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fix arbitrary code execution via crafted URLs

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Resolves: #1269797
This commit is contained in:
Petr Stodulka 2015-10-28 17:46:44 +01:00
commit 9f21141ed7
6 changed files with 579 additions and 4 deletions
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207
0001-transport-add-a-protocol-whitelist-environment-varia.patch Normal file
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@ -0,0 +1,207 @@
From 0730270cd672467c12a3f3bf36336d169700269a Mon Sep 17 00:00:00 2001
From: Petr Stodulka <pstodulk@redhat.com>
Date: Wed, 28 Oct 2015 17:22:13 +0100
Subject: [PATCH 1/5] 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 | 31 +++++++++++++++++++++++++++++++
connect.c | 5 +++++
transport-helper.c | 2 ++
transport.c | 21 ++++++++++++++++++++-
transport.h | 7 +++++++
5 files changed, 65 insertions(+), 1 deletion(-)
diff --git a/Documentation/git.txt b/Documentation/git.txt
index f4cb5cb..71ba92b 100644
--- a/Documentation/git.txt
+++ b/Documentation/git.txt
@@ -1069,6 +1069,37 @@ GIT_ICASE_PATHSPECS::
an operation has touched every ref (e.g., because you are
cloning a repository to make a backup).
+`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 c0144d8..27a706f 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 *);
@@ -694,6 +695,8 @@ struct child_process *git_connect(int fd[2], const char *url,
else
target_host = xstrdup(hostandport);
+ transport_check_allowed("git");
+
/* These underlying connection commands die() if they
* cannot connect.
*/
@@ -727,6 +730,7 @@ struct child_process *git_connect(int fd[2], const char *url,
int putty, tortoiseplink = 0;
char *ssh_host = hostandport;
const char *port = NULL;
+ transport_check_allowed("ssh");
get_host_and_port(&ssh_host, &port);
if (!port)
@@ -781,6 +785,7 @@ 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");
}
argv_array_push(&conn->args, cmd.buf);
diff --git a/transport-helper.c b/transport-helper.c
index 5d99a6b..b486441 100644
--- a/transport-helper.c
+++ b/transport-helper.c
@@ -1039,6 +1039,8 @@ int transport_helper_init(struct transport *transport, const char *name)
struct helper_data *data = xcalloc(1, sizeof(*data));
data->name = name;
+ transport_check_allowed(name);
+
if (getenv("GIT_TRANSPORT_HELPER_DEBUG"))
debug = 1;
diff --git a/transport.c b/transport.c
index 40692f8..ad1ae7f 100644
--- a/transport.c
+++ b/transport.c
@@ -912,6 +912,20 @@ 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;
@@ -943,12 +957,14 @@ 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;
@@ -960,7 +976,10 @@ 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 18d2cf8..742027f 100644
--- a/transport.h
+++ b/transport.h
@@ -133,6 +133,13 @@ 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

