore:

Show 28 quoted lines

> 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.
>
> 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..c0bb4e23c3 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 >= 3) {

Tricky. hex2chr() makes sure to not run over the end of NUL-terminated strings, but url_decode_internal() is supposed to honor the parameter len as well. Your change disables %-decoding for the two callers that pass -1 as len, though. So perhaps like this?

		if (c == '%' && (len < 0 || len >= 3)) {

In any case: Good find!

Show 11 quoted lines

>  			int val = hex2chr(q + 1);
>  			if (0 <= val) {
>  				strbuf_addch(out, val);
>  				q += 3;
>  				len -= 3;
>  				continue;
>  			}
>  		}
>
>  		if (decode_plus && c == '+')
>