Re: [PATCH v4 2/2] transport: add protocol policy config option

On Mon, Nov 07, 2016 at 11:35:23AM -0800, Brandon Williams wrote:

Previously the `GIT_ALLOW_PROTOCOL` environment variable was used to
specify a whitelist of protocols to be used in clone/fetch/push
commands.  This patch introduces new configuration options for more
fine-grained control for allowing/disallowing protocols.  This also has
the added benefit of allowing easier construction of a protocol
whitelist on systems where setting an environment variable is
non-trivial.

Now users can specify a policy to be used for each type of protocol via
the 'protocol.<name>.allow' config option.  A default policy for all
unconfigured protocols can be set with the 'protocol.allow' config
option.  If no user configured default is made git, by default, will
allow known-safe protocols (http, https, git, ssh, file), disallow

A minor nit, but in "If no user configured default is made git, by
default, will..." the second "by default" is redundant. And possibly
misleading. This _is_ the default case, there is no other way to change
it. :)

+protocol.<name>.allow::
+	Set a policy to be used by protocol <name> with clone/fetch/push commands.

`<name>` isn't defined here at all.  I still think the list of protocols
should go here, but at the very least, you need to point the user to the
existing list in git(1).

 `GIT_ALLOW_PROTOCOL`::
-	If set, provide a colon-separated list of protocols which are
-	allowed to be used with fetch/push/clone. This is useful to
-	restrict recursive submodule initialization from an untrusted
-	repository. Any protocol not mentioned will be disallowed (i.e.,
-	this is a whitelist, not a blacklist). If the variable is not
-	set at all, all protocols are enabled.  The protocol names
-	currently used by git are:
+	The preferred way to configure allowed protocols is done through the
+	config interface, though this setting takes precedences.  See

s/precedences/precedence/.

I actually wonder if we should even drop "the preferred way" here. I had
initially thought we would want it just for backwards-compatibility, but
I actually think it is useful in its own right as a shorthand for more
complicated config (and since we have to keep it around effectively
forever anyway, there's no real cost to continuing to call it a feature
versus a deprecated feature).

I'm including a squashable patch at the end of this email with suggested
wording (and which also moves the protocol list).

+	test_expect_success "clone $desc (env var has precedence)" '
+		rm -rf tmp.git &&
+		(
+			GIT_ALLOW_PROTOCOL=none &&
+			export GIT_ALLOW_PROTOCOL &&
+			test_must_fail git -c protocol.$proto.allow=always clone --bare "$url" tmp.git
+		)
+	'

This test is a good addition in this round.

I suppose we could test also that GIT_ALLOW_PROTOCOL overrides
protocol.allow, but I'm not sure if there is a point. If git were a
black box, it's a thing I might check, but we know from the design that
this is an unlikely bug (and that the implementation is unlikely to
change in a way to cause it). So I could go either way.

[...]

The rest of it looks good to me.

Squashable documentation suggestions are below.

-Peff

---

diff --git a/Documentation/config.txt b/Documentation/config.txt
index e89b33f9e..a9dc23f82 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt

@@ -2331,7 +2331,28 @@ protocol.allow::
 --
 
 protocol.<name>.allow::
-	Set a policy to be used by protocol <name> with clone/fetch/push commands.
+	Set a policy to be used by protocol `<name>` with clone/fetch/push
+	commands. See `protocol.allow` above for the available policies.
++
+The protocol names currently used by git are:
++
+--
+  - `file`: any local file-based path (including `file://` URLs,
+	    or local paths)
+
+  - `git`: the anonymous git protocol over a direct TCP
+    connection (or proxy, if configured)
+
+  - `ssh`: git over ssh (including `host:path` syntax,
+    `ssh://`, etc).
+
+  - `http`: git over http, both "smart http" and "dumb http".
+    Note that this does _not_ include `https`; if you want to configure
+    both, you must do so individually.
+
+  - any external helpers are named by their protocol (e.g., use
+    `hg` to allow the `git-remote-hg` helper)
+--
 
 pull.ff::
 	By default, Git does not create an extra merge commit when merging

diff --git a/Documentation/git.txt b/Documentation/git.txt
index c9823e34a..c52cec840 100644
--- a/Documentation/git.txt
+++ b/Documentation/git.txt

@@ -1150,30 +1150,13 @@ of clones and fetches.
 	cloning a repository to make a backup).
 
 `GIT_ALLOW_PROTOCOL`::
-	The preferred way to configure allowed protocols is done through the
-	config interface, though this setting takes precedences.  See
-	linkgit:git-config[1] for more details.  If set to a colon-separated
-	list of protocols, behave as if `protocol.allow` is set to `never`, and
-	each of the listed protocols has `protocol.<name>.allow` set to
-	`always`.  In other words, any protocol not mentioned will be
-	disallowed (i.e., this is a whitelist, not a blacklist).  The protocol
-	names currently used by git are:
-
-	  - `file`: any local file-based path (including `file://` URLs,
-	    or local paths)
-
-	  - `git`: the anonymous git protocol over a direct TCP
-	    connection (or proxy, if configured)
-
-	  - `ssh`: git over ssh (including `host:path` syntax,
-	    `ssh://`, etc).
-
-	  - `http`: git over http, both "smart http" and "dumb http".
-	    Note that this does _not_ include `https`; if you want both,
-	    you should specify both as `http:https`.
-
-	  - any external helpers are named by their protocol (e.g., use
-	    `hg` to allow the `git-remote-hg` helper)
+	If set to a colon-separated list of protocols, behave as if
+	`protocol.allow` is set to `never`, and each of the listed
+	protocols has `protocol.<name>.allow` set to `always`
+	(overriding any existing configuration). In other words, any
+	protocol not mentioned will be disallowed (i.e., this is a
+	whitelist, not a blacklist). See the description of
+	`protocol.allow` in linkgit:git-config[1] for more details.
 
 `GIT_PROTOCOL_FROM_USER`::
 	Set to 0 to prevent protocols used by fetch/push/clone which are