108
0002-submodule-allow-only-certain-protocols-for-submodule.patch Normal file
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@ -0,0 +1,108 @@
From 772390a8977b0c667aefe0ba4989d4f36f3d1832 Mon Sep 17 00:00:00 2001
From: Jeff King <peff@peff.net>
Date: Wed, 16 Sep 2015 13:13:12 -0400
Subject: [PATCH 2/5] submodule: allow only certain protocols for submodule
fetches
Some protocols (like git-remote-ext) can execute arbitrary
code found in the URL. The URLs that submodules use may come
from arbitrary sources (e.g., .gitmodules files in a remote
repository). Let's restrict submodules to fetching from a
known-good subset of protocols.
Note that we apply this restriction to all submodule
commands, whether the URL comes from .gitmodules or not.
This is more restrictive than we need to be; for example, in
the tests we run:
git submodule add ext::...
which should be trusted, as the URL comes directly from the
command line provided by the user. But doing it this way is
simpler, and makes it much less likely that we would miss a
case. And since such protocols should be an exception
(especially because nobody who clones from them will be able
to update the submodules!), it's not likely to inconvenience
anyone in practice.
Reported-by: Blake Burkhart <bburky@bburky.com>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
git-submodule.sh | 9 +++++++++
t/t5815-submodule-protos.sh | 43 +++++++++++++++++++++++++++++++++++++++++++
2 files changed, 52 insertions(+)
create mode 100755 t/t5815-submodule-protos.sh
diff --git a/git-submodule.sh b/git-submodule.sh
index 36797c3..78c2740 100755
--- a/git-submodule.sh
+++ b/git-submodule.sh
@@ -22,6 +22,15 @@ require_work_tree
wt_prefix=$(git rev-parse --show-prefix)
cd_to_toplevel
+# Restrict ourselves to a vanilla subset of protocols; the URLs
+# we get are under control of a remote repository, and we do not
+# want them kicking off arbitrary git-remote-* programs.
+#
+# If the user has already specified a set of allowed protocols,
+# we assume they know what they're doing and use that instead.
+: ${GIT_ALLOW_PROTOCOL=file:git:http:https:ssh}
+export GIT_ALLOW_PROTOCOL
+
command=
branch=
force=
diff --git a/t/t5815-submodule-protos.sh b/t/t5815-submodule-protos.sh
new file mode 100755
index 0000000..06f55a1
--- /dev/null
+++ b/t/t5815-submodule-protos.sh
@@ -0,0 +1,43 @@
+#!/bin/sh
+
+test_description='test protocol whitelisting with submodules'
+. ./test-lib.sh
+. "$TEST_DIRECTORY"/lib-proto-disable.sh
+
+setup_ext_wrapper
+setup_ssh_wrapper
+
+test_expect_success 'setup repository with submodules' '
+ mkdir remote &&
+ git init remote/repo.git &&
+ (cd remote/repo.git && test_commit one) &&
+ # submodule-add should probably trust what we feed it on the cmdline,
+ # but its implementation is overly conservative.
+ GIT_ALLOW_PROTOCOL=ssh git submodule add remote:repo.git ssh-module &&
+ GIT_ALLOW_PROTOCOL=ext git submodule add "ext::fake-remote %S repo.git" ext-module &&
+ git commit -m "add submodules"
+'
+
+test_expect_success 'clone with recurse-submodules fails' '
+ test_must_fail git clone --recurse-submodules . dst
+'
+
+test_expect_success 'setup individual updates' '
+ rm -rf dst &&
+ git clone . dst &&
+ git -C dst submodule init
+'
+
+test_expect_success 'update of ssh allowed' '
+ git -C dst submodule update ssh-module
+'
+
+test_expect_success 'update of ext not allowed' '
+ test_must_fail git -C dst submodule update ext-module
+'
+
+test_expect_success 'user can override whitelist' '
+ GIT_ALLOW_PROTOCOL=ext git -C dst submodule update ext-module
+'
+
+test_done
--
2.1.0

107
0003-transport-refactor-protocol-whitelist-code.patch Normal file
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@ -0,0 +1,107 @@
From 92773f7741ead61f9bdbdaf28272cca405da4fd7 Mon Sep 17 00:00:00 2001
From: Jeff King <peff@peff.net>
Date: Tue, 22 Sep 2015 18:03:49 -0400
Subject: [PATCH 3/5] transport: refactor protocol whitelist code
The current callers only want to die when their transport is
prohibited. But future callers want to query the mechanism
without dying.
Let's break out a few query functions, and also save the
results in a static list so we don't have to re-parse for
each query.
Based-on-a-patch-by: Blake Burkhart <bburky@bburky.com>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
transport.c | 38 ++++++++++++++++++++++++++++++--------
transport.h | 15 +++++++++++++--
2 files changed, 43 insertions(+), 10 deletions(-)
diff --git a/transport.c b/transport.c
index ad1ae7f..164a716 100644
--- a/transport.c
+++ b/transport.c
@@ -912,18 +912,40 @@ static int external_specification_len(const char *url)
return strchr(url, ':') - url;
}
-void transport_check_allowed(const char *type)
+static const struct string_list *protocol_whitelist(void)
{
- struct string_list allowed = STRING_LIST_INIT_DUP;
- const char *v = getenv("GIT_ALLOW_PROTOCOL");
+ static int enabled = -1;
+ static struct string_list allowed = STRING_LIST_INIT_DUP;
+
+ if (enabled < 0) {
+ const char *v = getenv("GIT_ALLOW_PROTOCOL");
+ if (v) {
+ string_list_split(&allowed, v, ':', -1);
+ string_list_sort(&allowed);
+ enabled = 1;
+ } else {
+ enabled = 0;
+ }
+ }
- if (!v)
- return;
+ return enabled ? &allowed : NULL;
+}
+
+int is_transport_allowed(const char *type)
+{
+ const struct string_list *allowed = protocol_whitelist();
+ return !allowed || string_list_has_string(allowed, type);
+}
- string_list_split(&allowed, v, ':', -1);
- if (!unsorted_string_list_has_string(&allowed, type))
+void transport_check_allowed(const char *type)
+{
+ if (!is_transport_allowed(type))
die("transport '%s' not allowed", type);
- string_list_clear(&allowed, 0);
+}
+
+int transport_restrict_protocols(void)
+{
+ return !!protocol_whitelist();
}
struct transport *transport_get(struct remote *remote, const char *url)
diff --git a/transport.h b/transport.h
index 742027f..9770777 100644
--- a/transport.h
+++ b/transport.h
@@ -134,12 +134,23 @@ struct transport {
struct transport *transport_get(struct remote *, const char *);
/*
+ * Check whether a transport is allowed by the environment. Type should
+ * generally be the URL scheme, as described in Documentation/git.txt
+ */
+int is_transport_allowed(const char *type);
+
+/*
* 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
+ * and die otherwise.
*/
void transport_check_allowed(const char *type);
+/*
+ * Returns true if the user has attempted to turn on protocol
+ * restrictions at all.
+ */
+int transport_restrict_protocols(void);
+
/* 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

