From 038655c9ee29ee659e5fede4d36871cf8ccef803 Mon Sep 17 00:00:00 2001
From: Simon McVittie <smcv@collabora.com>
Date: Mon, 7 Dec 2020 18:08:16 +0000
Subject: [PATCH 01/10] common: Add a backport of
G_DBUS_METHOD_INVOCATION_HANDLED
This is syntactic sugar added in GLib 2.67.0, which makes it more clearly
correct when we return TRUE after a GDBus error.
Signed-off-by: Simon McVittie <smcv@collabora.com>
---
common/flatpak-utils-base-private.h | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/common/flatpak-utils-base-private.h b/common/flatpak-utils-base-private.h
index 181a0c95..9d10a530 100644
--- a/common/flatpak-utils-base-private.h
+++ b/common/flatpak-utils-base-private.h
@@ -22,6 +22,12 @@
#define __FLATPAK_UTILS_BASE_H__
#include <glib.h>
+#include <gio/gio.h>
+
+#ifndef G_DBUS_METHOD_INVOCATION_HANDLED
+# define G_DBUS_METHOD_INVOCATION_HANDLED TRUE
+# define G_DBUS_METHOD_INVOCATION_UNHANDLED FALSE
+#endif
char *flatpak_get_timezone (void);
--
2.29.2
From 6ed3e235459f5fe8b58aecbab744166a5ee66f9d Mon Sep 17 00:00:00 2001
From: Simon McVittie <smcv@collabora.com>
Date: Sun, 10 Jan 2021 16:11:28 +0000
Subject: [PATCH 02/10] run: Convert all environment variables into bwrap
arguments
This avoids some of them being filtered out by a setuid bwrap. It also
means that if they came from an untrusted source, they cannot be used
to inject arbitrary code into a non-setuid bwrap via mechanisms like
LD_PRELOAD.
Because they get bundled into a memfd or temporary file, they do not
actually appear in argv, ensuring that they remain inaccessible to
processes running under a different uid (which is important if their
values are tokens or other secrets).
Signed-off-by: Simon McVittie <smcv@collabora.com>
Part-of: https://github.com/flatpak/flatpak/security/advisories/GHSA-4ppf-fxf6-vxg2
---
common/flatpak-bwrap-private.h | 3 +++
common/flatpak-bwrap.c | 43 ++++++++++++++++++++++++++++++++++
common/flatpak-run.c | 32 +++++++++++--------------
3 files changed, 60 insertions(+), 18 deletions(-)
diff --git a/common/flatpak-bwrap-private.h b/common/flatpak-bwrap-private.h
index 92d6e9de..6c31b789 100644
--- a/common/flatpak-bwrap-private.h
+++ b/common/flatpak-bwrap-private.h
@@ -43,6 +43,8 @@ void flatpak_bwrap_unset_env (FlatpakBwrap *bwrap,
const char *variable);
void flatpak_bwrap_add_arg (FlatpakBwrap *bwrap,
const char *arg);
+void flatpak_bwrap_take_arg (FlatpakBwrap *bwrap,
+ char *arg);
void flatpak_bwrap_add_noinherit_fd (FlatpakBwrap *bwrap,
int fd);
void flatpak_bwrap_add_fd (FlatpakBwrap *bwrap,
@@ -73,6 +75,7 @@ void flatpak_bwrap_add_bind_arg (FlatpakBwrap *bwrap,
const char *type,
const char *src,
const char *dest);
+void flatpak_bwrap_envp_to_args (FlatpakBwrap *bwrap);
gboolean flatpak_bwrap_bundle_args (FlatpakBwrap *bwrap,
int start,
int end,
diff --git a/common/flatpak-bwrap.c b/common/flatpak-bwrap.c
index 7e5d38d1..d383d25f 100644
--- a/common/flatpak-bwrap.c
+++ b/common/flatpak-bwrap.c
@@ -109,6 +109,18 @@ flatpak_bwrap_add_arg (FlatpakBwrap *bwrap, const char *arg)
g_ptr_array_add (bwrap->argv, g_strdup (arg));
}
+/*
+ * flatpak_bwrap_take_arg:
+ * @arg: (transfer full): Take ownership of this argument
+ *
+ * Add @arg to @bwrap's argv, taking ownership of the pointer.
+ */
+void
+flatpak_bwrap_take_arg (FlatpakBwrap *bwrap, char *arg)
+{
+ g_ptr_array_add (bwrap->argv, arg);
+}
+
void
flatpak_bwrap_finish (FlatpakBwrap *bwrap)
{
@@ -274,6 +286,37 @@ flatpak_bwrap_add_bind_arg (FlatpakBwrap *bwrap,
}
}
+/*
+ * Convert bwrap->envp into a series of --setenv arguments for bwrap(1),
+ * assumed to be applied to an empty environment. Reset envp to be an
+ * empty environment.
