Re: [PATCH] credential: treat "?" and "#" in URLs as end of host

[Taylor Blau <me@ttaylorr.com>]

Hi Peff,

On Tue, Apr 14, 2020 at 05:43:04PM -0400, Jeff King wrote:
> It's unusual to see:
>
>   https://example.com?query-parameters
>
> without an intervening slash, like:
>
>   https://example.com/some-path?query-parameters
>
> or even:
>
>   https://example.com/?query-parameters
>
> but it is a valid end to the hostname (actually "authority component")
> according to RFC 3986. Likewise for "#".
>
> And curl will parse the URL according to the standard, meaning it will
> contact example.com, but our credential code would ask about a bogus
> hostname with a "?" in it. Let's make sure we follow the standard, and
> more importantly ask about the same hosts that curl will be talking to.
>
> It would be nice if we could just ask curl to parse the URL for us. But
> it didn't grow a URL-parsing API until 7.62, so we'd be stuck with
> fallback code either way. Plus we'd need this code in the main Git
> binary, where we've tried to avoid having a link dependency on libcurl.
>
> But let's at least fix our parser. Moving to curl's parser would prevent
> other potential discrepancies, but this gives us immediate relief for
> the known problem, and would help our fallback code if we eventually use
> curl.
>
> Signed-off-by: Jeff King <peff@peff.net>

All makes sense to me. I agree that it would probably be preferable if
we could just use cURL's own parser and forget about this code entirely.
But, having it still be a fallback knocks out any benefit that we'd be
getting by relying on their parser rather than our own.

> ---
> Just a follow-on to today's release. This isn't security critical after
> the earlier fix, but it made some of the attack vectors much easier.

Yep, thanks for noting.

>  credential.c           |  9 ++++++++-
>  t/t0300-credentials.sh | 36 +++++++++++++++++++++++++++++++++++-
>  2 files changed, 43 insertions(+), 2 deletions(-)
>
> diff --git a/credential.c b/credential.c
> index 21b3ba152f..8aa9777548 100644
> --- a/credential.c
> +++ b/credential.c
> @@ -388,7 +388,14 @@ int credential_from_url_gently(struct credential *c, const char *url,
>  	cp = proto_end + 3;
>  	at = strchr(cp, '@');
>  	colon = strchr(cp, ':');
> -	slash = strchrnul(cp, '/');
> +
> +	/*
> +	 * A query or fragment marker before the slash ends the host portion.
> +	 * We'll just continue to call this "slash" for simplicity. Notably our
> +	 * "trim leading slashes" part won't skip over this part of the path,
> +	 * but that's what we'd want.
> +	 */
> +	slash = cp + strcspn(cp, "/?#");
>
>  	if (!at || slash <= at) {
>  		/* Case (1) */
> diff --git a/t/t0300-credentials.sh b/t/t0300-credentials.sh
> index 5b78ebbc3f..b6ec676989 100755
> --- a/t/t0300-credentials.sh
> +++ b/t/t0300-credentials.sh
> @@ -443,11 +443,45 @@ test_expect_success 'url parser ignores embedded newlines' '
>  	username=askpass-username
>  	password=askpass-password
>  	--
> -	warning: url contains a newline in its host component: https://one.example.com?%0ahost=two.example.com/
> +	warning: url contains a newline in its path component: https://one.example.com?%0ahost=two.example.com/
>  	warning: skipping credential lookup for url: https://one.example.com?%0ahost=two.example.com/
>  	askpass: Username:
>  	askpass: Password:
>  	EOF
>  '
>
> +# usage: check_host_and_path <url> <expected-host> <expected-path>
> +check_host_and_path () {
> +	# we always parse the path component, but we need this to make sure it
> +	# is passed to the helper
> +	test_config credential.useHTTPPath true &&
> +	check fill "verbatim user pass" <<-EOF
> +	url=$1
> +	--
> +	protocol=https
> +	host=$2
> +	path=$3
> +	username=user
> +	password=pass
> +	--
> +	verbatim: get
> +	verbatim: protocol=https
> +	verbatim: host=$2
> +	verbatim: path=$3
> +	EOF
> +}
> +
> +test_expect_success 'url parser handles bare query marker' '
> +	check_host_and_path https://example.com?foo.git example.com ?foo.git
> +'
> +
> +test_expect_success 'url parser handles bare fragment marker' '
> +	check_host_and_path https://example.com#foo.git example.com "#foo.git"
> +'
> +
> +test_expect_success 'url parser not confused by encoded markers' '
> +	check_host_and_path https://example.com%23%3f%2f/foo.git \
> +		"example.com#?/" foo.git
> +'
> +
>  test_done

These look good, too. Thanks for working on this.

> --
> 2.26.1.429.g609150846d

Thanks,
Taylor