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. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Jeff King committed
Sep 16, 2015 at 13:12 UTC
a5adaced2e13c135d5d9cc65be9eb95aa3bacedf
11 files changed
+254
-1
Documentation/git.txt
+32
@@ -1045,6 +1045,38 @@ GIT_ICASE_PATHSPECS::
1045
an operation has touched every ref (e.g., because you are
1046
cloning a repository to make a backup).
1047
1048
+`GIT_ALLOW_PROTOCOL`::
1049
+ If set, provide a colon-separated list of protocols which are
1050
+ allowed to be used with fetch/push/clone. This is useful to
1051
+ restrict recursive submodule initialization from an untrusted
1052
+ repository. Any protocol not mentioned will be disallowed (i.e.,
1053
+ this is a whitelist, not a blacklist). If the variable is not
1054
+ set at all, all protocols are enabled. The protocol names
1055
+ currently used by git are:
1056
+
1057
+ - `file`: any local file-based path (including `file://` URLs,
1058
+ or local paths)
1059
+
1060
+ - `git`: the anonymous git protocol over a direct TCP
1061
+ connection (or proxy, if configured)
1062
+
1063
+ - `ssh`: git over ssh (including `host:path` syntax,
1064
+ `git+ssh://`, etc).
1065
+
1066
+ - `rsync`: git over rsync
1067
+
1068
+ - `http`: git over http, both "smart http" and "dumb http".
1069
+ Note that this does _not_ include `https`; if you want both,
1070
+ you should specify both as `http:https`.
1071
+
1072
+ - any external helpers are named by their protocol (e.g., use
1073
+ `hg` to allow the `git-remote-hg` helper)
1074
++
1075
+Note that this controls only git's internal protocol selection.
1076
+If libcurl is used (e.g., by the `http` transport), it may
1077
+redirect to other protocols. There is not currently any way to
1078
+restrict this.
1079
+
1080
1081
Discussion[[Discussion]]
1082
------------------------
connect.c
+5
@@ -9,6 +9,7 @@
9
#include "url.h"
10
#include "string-list.h"
11
#include "sha1-array.h"
12
+#include "transport.h"
13
14
static char *server_capabilities;
15
static const char *parse_feature_value(const char *, const char *, int *);
@@ -694,6 +695,8 @@ struct child_process *git_connect(int fd[2], const char *url,
695
else
696
target_host = xstrdup(hostandport);
697
698
+ transport_check_allowed("git");
699
+
700
/* These underlying connection commands die() if they
701
* cannot connect.
702
*/
@@ -727,6 +730,7 @@ struct child_process *git_connect(int fd[2], const char *url,
730
int putty;
731
char *ssh_host = hostandport;
732
const char *port = NULL;
733
+ transport_check_allowed("ssh");
734
get_host_and_port(&ssh_host, &port);
735
736
if (!port)
@@ -768,6 +772,7 @@ struct child_process *git_connect(int fd[2], const char *url,
772
/* remove repo-local variables from the environment */
773
conn->env = local_repo_env;
774
conn->use_shell = 1;
775
+ transport_check_allowed("file");
776
}
777
argv_array_push(&conn->args, cmd.buf);
778
t/lib-proto-disable.sh
new
+96
@@ -0,0 +1,96 @@
1
+# Test routines for checking protocol disabling.
2
+
3
+# test cloning a particular protocol
4
+# $1 - description of the protocol
5
+# $2 - machine-readable name of the protocol
6
+# $3 - the URL to try cloning
7
+test_proto () {
8
+ desc=$1
9
+ proto=$2
10
+ url=$3
11
+
12
+ test_expect_success "clone $1 (enabled)" '
13
+ rm -rf tmp.git &&
14
+ (
15
+ GIT_ALLOW_PROTOCOL=$proto &&
16
+ export GIT_ALLOW_PROTOCOL &&
17
+ git clone --bare "$url" tmp.git
18
+ )
19
+ '
20
+
21
+ test_expect_success "fetch $1 (enabled)" '
22
+ (
23
+ cd tmp.git &&
24
+ GIT_ALLOW_PROTOCOL=$proto &&
25
+ export GIT_ALLOW_PROTOCOL &&
26
+ git fetch
27
+ )
28
+ '
29
+
30
+ test_expect_success "push $1 (enabled)" '
31
+ (
32
+ cd tmp.git &&
33
+ GIT_ALLOW_PROTOCOL=$proto &&
34
+ export GIT_ALLOW_PROTOCOL &&
35
+ git push origin HEAD:pushed
36
+ )
37
+ '
38
+
39
+ test_expect_success "push $1 (disabled)" '
40
+ (
41
+ cd tmp.git &&
42
+ GIT_ALLOW_PROTOCOL=none &&
43
+ export GIT_ALLOW_PROTOCOL &&
44
+ test_must_fail git push origin HEAD:pushed
45
+ )
46
+ '
47
+
48
+ test_expect_success "fetch $1 (disabled)" '
49
+ (
50
+ cd tmp.git &&
51
+ GIT_ALLOW_PROTOCOL=none &&
52
+ export GIT_ALLOW_PROTOCOL &&
53
+ test_must_fail git fetch
54
+ )
55
+ '
56
+
57
+ test_expect_success "clone $1 (disabled)" '
58
+ rm -rf tmp.git &&
59
+ (
60
+ GIT_ALLOW_PROTOCOL=none &&
61
+ export GIT_ALLOW_PROTOCOL &&
62
+ test_must_fail git clone --bare "$url" tmp.git
63
+ )
64
+ '
65
+}
66
+
67
+# set up an ssh wrapper that will access $host/$repo in the
68
+# trash directory, and enable it for subsequent tests.