+ */
+void
+flatpak_bwrap_envp_to_args (FlatpakBwrap *bwrap)
+{
+ gsize i;
+
+ for (i = 0; bwrap->envp[i] != NULL; i++)
+ {
+ char *key_val = bwrap->envp[i];
+ char *eq = strchr (key_val, '=');
+
+ if (eq)
+ {
+ flatpak_bwrap_add_arg (bwrap, "--setenv");
+ flatpak_bwrap_take_arg (bwrap, g_strndup (key_val, eq - key_val));
+ flatpak_bwrap_add_arg (bwrap, eq + 1);
+ }
+ else
+ {
+ g_warn_if_reached ();
+ }
+ }
+
+ g_strfreev (g_steal_pointer (&bwrap->envp));
+ bwrap->envp = g_strdupv (flatpak_bwrap_empty_env);
+}
+
gboolean
flatpak_bwrap_bundle_args (FlatpakBwrap *bwrap,
int start,
diff --git a/common/flatpak-run.c b/common/flatpak-run.c
index 51c002ff..9383610b 100644
--- a/common/flatpak-run.c
+++ b/common/flatpak-run.c
@@ -1314,24 +1314,6 @@ flatpak_run_add_environment_args (FlatpakBwrap *bwrap,
flatpak_run_add_system_dbus_args (bwrap, proxy_arg_bwrap, context, flags);
flatpak_run_add_a11y_dbus_args (bwrap, proxy_arg_bwrap, context, flags);
- if (g_environ_getenv (bwrap->envp, "LD_LIBRARY_PATH") != NULL)
- {
- /* LD_LIBRARY_PATH is overridden for setuid helper, so pass it as cmdline arg */
- flatpak_bwrap_add_args (bwrap,
- "--setenv", "LD_LIBRARY_PATH", g_environ_getenv (bwrap->envp, "LD_LIBRARY_PATH"),
- NULL);
- flatpak_bwrap_unset_env (bwrap, "LD_LIBRARY_PATH");
- }
-
- if (g_environ_getenv (bwrap->envp, "TMPDIR") != NULL)
- {
- /* TMPDIR is overridden for setuid helper, so pass it as cmdline arg */
- flatpak_bwrap_add_args (bwrap,
- "--setenv", "TMPDIR", g_environ_getenv (bwrap->envp, "TMPDIR"),
- NULL);
- flatpak_bwrap_unset_env (bwrap, "TMPDIR");
- }
-
/* Must run this before spawning the dbus proxy, to ensure it
ends up in the app cgroup */
if (!flatpak_run_in_transient_unit (app_id, &my_error))
@@ -3852,6 +3834,8 @@ flatpak_run_app (const char *app_ref,
command = default_command;
}
+ flatpak_bwrap_envp_to_args (bwrap);
+
if (!flatpak_bwrap_bundle_args (bwrap, 1, -1, FALSE, error))
return FALSE;
@@ -3882,6 +3866,12 @@ flatpak_run_app (const char *app_ref,
/* We use LEAVE_DESCRIPTORS_OPEN to work around dead-lock, see flatpak_close_fds_workaround */
spawn_flags |= G_SPAWN_LEAVE_DESCRIPTORS_OPEN;
+ /* flatpak_bwrap_envp_to_args() moved the environment variables to
+ * be set into --setenv instructions in argv, so the environment
+ * in which the bwrap command runs must be empty. */
+ g_assert (bwrap->envp != NULL);
+ g_assert (bwrap->envp[0] == NULL);
+
if (!g_spawn_async (NULL,
(char **) bwrap->argv->pdata,
bwrap->envp,
@@ -3909,6 +3899,12 @@ flatpak_run_app (const char *app_ref,
* we do want to allow inheriting fds into flatpak run. */
flatpak_bwrap_child_setup (bwrap->fds, FALSE);
+ /* flatpak_bwrap_envp_to_args() moved the environment variables to
+ * be set into --setenv instructions in argv, so the environment
+ * in which the bwrap command runs must be empty. */
+ g_assert (bwrap->envp != NULL);
+ g_assert (bwrap->envp[0] == NULL);
+
if (execvpe (flatpak_get_bwrap (), (char **) bwrap->argv->pdata, bwrap->envp) == -1)
{
g_set_error_literal (error, G_IO_ERROR, g_io_error_from_errno (errno),
--
2.29.2
From a1dec4885218f40b03044c82245d5b362c0affeb Mon Sep 17 00:00:00 2001
From: Simon McVittie <smcv@collabora.com>
Date: Mon, 11 Jan 2021 12:14:48 +0000
Subject: [PATCH 03/10] tests: Expand coverage for environment variable
overrides
This checks that `flatpak run --env=` takes precedence over
`flatpak override --env=`, and that environment variables don't get
onto the bwrap command-line (which would be information disclosure
if their values are secret).
