On 12/14, Jeff King wrote:
> On Tue, Dec 13, 2016 at 05:40:37PM -0800, Brandon Williams wrote:
>
> > Add the from_user parameter to the 'is_transport_allowed' function.
> > This allows callers to query if a transport protocol is allowed, given
> > that the caller knows that the protocol is coming from the user (1) or
> > not from the user (0) such as redirects in libcurl. If unknown a -1
> > should be provided which falls back to reading `GIT_PROTOCOL_FROM_USER`
> > to determine if the protocol came from the user.
>
> I think your commit message is upside-down with respect to the purpose
> of the patch. The end goal we want is for http to distinguish between
> protocol restrictions for redirects versus initial requests. The rest is
> an implementation detail. It's definitely still worth discussing that
> implementation detail (though I think your in-code comments may be
> sufficient), but I don't see the rationale discussed here at all.
I'll fix the commit message to better discuss the reasoning behind the
change.
> > Signed-off-by: Brandon Williams <bmwill@xxxxxxxxxx>
> > ---
> > http.c | 14 +++++++-------
> > transport.c | 8 +++++---
> > transport.h | 13 ++++++++++---
> > 3 files changed, 22 insertions(+), 13 deletions(-)
>
> I'm trying to think of a way to test this. I guess the case we are
> covering here is when a server redirects, but the protocol is only
> allowed from the user. So:
>
> diff --git a/t/t5812-proto-disable-http.sh b/t/t5812-proto-disable-http.sh
> index 044cc152f..d911afd24 100755
> --- a/t/t5812-proto-disable-http.sh
> +++ b/t/t5812-proto-disable-http.sh
> @@ -30,5 +30,12 @@ test_expect_success 'curl limits redirects' '
> test_must_fail git clone "$HTTPD_URL/loop-redir/smart/repo.git"
> '
>
> +test_expect_success 'http can be limited to from-user' '
> + git -c protocol.http.allow=user \
> + clone "$HTTPD_URL/smart/repo.git" plain.git &&
> + test_must_fail git -c protocol.http.allow=user \
> + clone "$HTTPD_URL/smart-redir-perm/repo.git" redir.git
> +'
> +
> stop_httpd
> test_done
>
> It's an oddball configuration, and you'd probably just set
> http.followRedirects=false in practice, but it does correctly check this
> case.
K I'll add this in as a test.
> > @@ -588,9 +588,9 @@ static CURL *get_curl_handle(void)
> > #endif
> > #if LIBCURL_VERSION_NUM >= 0x071304
> > curl_easy_setopt(result, CURLOPT_REDIR_PROTOCOLS,
> > - get_curl_allowed_protocols());
> > + get_curl_allowed_protocols(0));
> > curl_easy_setopt(result, CURLOPT_PROTOCOLS,
> > - get_curl_allowed_protocols());
> > + get_curl_allowed_protocols(-1));
>
> This covers internal redirects done by libcurl, but not the dumb-walker
> http-alternates nonsense. We have to feed the URL from http-alternates
> back to curl ourselves, so it uses CURLOPT_PROTOCOLS even though it
> should count as "not from the user".
>
> To fix that, I think we'd need something like:
>
> - get_curl_handle() stops setting these options, as it is done only
> once when the curl handle is initialized. Instead, the protocol
> restrictions should go into get_active_slot(), which is called for
> each request. The values set would remain the same, and be the
> baseline.
>
> - the http-walker.c code would need to know when it's requesting from
> the base URL, and when it's an alternate. I think this would depend
> on the position of the "alt" in in the linked list it keeps.
>
> - when requesting from an alternate, http-walker would set
> CURLOPT_PROTOCOLS with get_curl_allowed_protocols(0)
>
> I have to admit that it sounds like a fair bit of work for a pretty
> obscure case. You'd have to:
>
> 1. Turn http.allowRedirects to "true", to allow redirects even for
> non-initial contact.
>
> 2. Turn one of protocol.{http,https,ftp,ftps}.allow to "user" to
> restrict it from being used in a redirect.
>
> I'm tempted to punt on it and just do:
>
> if (http_follow_config == HTTP_FOLLOW_ALWAYS &&
> get_curl_allowed_protocols(0) != get_curl_allowed_protocols(-1))
> die("user-only protocol restrictions not implemented for http-alternates");
>
> which errs on the safe side. We could even shove that down into the case
> where we actually see some alternates, like:
>
> diff --git a/http-walker.c b/http-walker.c
> index c2f81cd6a..5bcc850b1 100644
> --- a/http-walker.c
> +++ b/http-walker.c
> @@ -160,6 +160,12 @@ static void prefetch(struct walker *walker, unsigned char *sha1)
> #endif
> }
>
> +static void check_alternates_protocol_restrictions(void)
> +{
> + if (get_curl_allowed_protocols(0) != get_curl_allowed_protocol(-1))
> + die("user-only protocol restrictions not implemented for http alternates");
> +}
> +
> static void process_alternates_response(void *callback_data)
> {
> struct alternates_request *alt_req =
> @@ -272,6 +278,7 @@ static void process_alternates_response(void *callback_data)
> /* skip "objects\n" at end */
> if (okay) {
> struct strbuf target = STRBUF_INIT;
> + check_alternates_protocol_restrictions();
> strbuf_add(&target, base, serverlen);
> strbuf_add(&target, data + i, posn - i - 7);
> warning("adding alternate object store: %s",
>
> I find it unlikely that anybody would ever care, but at least we'd do
> the safe thing. I dunno. Maybe I am just being lazy.
Well, that's unfortunate! It does sound like a more full-proof solution
to these dumb http alternates could be involved. I don't think your
simple "lazy" solution may be enough to not just die by default.
By default ftp/ftps will have a policy of "user only" which means they
will be set by the call to get_curl_allowed_protocol(-1) but not set by
get_curl_allowed_protocol(0). This would result in the call to
check_alternates_protocol_restrictions failing all the time unless the
user explicitly sets ftp/ftps to "always" or "never". If that is the
desired behavior then your proposed solution would be fine, otherwise we
may have to do the more involved approach.
--
Brandon Williams