106
0004-http-limit-redirection-to-protocol-whitelist.patch Normal file
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@ -0,0 +1,106 @@
From b82f2606edf3640e40ca4d4e0091fd15104c765c Mon Sep 17 00:00:00 2001
From: Petr Stodulka <pstodulk@redhat.com>
Date: Wed, 28 Oct 2015 17:27:58 +0100
Subject: [PATCH 4/5] http: limit redirection to protocol-whitelist
Previously, libcurl would follow redirection to any protocol
it was compiled for support with. This is desirable to allow
redirection from HTTP to HTTPS. However, it would even
successfully allow redirection from HTTP to SFTP, a protocol
that git does not otherwise support at all. Furthermore
git's new protocol-whitelisting could be bypassed by
following a redirect within the remote helper, as it was
only enforced at transport selection time.
This patch limits redirects within libcurl to HTTP, HTTPS,
FTP and FTPS. If there is a protocol-whitelist present, this
list is limited to those also allowed by the whitelist. As
redirection happens from within libcurl, it is impossible
for an HTTP redirect to a protocol implemented within
another remote helper.
When the curl version git was compiled with is too old to
support restrictions on protocol redirection, we warn the
user if GIT_ALLOW_PROTOCOL restrictions were requested. This
is a little inaccurate, as even without that variable in the
environment, we would still restrict SFTP, etc, and we do
not warn in that case. But anything else means we would
literally warn every time git accesses an http remote.
This commit includes a test, but it is not as robust as we
would hope. It redirects an http request to ftp, and checks
that curl complained about the protocol, which means that we
are relying on curl's specific error message to know what
happened. Ideally we would redirect to a working ftp server
and confirm that we can clone without protocol restrictions,
and not with them. But we do not have a portable way of
providing an ftp server, nor any other protocol that curl
supports (https is the closest, but we would have to deal
with certificates).
---
Documentation/git.txt | 6 +-----
http.c | 17 +++++++++++++++++
2 files changed, 18 insertions(+), 5 deletions(-)
diff --git a/Documentation/git.txt b/Documentation/git.txt
index 71ba92b..d65e6bf 100644
--- a/Documentation/git.txt
+++ b/Documentation/git.txt
@@ -1095,11 +1095,7 @@ GIT_ICASE_PATHSPECS::
- 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/http.c b/http.c
index e9c6fdd..8a71f9e 100644
--- a/http.c
+++ b/http.c
@@ -9,6 +9,7 @@
#include "version.h"
#include "pkt-line.h"
#include "gettext.h"
+#include "transport.h"
int active_requests;
int http_is_verbose;
@@ -340,6 +341,7 @@ static void set_curl_keepalive(CURL *c)
static CURL *get_curl_handle(void)
{
CURL *result = curl_easy_init();
+ long allowed_protocols = 0;
if (!result)
die("curl_easy_init failed");
@@ -399,6 +401,21 @@ static CURL *get_curl_handle(void)
#elif LIBCURL_VERSION_NUM >= 0x071101
curl_easy_setopt(result, CURLOPT_POST301, 1);
#endif
+#if LIBCURL_VERSION_NUM >= 0x071304
+ if (is_transport_allowed("http"))
+ allowed_protocols |= CURLPROTO_HTTP;
+ if (is_transport_allowed("https"))
+ allowed_protocols |= CURLPROTO_HTTPS;
+ if (is_transport_allowed("ftp"))
+ allowed_protocols |= CURLPROTO_FTP;
+ if (is_transport_allowed("ftps"))
+ allowed_protocols |= CURLPROTO_FTPS;
+ curl_easy_setopt(result, CURLOPT_REDIR_PROTOCOLS, allowed_protocols);
+#else
+ if (transport_restrict_protocols())
+ warning("protocol restrictions not applied to curl redirects because\n"
+ "your curl version is too old (>= 7.19.4)");
+#endif
if (getenv("GIT_CURL_VERBOSE"))
curl_easy_setopt(result, CURLOPT_VERBOSE, 1);
--
2.1.0