Signed-off-by: Simon McVittie <smcv@collabora.com>
Part-of: https://github.com/flatpak/flatpak/security/advisories/GHSA-4ppf-fxf6-vxg2
---
tests/test-override.sh | 68 +++++++++++++++++++++++++++++++++++++++++-
1 file changed, 67 insertions(+), 1 deletion(-)
diff --git a/tests/test-override.sh b/tests/test-override.sh
index 93009ee3..1213bbd4 100755
--- a/tests/test-override.sh
+++ b/tests/test-override.sh
@@ -12,7 +12,7 @@ reset_overrides () {
assert_file_empty info
}
-echo "1..13"
+echo "1..15"
setup_repo
install_repo
@@ -65,14 +65,80 @@ reset_overrides
${FLATPAK} override --user --env=FOO=BAR org.test.Hello
${FLATPAK} override --user --env=BAR= org.test.Hello
+# TODO: A future commit will add a way to avoid this ever being present in argv
+${FLATPAK} override --user --env=SECRET_TOKEN=3047225e-5e38-4357-b21c-eac83b7e8ea6 org.test.Hello
+# TMPDIR and TZDIR are filtered out by ld.so for setuid processes,
+# so setting these gives us a way to verify that we can pass them through
+# a setuid bwrap (without special-casing them, as we previously did for
+# TMPDIR).
+${FLATPAK} override --user --env=TMPDIR=/nonexistent/tmp org.test.Hello
+${FLATPAK} override --user --env=TZDIR=/nonexistent/tz org.test.Hello
${FLATPAK} override --user --show org.test.Hello > override
assert_file_has_content override "^\[Environment\]$"
assert_file_has_content override "^FOO=BAR$"
assert_file_has_content override "^BAR=$"
+assert_file_has_content override "^SECRET_TOKEN=3047225e-5e38-4357-b21c-eac83b7e8ea6$"
+assert_file_has_content override "^TMPDIR=/nonexistent/tmp$"
+assert_file_has_content override "^TZDIR=/nonexistent/tz$"
echo "ok override --env"
+if skip_one_without_bwrap "sandbox environment variables"; then
+ :
+else
+ ${FLATPAK} run --command=bash org.test.Hello \
+ -c 'echo "FOO=$FOO"; echo "BAR=$BAR"; echo "SECRET_TOKEN=$SECRET_TOKEN"; echo "TMPDIR=$TMPDIR"; echo "TZDIR=$TZDIR"' > out
+ assert_file_has_content out '^FOO=BAR$'
+ assert_file_has_content out '^BAR=$'
+ assert_file_has_content out '^SECRET_TOKEN=3047225e-5e38-4357-b21c-eac83b7e8ea6$'
+ # The variables that would be filtered out by a setuid bwrap get set
+ assert_file_has_content out '^TZDIR=/nonexistent/tz$'
+ assert_file_has_content out '^TMPDIR=/nonexistent/tmp$'
+ ${FLATPAK} run --command=cat org.test.Hello -- /proc/1/cmdline > out
+ # The secret doesn't end up in bubblewrap's cmdline where other users
+ # could see it
+ assert_not_file_has_content out 3047225e-5e38-4357-b21c-eac83b7e8ea6
+
+ ok "sandbox environment variables"
+fi
+
+reset_overrides
+
+if skip_one_without_bwrap "temporary environment variables"; then
+ :
+else
+ ${FLATPAK} override --user --env=FOO=wrong org.test.Hello
+ ${FLATPAK} override --user --env=BAR=wrong org.test.Hello
+ ${FLATPAK} override --user --env=SECRET_TOKEN=wrong org.test.Hello
+ ${FLATPAK} override --user --env=TMPDIR=/nonexistent/wrong org.test.Hello
+ ${FLATPAK} override --user --env=TZDIR=/nonexistent/wrong org.test.Hello
+ ${FLATPAK} override --user --show org.test.Hello > override
+
+ ${FLATPAK} run --command=bash \
+ --env=FOO=BAR \
+ --env=BAR= \
+ --env=SECRET_TOKEN=3047225e-5e38-4357-b21c-eac83b7e8ea6 \
+ --env=TMPDIR=/nonexistent/tmp \
+ --env=TZDIR=/nonexistent/tz \
+ org.test.Hello \
+ -c 'echo "FOO=$FOO"; echo "BAR=$BAR"; echo "SECRET_TOKEN=$SECRET_TOKEN"; echo "TMPDIR=$TMPDIR"; echo "TZDIR=$TZDIR"' > out
+ # The versions from `flatpak run` overrule `flatpak override`
+ assert_file_has_content out '^FOO=BAR$'
+ assert_file_has_content out '^BAR=$'
+ assert_file_has_content out '^SECRET_TOKEN=3047225e-5e38-4357-b21c-eac83b7e8ea6$'
+ assert_file_has_content out '^TZDIR=/nonexistent/tz$'
+ assert_file_has_content out '^TMPDIR=/nonexistent/tmp$'
+ ${FLATPAK} run --command=cat org.test.Hello -- /proc/1/cmdline > out
+ # The secret doesn't end up in bubblewrap's cmdline where other users
+ # could see it
+ assert_not_file_has_content out 3047225e-5e38-4357-b21c-eac83b7e8ea6
+
+ ok "temporary environment variables"
+fi
+
+reset_overrides
+
${FLATPAK} override --user --filesystem=home org.test.Hello
${FLATPAK} override --user --filesystem=xdg-desktop/foo:create org.test.Hello
${FLATPAK} override --user --filesystem=xdg-config:ro org.test.Hello
--
2.29.2
From 1b80c139f02cff6eeec39ecdf1a8f531ab6d7d9b Mon Sep 17 00:00:00 2001
From: Simon McVittie <smcv@collabora.com>
Date: Sun, 10 Jan 2021 16:18:58 +0000
Subject: [PATCH 04/10] context: Add --env-fd option
This allows environment variables to be added to the context without
making their values visible to processes running under a different uid,
which might be significant if the variable's value is a token or some
other secret value.