69
+setup_ssh_wrapper () {
70
+ test_expect_success 'setup ssh wrapper' '
71
+ write_script ssh-wrapper <<-\EOF &&
72
+ echo >&2 "ssh: $*"
73
+ host=$1; shift
74
+ cd "$TRASH_DIRECTORY/$host" &&
75
+ eval "$*"
76
+ EOF
77
+ GIT_SSH="$PWD/ssh-wrapper" &&
78
+ export GIT_SSH &&
79
+ export TRASH_DIRECTORY
80
+ '
81
+}
82
+
83
+# set up a wrapper that can be used with remote-ext to
84
+# access repositories in the "remote" directory of trash-dir,
85
+# like "ext::fake-remote %S repo.git"
86
+setup_ext_wrapper () {
87
+ test_expect_success 'setup ext wrapper' '
88
+ write_script fake-remote <<-\EOF &&
89
+ echo >&2 "fake-remote: $*"
90
+ cd "$TRASH_DIRECTORY/remote" &&
91
+ eval "$*"
92
+ EOF
93
+ PATH=$TRASH_DIRECTORY:$PATH &&
94
+ export TRASH_DIRECTORY
95
+ '
96
+}
t/t5810-proto-disable-local.sh
new
+14
@@ -0,0 +1,14 @@
1
+#!/bin/sh
2
+
3
+test_description='test disabling of local paths in clone/fetch'
4
+. ./test-lib.sh
5
+. "$TEST_DIRECTORY/lib-proto-disable.sh"
6
+
7
+test_expect_success 'setup repository to clone' '
8
+ test_commit one
9
+'
10
+
11
+test_proto "file://" file "file://$PWD"
12
+test_proto "path" file .
13
+
14
+test_done
t/t5811-proto-disable-git.sh
new
+20
@@ -0,0 +1,20 @@
1
+#!/bin/sh
2
+
3
+test_description='test disabling of git-over-tcp in clone/fetch'
4
+. ./test-lib.sh
5
+. "$TEST_DIRECTORY/lib-proto-disable.sh"
6
+. "$TEST_DIRECTORY/lib-git-daemon.sh"
7
+start_git_daemon
8
+
9
+test_expect_success 'create git-accessible repo' '
10
+ bare="$GIT_DAEMON_DOCUMENT_ROOT_PATH/repo.git" &&
11
+ test_commit one &&
12
+ git --bare init "$bare" &&
13
+ git push "$bare" HEAD &&
14
+ >"$bare/git-daemon-export-ok" &&
15
+ git -C "$bare" config daemon.receivepack true
16
+'
17
+
18
+test_proto "git://" git "$GIT_DAEMON_URL/repo.git"
19
+
20
+test_done
t/t5812-proto-disable-http.sh
new
+20
@@ -0,0 +1,20 @@
1
+#!/bin/sh
2
+
3
+test_description='test disabling of git-over-http in clone/fetch'
4
+. ./test-lib.sh
5
+. "$TEST_DIRECTORY/lib-proto-disable.sh"
6
+. "$TEST_DIRECTORY/lib-httpd.sh"
7
+start_httpd
8
+
9
+test_expect_success 'create git-accessible repo' '
10
+ bare="$HTTPD_DOCUMENT_ROOT_PATH/repo.git" &&
11
+ test_commit one &&
12
+ git --bare init "$bare" &&
13
+ git push "$bare" HEAD &&
14
+ git -C "$bare" config http.receivepack true
15
+'
16
+
17
+test_proto "smart http" http "$HTTPD_URL/smart/repo.git"
18
+
19
+stop_httpd
20
+test_done
t/t5813-proto-disable-ssh.sh
new
+20
@@ -0,0 +1,20 @@
1
+#!/bin/sh
2
+
3
+test_description='test disabling of git-over-ssh in clone/fetch'
4
+. ./test-lib.sh
5
+. "$TEST_DIRECTORY/lib-proto-disable.sh"
6
+
7
+setup_ssh_wrapper
8
+
9
+test_expect_success 'setup repository to clone' '
10
+ test_commit one &&
11
+ mkdir remote &&
12
+ git init --bare remote/repo.git &&
13
+ git push remote/repo.git HEAD
14
+'
15
+
16
+test_proto "host:path" ssh "remote:repo.git"
17
+test_proto "ssh://" ssh "ssh://remote/$PWD/remote/repo.git"
18
+test_proto "git+ssh://" ssh "git+ssh://remote/$PWD/remote/repo.git"
19
+
20
+test_done
t/t5814-proto-disable-ext.sh
new
+18
@@ -0,0 +1,18 @@
1
+#!/bin/sh
2
+
3
+test_description='test disabling of remote-helper paths in clone/fetch'