31
0005-http-limit-redirection-depth.patch Normal file
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@ -0,0 +1,31 @@
From 653f7dc379a20d79728e6e77a07a718d9475e4c0 Mon Sep 17 00:00:00 2001
From: Petr Stodulka <pstodulk@redhat.com>
Date: Wed, 28 Oct 2015 17:30:24 +0100
Subject: [PATCH 5/5] http: limit redirection depth
By default, libcurl will follow circular http redirects
forever. Let's put a cap on this so that somebody who can
trigger an automated fetch of an arbitrary repository (e.g.,
for CI) cannot convince git to loop infinitely.
The value chosen is 20, which is the same default that
Firefox uses.
---
http.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/http.c b/http.c
index 8a71f9e..45348fb 100644
--- a/http.c
+++ b/http.c
@@ -396,6 +396,7 @@ static CURL *get_curl_handle(void)
}
curl_easy_setopt(result, CURLOPT_FOLLOWLOCATION, 1);
+ curl_easy_setopt(result, CURLOPT_MAXREDIRS, 20);
#if LIBCURL_VERSION_NUM >= 0x071301
curl_easy_setopt(result, CURLOPT_POSTREDIR, CURL_REDIR_POST_ALL);
#elif LIBCURL_VERSION_NUM >= 0x071101
--
2.1.0

24
git.spec
View file

@ -44,7 +44,7 @@
Name: git
Version: 2.4.3
Release: 6%{?dist}
Release: 7%{?dist}
Summary: Fast Version Control System
License: GPLv2
Group: Development/Tools
@ -67,6 +67,13 @@ Patch3: git-1.7-el5-emacs-support.patch
Patch4: git-infinite-loop.patch
Patch5: git-2.4.3-stash-revert.patch
# set of patches for security bug (solved since 2.6.1)
Patch6: 0001-transport-add-a-protocol-whitelist-environment-varia.patch
Patch7: 0002-submodule-allow-only-certain-protocols-for-submodule.patch
Patch8: 0003-transport-refactor-protocol-whitelist-code.patch
Patch9: 0004-http-limit-redirection-to-protocol-whitelist.patch
Patch10: 0005-http-limit-redirection-depth.patch
BuildRoot: %{_tmppath}/%{name}-%{version}-%{release}-root-%(%{__id_u} -n)
%if ! %{use_prebuilt_docs} && ! 0%{?_without_docs}
@ -295,6 +302,11 @@ Requires: emacs-git = %{version}-%{release}
%endif
%patch4 -p1
%patch5 -p1
%patch6 -p1
%patch7 -p1
%patch8 -p1
%patch9 -p1
%patch10 -p1
%if %{use_prebuilt_docs}
mkdir -p prebuilt_docs/{html,man}
@ -613,14 +625,18 @@ rm -rf %{buildroot}
# No files for you!
%changelog
* Mon Jun 22 2015 Petr Stodulka <pstodulk@gmail.com> - 2.4.3-6
* Wed Oct 28 2015 Petr Stodulka <pstodulk@redhat.com> - 2.4.3-7
- fix arbitrary code execution via crafted URLs
Resolves: #1269797
* Mon Jun 22 2015 Petr Stodulka <pstodulk@redhat.com> - 2.4.3-6
- fix #1242034 - "git stash save -k" followed by "git stash apply" fails
used upstream solution from git-2.4.6 (revert relevant commit)
* Mon Jun 22 2015 Petr Stodulka <pstodulk@gmail.com> - 2.4.3-5
* Mon Jun 22 2015 Petr Stodulka <pstodulk@redhat.com> - 2.4.3-5
- apply git-infinite-loop.patch
* Mon Jun 22 2015 Petr Stodulka <pstodulk@gmail.com> - 2.4.3-4
* Mon Jun 22 2015 Petr Stodulka <pstodulk@redhat.com> - 2.4.3-4
- git-svn - added requires for perl-Digest-MD5 (#1218176)
- solve troubles with infinite loop due to broken symlink (probably
shouldn't be problem here, but it's reproducible manually)