Signed-off-by: Simon McVittie <smcv@collabora.com>
Part-of: https://github.com/flatpak/flatpak/security/advisories/GHSA-4ppf-fxf6-vxg2
---
common/flatpak-context.c | 60 ++++++++++++++++++++++++++++++++++++
doc/flatpak-build-finish.xml | 18 +++++++++++
doc/flatpak-build.xml | 18 +++++++++++
doc/flatpak-override.xml | 18 +++++++++++
doc/flatpak-run.xml | 18 +++++++++++
5 files changed, 132 insertions(+)
diff --git a/common/flatpak-context.c b/common/flatpak-context.c
index 462134aa..7e1bc46c 100644
--- a/common/flatpak-context.c
+++ b/common/flatpak-context.c
@@ -1039,6 +1039,65 @@ option_env_cb (const gchar *option_name,
return TRUE;
}
+static gboolean
+option_env_fd_cb (const gchar *option_name,
+ const gchar *value,
+ gpointer data,
+ GError **error)
+{
+ FlatpakContext *context = data;
+ g_autoptr(GBytes) env_block = NULL;
+ gsize remaining;
+ const char *p;
+ guint64 fd;
+ gchar *endptr;
+
+ fd = g_ascii_strtoull (value, &endptr, 10);
+
+ if (endptr == NULL || *endptr != '\0' || fd > G_MAXINT)
+ return glnx_throw (error, "Not a valid file descriptor: %s", value);
+
+ env_block = glnx_fd_readall_bytes ((int) fd, NULL, error);
+
+ if (env_block == NULL)
+ return FALSE;
+
+ p = g_bytes_get_data (env_block, &remaining);
+
+ /* env_block might not be \0-terminated */
+ while (remaining > 0)
+ {
+ size_t len = strnlen (p, remaining);
+ const char *equals;
+
+ g_assert (len <= remaining);
+
+ equals = memchr (p, '=', len);
+
+ if (equals == NULL || equals == p)
+ return glnx_throw (error,
+ "Environment variable must be given in the form VARIABLE=VALUE, not %.*s", (int) len, p);
+
+ flatpak_context_set_env_var (context,
+ g_strndup (p, equals - p),
+ g_strndup (equals + 1, len - (equals - p) - 1));
+ p += len;
+ remaining -= len;
+
+ if (remaining > 0)
+ {
+ g_assert (*p == '\0');
+ p += 1;
+ remaining -= 1;
+ }
+ }
+
+ if (fd >= 3)
+ close (fd);
+
+ return TRUE;
+}
+
static gboolean
option_own_name_cb (const gchar *option_name,
const gchar *value,
@@ -1236,6 +1295,7 @@ static GOptionEntry context_options[] = {
{ "filesystem", 0, G_OPTION_FLAG_IN_MAIN, G_OPTION_ARG_CALLBACK, &option_filesystem_cb, N_("Expose filesystem to app (:ro for read-only)"), N_("FILESYSTEM[:ro]") },
{ "nofilesystem", 0, G_OPTION_FLAG_IN_MAIN, G_OPTION_ARG_CALLBACK, &option_nofilesystem_cb, N_("Don't expose filesystem to app"), N_("FILESYSTEM") },
{ "env", 0, G_OPTION_FLAG_IN_MAIN, G_OPTION_ARG_CALLBACK, &option_env_cb, N_("Set environment variable"), N_("VAR=VALUE") },
+ { "env-fd", 0, G_OPTION_FLAG_IN_MAIN, G_OPTION_ARG_CALLBACK, &option_env_fd_cb, N_("Read environment variables in env -0 format from FD"), N_("FD") },
{ "own-name", 0, G_OPTION_FLAG_IN_MAIN, G_OPTION_ARG_CALLBACK, &option_own_name_cb, N_("Allow app to own name on the session bus"), N_("DBUS_NAME") },
{ "talk-name", 0, G_OPTION_FLAG_IN_MAIN, G_OPTION_ARG_CALLBACK, &option_talk_name_cb, N_("Allow app to talk to name on the session bus"), N_("DBUS_NAME") },
{ "no-talk-name", 0, G_OPTION_FLAG_IN_MAIN, G_OPTION_ARG_CALLBACK, &option_no_talk_name_cb, N_("Don't allow app to talk to name on the session bus"), N_("DBUS_NAME") },
diff --git a/doc/flatpak-build-finish.xml b/doc/flatpak-build-finish.xml
index d92eeb4d..2e01cd3e 100644
--- a/doc/flatpak-build-finish.xml
+++ b/doc/flatpak-build-finish.xml
@@ -286,6 +286,24 @@ key=v1;v2;
</para></listitem>
</varlistentry>
+ <varlistentry>
+ <term><option>--env-fd=<replaceable>FD</replaceable></option></term>
+
+ <listitem><para>
+ Read environment variables from the file descriptor
+ <replaceable>FD</replaceable>, and set them as if
+ via <option>--env</option>. This can be used to avoid
+ environment variables and their values becoming visible
+ to other users.