4
+. ./test-lib.sh
5
+. "$TEST_DIRECTORY/lib-proto-disable.sh"
6
+
7
+setup_ext_wrapper
8
+
9
+test_expect_success 'setup repository to clone' '
10
+ test_commit one &&
11
+ mkdir remote &&
12
+ git init --bare remote/repo.git &&
13
+ git push remote/repo.git HEAD
14
+'
15
+
16
+test_proto "remote-helper" ext "ext::fake-remote %S repo.git"
17
+
18
+test_done
transport-helper.c
+2
@@ -1038,6 +1038,8 @@ int transport_helper_init(struct transport *transport, const char *name)
1038
struct helper_data *data = xcalloc(1, sizeof(*data));
1039
data->name = name;
1040
1041
+ transport_check_allowed(name);
1042
+
1043
if (getenv("GIT_TRANSPORT_HELPER_DEBUG"))
1044
debug = 1;
1045
transport.c
+20
-1
@@ -909,6 +909,20 @@ static int external_specification_len(const char *url)
909
return strchr(url, ':') - url;
910
}
911
912
+void transport_check_allowed(const char *type)
913
+{
914
+ struct string_list allowed = STRING_LIST_INIT_DUP;
915
+ const char *v = getenv("GIT_ALLOW_PROTOCOL");
916
+
917
+ if (!v)
918
+ return;
919
+
920
+ string_list_split(&allowed, v, ':', -1);
921
+ if (!unsorted_string_list_has_string(&allowed, type))
922
+ die("transport '%s' not allowed", type);
923
+ string_list_clear(&allowed, 0);
924
+}
925
+
926
struct transport *transport_get(struct remote *remote, const char *url)
927
{
928
const char *helper;
@@ -940,12 +954,14 @@ struct transport *transport_get(struct remote *remote, const char *url)
954
if (helper) {
955
transport_helper_init(ret, helper);
956
} else if (starts_with(url, "rsync:")) {
957
+ transport_check_allowed("rsync");
958
ret->get_refs_list = get_refs_via_rsync;
959
ret->fetch = fetch_objs_via_rsync;
960
ret->push = rsync_transport_push;
961
ret->smart_options = NULL;
962
} else if (url_is_local_not_ssh(url) && is_file(url) && is_bundle(url, 1)) {
963
struct bundle_transport_data *data = xcalloc(1, sizeof(*data));
964
+ transport_check_allowed("file");
965
ret->data = data;
966
ret->get_refs_list = get_refs_from_bundle;
967
ret->fetch = fetch_refs_from_bundle;
@@ -957,7 +973,10 @@ struct transport *transport_get(struct remote *remote, const char *url)
973
|| starts_with(url, "ssh://")
974
|| starts_with(url, "git+ssh://")
975
|| starts_with(url, "ssh+git://")) {
960
- /* These are builtin smart transports. */
976
+ /*
977
+ * These are builtin smart transports; "allowed" transports
978
+ * will be checked individually in git_connect.
979
+ */
980
struct git_transport_data *data = xcalloc(1, sizeof(*data));
981
ret->data = data;
982
ret->set_option = NULL;
transport.h
+7
@@ -132,6 +132,13 @@ struct transport {
132
/* Returns a transport suitable for the url */
133
struct transport *transport_get(struct remote *, const char *);
134
135
+/*
136
+ * Check whether a transport is allowed by the environment,
137
+ * and die otherwise. type should generally be the URL scheme,
138
+ * as described in Documentation/git.txt
139
+ */
140
+void transport_check_allowed(const char *type);
141
+
142
/* Transport options which apply to git:// and scp-style URLs */
143
144
/* The program to use on the remote side to send a pack */