From 76381ee08cb412775863d2a165916448e8950009 Mon Sep 17 00:00:00 2001
From: Petr Stodulka <pstodulk@redhat.com>
Date: Fri, 23 Oct 2015 17:21:13 +0200
Subject: [PATCH 2/5] transport: add a protocol-whitelist environment variable
If we are cloning an untrusted remote repository into a
sandbox, we may also want to fetch remote submodules in
order to get the complete view as intended by the other
side. However, that opens us up to attacks where a malicious
user gets us to clone something they would not otherwise
have access to (this is not necessarily a problem by itself,
but we may then act on the cloned contents in a way that
exposes them to the attacker).
Ideally such a setup would sandbox git entirely away from
high-value items, but this is not always practical or easy
to set up (e.g., OS network controls may block multiple
protocols, and we would want to enable some but not others).
We can help this case by providing a way to restrict
particular protocols. We use a whitelist in the environment.
This is more annoying to set up than a blacklist, but
defaults to safety if the set of protocols git supports
grows). If no whitelist is specified, we continue to default
to allowing all protocols (this is an "unsafe" default, but
since the minority of users will want this sandboxing
effect, it is the only sensible one).
A note on the tests: ideally these would all be in a single
test file, but the git-daemon and httpd test infrastructure
is an all-or-nothing proposition rather than a test-by-test
prerequisite. By putting them all together, we would be
unable to test the file-local code on machines without
apache.
---
Documentation/git.txt | 32 ++++++++++++++++++++++++++++++++
connect.c | 4 ++++
transport-helper.c | 2 ++
transport.c | 22 +++++++++++++++++++++-
transport.h | 7 +++++++
5 files changed, 66 insertions(+), 1 deletion(-)
diff --git a/Documentation/git.txt b/Documentation/git.txt
index 3d54378..4643814 100644
--- a/Documentation/git.txt
+++ b/Documentation/git.txt
@@ -951,6 +951,38 @@ GIT_ICASE_PATHSPECS::
variable when it is invoked as the top level command by the
end user, to be recorded in the body of the reflog.
+`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:
+
+ - `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,
+ `git+ssh://`, etc).
+
+ - `rsync`: git over rsync
+
+ - `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)
++
+Note that this controls only git's internal protocol selection.
+If libcurl is used (e.g., by the `http` transport), it may
+redirect to other protocols. There is not currently any way to
+restrict this.
+
Discussion[[Discussion]]
------------------------
diff --git a/connect.c b/connect.c
index 4150412..bafd5cb 100644
--- a/connect.c
+++ b/connect.c
@@ -9,6 +9,7 @@
#include "url.h"
#include "string-list.h"
#include "sha1-array.h"
+#include "transport.h"
static char *server_capabilities;
static const char *parse_feature_value(const char *, const char *, int *);
@@ -683,6 +684,7 @@ struct child_process *git_connect(int fd[2], const char *url,
* cannot connect.
*/
char *target_host = xstrdup(hostandport);
+ transport_check_allowed("git");
if (git_use_proxy(hostandport))
conn = git_proxy_connect(fd, hostandport);
else
@@ -713,6 +715,7 @@ struct child_process *git_connect(int fd[2], const char *url,
int putty = ssh && strcasestr(ssh, "plink");
char *ssh_host = hostandport;
const char *port = NULL;
+ transport_check_allowed("ssh");
get_host_and_port(&ssh_host, &port);
port = get_port_numeric(port);
@@ -731,6 +734,7 @@ struct child_process *git_connect(int fd[2], const char *url,
/* remove repo-local variables from the environment */
conn->env = local_repo_env;
conn->use_shell = 1;
+ transport_check_allowed("file");
}
*arg++ = cmd.buf;
*arg = NULL;
diff --git a/transport-helper.c b/transport-helper.c
index ad72fbd..87a14a5 100644
--- a/transport-helper.c
+++ b/transport-helper.c
@@ -1005,6 +1005,8 @@ int transport_helper_init(struct transport *transport, const char *name)
struct helper_data *data = xcalloc(sizeof(*data), 1);
data->name = name;
+ transport_check_allowed(name);
+
if (getenv("GIT_TRANSPORT_HELPER_DEBUG"))
debug = 1;
diff --git a/transport.c b/transport.c
index ca7bb44..93d7ced 100644
--- a/transport.c
+++ b/transport.c
@@ -913,6 +913,20 @@ static int external_specification_len(const char *url)
return strchr(url, ':') - url;
}
+void transport_check_allowed(const char *type)
+{
+ struct string_list allowed = STRING_LIST_INIT_DUP;
+ const char *v = getenv("GIT_ALLOW_PROTOCOL");
+
+ if (!v)
+ return;
+
+ string_list_split(&allowed, v, ':', -1);
+ if (!unsorted_string_list_has_string(&allowed, type))
+ die("transport '%s' not allowed", type);
+ string_list_clear(&allowed, 0);
+}
+
struct transport *transport_get(struct remote *remote, const char *url)
{
const char *helper;
@@ -944,12 +958,14 @@ struct transport *transport_get(struct remote *remote, const char *url)
if (helper) {
transport_helper_init(ret, helper);
} else if (starts_with(url, "rsync:")) {
+ transport_check_allowed("rsync");
ret->get_refs_list = get_refs_via_rsync;
ret->fetch = fetch_objs_via_rsync;
ret->push = rsync_transport_push;
ret->smart_options = NULL;
} else if (url_is_local_not_ssh(url) && is_file(url) && is_bundle(url, 1)) {
struct bundle_transport_data *data = xcalloc(1, sizeof(*data));
+ transport_check_allowed("file");
ret->data = data;
ret->get_refs_list = get_refs_from_bundle;
ret->fetch = fetch_refs_from_bundle;
@@ -961,7 +977,10 @@ struct transport *transport_get(struct remote *remote, const char *url)
|| starts_with(url, "ssh://")
|| starts_with(url, "git+ssh://")
|| starts_with(url, "ssh+git://")) {
- /* These are builtin smart transports. */
+ /*
+ * These are builtin smart transports; "allowed" transports
+ * will be checked individually in git_connect.
+ */
struct git_transport_data *data = xcalloc(1, sizeof(*data));
ret->data = data;
ret->set_option = NULL;
diff --git a/transport.h b/transport.h
index 02ea248..c1447f1 100644
--- a/transport.h
+++ b/transport.h
@@ -130,6 +130,13 @@ struct transport {
/* Returns a transport suitable for the url */
struct transport *transport_get(struct remote *, const char *);
+/*
+ * Check whether a transport is allowed by the environment,
+ * and die otherwise. type should generally be the URL scheme,
+ * as described in Documentation/git.txt
+ */
+void transport_check_allowed(const char *type);
+
/* Transport options which apply to git:// and scp-style URLs */
/* The program to use on the remote side to send a pack */
--
2.1.0