+ </para><para>
+ Each environment variable is in the form
+ <replaceable>VAR</replaceable>=<replaceable>VALUE</replaceable>
+ followed by a zero byte. This is the same format used by
+ <literal>env -0</literal> and
+ <filename>/proc/*/environ</filename>.
+ </para></listitem>
+ </varlistentry>
+
<varlistentry>
<term><option>--own-name=NAME</option></term>
diff --git a/doc/flatpak-build.xml b/doc/flatpak-build.xml
index 55e3ec89..e3eb9bc8 100644
--- a/doc/flatpak-build.xml
+++ b/doc/flatpak-build.xml
@@ -288,6 +288,24 @@ key=v1;v2;
</para></listitem>
</varlistentry>
+ <varlistentry>
+ <term><option>--env-fd=<replaceable>FD</replaceable></option></term>
+
+ <listitem><para>
+ Read environment variables from the file descriptor
+ <replaceable>FD</replaceable>, and set them as if
+ via <option>--env</option>. This can be used to avoid
+ environment variables and their values becoming visible
+ to other users.
+ </para><para>
+ Each environment variable is in the form
+ <replaceable>VAR</replaceable>=<replaceable>VALUE</replaceable>
+ followed by a zero byte. This is the same format used by
+ <literal>env -0</literal> and
+ <filename>/proc/*/environ</filename>.
+ </para></listitem>
+ </varlistentry>
+
<varlistentry>
<term><option>--own-name=NAME</option></term>
diff --git a/doc/flatpak-override.xml b/doc/flatpak-override.xml
index 8f131575..137e1251 100644
--- a/doc/flatpak-override.xml
+++ b/doc/flatpak-override.xml
@@ -262,6 +262,24 @@ key=v1;v2;
</para></listitem>
</varlistentry>
+ <varlistentry>
+ <term><option>--env-fd=<replaceable>FD</replaceable></option></term>
+
+ <listitem><para>
+ Read environment variables from the file descriptor
+ <replaceable>FD</replaceable>, and set them as if
+ via <option>--env</option>. This can be used to avoid
+ environment variables and their values becoming visible
+ to other users.
+ </para><para>
+ Each environment variable is in the form
+ <replaceable>VAR</replaceable>=<replaceable>VALUE</replaceable>
+ followed by a zero byte. This is the same format used by
+ <literal>env -0</literal> and
+ <filename>/proc/*/environ</filename>.
+ </para></listitem>
+ </varlistentry>
+
<varlistentry>
<term><option>--own-name=NAME</option></term>
diff --git a/doc/flatpak-run.xml b/doc/flatpak-run.xml
index 5077c1a9..ed157341 100644
--- a/doc/flatpak-run.xml
+++ b/doc/flatpak-run.xml
@@ -402,6 +402,24 @@ key=v1;v2;
</para></listitem>
</varlistentry>
+ <varlistentry>
+ <term><option>--env-fd=<replaceable>FD</replaceable></option></term>
+
+ <listitem><para>
+ Read environment variables from the file descriptor
+ <replaceable>FD</replaceable>, and set them as if
+ via <option>--env</option>. This can be used to avoid
+ environment variables and their values becoming visible
+ to other users.
+ </para><para>
+ Each environment variable is in the form
+ <replaceable>VAR</replaceable>=<replaceable>VALUE</replaceable>
+ followed by a zero byte. This is the same format used by
+ <literal>env -0</literal> and
+ <filename>/proc/*/environ</filename>.
+ </para></listitem>
+ </varlistentry>
+
<varlistentry>
<term><option>--own-name=NAME</option></term>
--
2.29.2
From 6c244791c912fe0c5ae2e140f251dc02c46cc0aa Mon Sep 17 00:00:00 2001
From: Simon McVittie <smcv@collabora.com>
Date: Tue, 12 Jan 2021 10:11:51 +0000
Subject: [PATCH 05/10] portal: Convert --env in extra-args into --env-fd
This hides overridden variables from the command-line, which means
processes running under other uids can't see them in /proc/*/cmdline,
which might be important if they contain secrets.
Signed-off-by: Simon McVittie <smcv@collabora.com>
Part-of: https://github.com/flatpak/flatpak/security/advisories/GHSA-4ppf-fxf6-vxg2
---
portal/flatpak-portal.c | 51 ++++++++++++++++++++++++++++++++++++++++-
1 file changed, 50 insertions(+), 1 deletion(-)
diff --git a/portal/flatpak-portal.c b/portal/flatpak-portal.c
index 060987b7..03ea58cc 100644
--- a/portal/flatpak-portal.c
+++ b/portal/flatpak-portal.c
@@ -249,6 +249,7 @@ typedef struct
int fd_map_len;
gboolean set_tty;
int tty;
+ int env_fd;
} ChildSetupData;
static void
@@ -267,6 +268,9 @@ child_setup_func (gpointer user_data)
flatpak_close_fds_workaround (3);
+ if (data->env_fd != -1)
+ drop_cloexec (data->env_fd);
+
/* Unblock all signals */
sigemptyset (&set);
if (pthread_sigmask (SIG_SETMASK, &set, NULL) == -1)
@@ -553,6 +557,9 @@ handle_spawn (PortalFlatpak *object,
gboolean sandboxed;
gboolean devel;
gboolean expose_pids;
+ g_autoptr(GString) env_string = g_string_new ("");
+
+ child_setup_data.env_fd = -1;
if (fd_list != NULL)
fds = g_unix_fd_list_peek_fds (fd_list, &fds_len);
@@ -805,7 +812,49 @@ handle_spawn (PortalFlatpak *object,
else
{
for (i = 0; extra_args != NULL && extra_args[i] != NULL; i++)
- g_ptr_array_add (flatpak_argv, g_strdup (extra_args[i]));
+ {
+ if (g_str_has_prefix (extra_args[i], "--env="))
+ {
+ const char *var_val = extra_args[i] + strlen ("--env=");
+
+ if (var_val[0] == '\0' || var_val[0] == '=')
+ {
+ g_warning ("Environment variable in extra-args has empty name");
+ continue;
+ }
+
+ if (strchr (var_val, '=') == NULL)
+ {
+ g_warning ("Environment variable in extra-args has no value");
+ continue;
+ }
+
+ g_string_append (env_string, var_val);
+ g_string_append_c (env_string, '\0');
+ }
+ else
+ {
+ g_ptr_array_add (flatpak_argv, g_strdup (extra_args[i]));
+ }
+ }
+ }
+
+ if (env_string->len > 0)
+ {
+ g_auto(GLnxTmpfile) env_tmpf = { 0, };
+
+ if (!flatpak_buffer_to_sealed_memfd_or_tmpfile (&env_tmpf, "environ",
+ env_string->str,
+ env_string->len, &error))
+ {
+ g_dbus_method_invocation_return_gerror (invocation, error);
+ return G_DBUS_METHOD_INVOCATION_HANDLED;
+ }
+
+ child_setup_data.env_fd = glnx_steal_fd (&env_tmpf.fd);
+ g_ptr_array_add (flatpak_argv,
+ g_strdup_printf ("--env-fd=%d",
+ child_setup_data.env_fd));
}
expose_pids = (arg_flags & FLATPAK_SPAWN_FLAGS_EXPOSE_PIDS) != 0;
--
2.29.2
From f1725cd4fc6164d33f7a92bba673e8718655c1f1 Mon Sep 17 00:00:00 2001
From: Simon McVittie <smcv@collabora.com>
Date: Mon, 11 Jan 2021 12:25:50 +0000
Subject: [PATCH 06/10] tests: Exercise --env-fd
Signed-off-by: Simon McVittie <smcv@collabora.com>
Part-of: https://github.com/flatpak/flatpak/security/advisories/GHSA-4ppf-fxf6-vxg2
---
tests/test-override.sh | 18 ++++++++++--------
1 file changed, 10 insertions(+), 8 deletions(-)
diff --git a/tests/test-override.sh b/tests/test-override.sh
index 1213bbd4..1c7dafd3 100755
--- a/tests/test-override.sh
+++ b/tests/test-override.sh
@@ -65,14 +65,16 @@ reset_overrides
${FLATPAK} override --user --env=FOO=BAR org.test.Hello
${FLATPAK} override --user --env=BAR= org.test.Hello
-# TODO: A future commit will add a way to avoid this ever being present in argv
-${FLATPAK} override --user --env=SECRET_TOKEN=3047225e-5e38-4357-b21c-eac83b7e8ea6 org.test.Hello
+# --env-fd with terminating \0 (strictly as documented).
+printf '%s\0' "SECRET_TOKEN=3047225e-5e38-4357-b21c-eac83b7e8ea6" > env.3
+# --env-fd without terminating \0 (which we also accept).
# TMPDIR and TZDIR are filtered out by ld.so for setuid processes,
# so setting these gives us a way to verify that we can pass them through
# a setuid bwrap (without special-casing them, as we previously did for
# TMPDIR).
-${FLATPAK} override --user --env=TMPDIR=/nonexistent/tmp org.test.Hello
-${FLATPAK} override --user --env=TZDIR=/nonexistent/tz org.test.Hello
+printf '%s\0%s' "TMPDIR=/nonexistent/tmp" "TZDIR=/nonexistent/tz" > env.4
+${FLATPAK} override --user --env-fd=3 --env-fd=4 org.test.Hello \
+ 3<env.3 4<env.4
${FLATPAK} override --user --show org.test.Hello > override
assert_file_has_content override "^\[Environment\]$"
@@ -118,11 +120,11 @@ else
${FLATPAK} run --command=bash \
--env=FOO=BAR \
--env=BAR= \
- --env=SECRET_TOKEN=3047225e-5e38-4357-b21c-eac83b7e8ea6 \
- --env=TMPDIR=/nonexistent/tmp \
- --env=TZDIR=/nonexistent/tz \
+ --env-fd=3 \
+ --env-fd=4 \
org.test.Hello \
- -c 'echo "FOO=$FOO"; echo "BAR=$BAR"; echo "SECRET_TOKEN=$SECRET_TOKEN"; echo "TMPDIR=$TMPDIR"; echo "TZDIR=$TZDIR"' > out
+ -c 'echo "FOO=$FOO"; echo "BAR=$BAR"; echo "SECRET_TOKEN=$SECRET_TOKEN"; echo "TMPDIR=$TMPDIR"; echo "TZDIR=$TZDIR"' \
+ 3<env.3 4<env.4 > out
# The versions from `flatpak run` overrule `flatpak override`
assert_file_has_content out '^FOO=BAR$'
assert_file_has_content out '^BAR=$'
--
2.29.2
From adcb3b2608caa1ab6647f59e31a9084ec0b66bbb Mon Sep 17 00:00:00 2001
From: Simon McVittie <smcv@collabora.com>
Date: Sun, 10 Jan 2021 16:25:29 +0000
Subject: [PATCH 07/10] portal: Do not use caller-supplied variables in
environment
If the caller specifies a variable that can be used to inject arbitrary
code into processes, we must not allow it to enter the environment
block used to run `flatpak run`, which runs unsandboxed.
This change requires the previous commit "context: Add --env-fd option",
which adds infrastructure used here.
To be secure, this change also requires the previous commit
"run: Convert all environment variables into bwrap arguments", which
protects a non-setuid bwrap(1) from the same attack.
Signed-off-by: Simon McVittie <smcv@collabora.com>
Part-of: https://github.com/flatpak/flatpak/security/advisories/GHSA-4ppf-fxf6-vxg2
---
portal/flatpak-portal.c | 28 +++++++++++++++++++++++++++-
1 file changed, 27 insertions(+), 1 deletion(-)
diff --git a/portal/flatpak-portal.c b/portal/flatpak-portal.c
index 03ea58cc..fe8a514f 100644
--- a/portal/flatpak-portal.c
+++ b/portal/flatpak-portal.c
@@ -760,6 +760,13 @@ handle_spawn (PortalFlatpak *object,
else
env = g_get_environ ();
+ /* Let the environment variables given by the caller override the ones
+ * from extra_args. Don't add them to @env, because they are controlled
+ * by our caller, which might be trying to use them to inject code into
+ * flatpak(1); add them to the environment block instead.
+ *
+ * We don't use --env= here, so that if the values are something that
+ * should not be exposed to other uids, they can remain confidential. */
n_envs = g_variant_n_children (arg_envs);
for (i = 0; i < n_envs; i++)
{
@@ -767,7 +774,26 @@ handle_spawn (PortalFlatpak *object,
const char *val = NULL;
g_variant_get_child (arg_envs, i, "{&s&s}", &var, &val);
- env = g_environ_setenv (env, var, val, TRUE);
+ if (var[0] == '\0')
+ {
+ g_dbus_method_invocation_return_error (invocation, G_DBUS_ERROR,
+ G_DBUS_ERROR_INVALID_ARGS,
+ "Environment variable cannot have empty name");
+ return G_DBUS_METHOD_INVOCATION_HANDLED;
+ }
+
+ if (strchr (var, '=') != NULL)
+ {
+ g_dbus_method_invocation_return_error (invocation, G_DBUS_ERROR,
+ G_DBUS_ERROR_INVALID_ARGS,
+ "Environment variable name cannot contain '='");
+ return G_DBUS_METHOD_INVOCATION_HANDLED;
+ }
+
+ g_string_append (env_string, var);
+ g_string_append_c (env_string, '=');
+ g_string_append (env_string, val);
+ g_string_append_c (env_string, '\0');
}
g_ptr_array_add (flatpak_argv, g_strdup ("flatpak"));
--
2.29.2
From 1fb13b40cea72ded0ca804a990e84b12454a30a1 Mon Sep 17 00:00:00 2001
From: Simon McVittie <smcv@collabora.com>
Date: Mon, 11 Jan 2021 12:48:01 +0000
Subject: [PATCH 08/10] tests: Assert that --env= does not go in `flatpak run`
or bwrap environ
For the portal's use of --env-fd= to be safe, we want the environment
variables that it sets to end up in the environment for the program
that is run by `bwrap` as process 2, but they must not go into the
environment that gets used to run `flatpak run` or `bwrap`. Assert
that this is the case.
For completeness, we're testing both --env= and --env-fd= here,
even though the earlier commit
"portal: Do not use caller-supplied variables in environment"
always uses --env-fd=.
Part-of: https://github.com/flatpak/flatpak/security/advisories/GHSA-4ppf-fxf6-vxg2
Signed-off-by: Simon McVittie <smcv@collabora.com>
---
tests/Makefile.am.inc | 10 ++++++++++
tests/libpreload.c | 31 +++++++++++++++++++++++++++++++
tests/test-override.sh | 18 ++++++++++++++++++
3 files changed, 59 insertions(+)
create mode 100644 tests/libpreload.c
diff --git a/tests/Makefile.am.inc b/tests/Makefile.am.inc
index 15f52148..c95ed3bc 100644
--- a/tests/Makefile.am.inc
+++ b/tests/Makefile.am.inc
@@ -156,6 +156,16 @@ dist_installed_test_data = \
tests/org.flatpak.Authenticator.test.service.in \
$(NULL)
+test_ltlibraries = tests/libpreload.la
+
+tests_libpreload_la_SOURCES = tests/libpreload.c
+tests_libpreload_la_LDFLAGS = \
+ -avoid-version \
+ -module \
+ -no-undefined \
+ -rpath $(installed_testdir) \
+ $(NULL)
+
installed_test_keyringdir = $(installed_testdir)/test-keyring
installed_test_keyring2dir = $(installed_testdir)/test-keyring2
diff --git a/tests/libpreload.c b/tests/libpreload.c
new file mode 100644
index 00000000..a640a945
--- /dev/null
+++ b/tests/libpreload.c
@@ -0,0 +1,31 @@
+/*
+ * Copyright 2021 Collabora Ltd.
+ * SPDX-License-Identifier: LGPL-2-or-later
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+__attribute__((constructor)) static void
+ctor (void)
+{
+ pid_t me = getpid ();
+ struct stat buf;
+
+ fprintf (stderr, "LD_PRELOAD module got loaded by process %d\n", me);
+
+ if (stat ("/.flatpak-info", &buf) == 0)
+ {
+ fprintf (stderr, "OK: pid %d is in a Flatpak sandbox\n", me);
+ }
+ else
+ {
+ /* If the --env=LD_PRELOAD had come from a call to flatpak-portal,
+ * then this would be a sandbox escape (GHSA-4ppf-fxf6-vxg2). */
+ fprintf (stderr, "Error: pid %d is not in a Flatpak sandbox\n", me);
+ abort ();
+ }
+}
diff --git a/tests/test-override.sh b/tests/test-override.sh
index 1c7dafd3..47416a6d 100755
--- a/tests/test-override.sh
+++ b/tests/test-override.sh
@@ -3,6 +3,11 @@
set -euo pipefail
. $(dirname $0)/libtest.sh
+if [ -e "${test_builddir}/.libs/libpreload.so" ]; then
+ install "${test_builddir}/.libs/libpreload.so" "${test_tmpdir}"
+else
+ install "${test_builddir}/libpreload.so" "${test_tmpdir}"
+fi
skip_revokefs_without_fuse
@@ -118,6 +123,7 @@ else
${FLATPAK} override --user --show org.test.Hello > override
${FLATPAK} run --command=bash \
+ --filesystem="${test_tmpdir}" \
--env=FOO=BAR \
--env=BAR= \
--env-fd=3 \
@@ -136,6 +142,18 @@ else
# could see it
assert_not_file_has_content out 3047225e-5e38-4357-b21c-eac83b7e8ea6
+ # libpreload.so will abort() if it gets loaded into the `flatpak run`
+ # or `bwrap` processes, so if this succeeds, everything's OK
+ ${FLATPAK} run --command=bash \
+ --filesystem="${test_tmpdir}" \
+ --env=LD_PRELOAD="${test_tmpdir}/libpreload.so" \
+ org.test.Hello -c ''
+ printf '%s\0' "LD_PRELOAD=${test_tmpdir}/libpreload.so" > env.ldpreload
+ ${FLATPAK} run --command=bash \
+ --filesystem="${test_tmpdir}" \
+ --env-fd=3 \
+ org.test.Hello -c '' 3<env.ldpreload
+
ok "temporary environment variables"
fi
--
2.29.2
From e4a3720e49aa38d0ed07106663499f957c070847 Mon Sep 17 00:00:00 2001
From: Simon McVittie <smcv@collabora.com>
Date: Mon, 18 Jan 2021 17:52:13 +0000
Subject: [PATCH 09/10] build: Convert environment into a sequence of bwrap
arguments
This means we can systematically pass the environment variables
through bwrap(1), even if it is setuid and thus is filtering out
security-sensitive environment variables. bwrap itself ends up being
run with an empty environment instead.
This fixes a regression when CVE-2021-21261 was fixed: before the
CVE fixes, LD_LIBRARY_PATH would have been passed through like this
and appeared in the `flatpak build` shell, but during the CVE fixes,
the special case that protected LD_LIBRARY_PATH was removed in favour
of the more general flatpak_bwrap_envp_to_args(). That reasoning only
works if we use flatpak_bwrap_envp_to_args(), consistently, everywhere
that we run the potentially-setuid bwrap.
Fixes: 6d1773d2 "run: Convert all environment variables into bwrap arguments"
Resolves: https://github.com/flatpak/flatpak/issues/4080
Bug-Debian: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=980323
Signed-off-by: Simon McVittie <smcv@collabora.com>
---
app/flatpak-builtins-build.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/app/flatpak-builtins-build.c b/app/flatpak-builtins-build.c
index 5ecd2ef3..8616f3c8 100644
--- a/app/flatpak-builtins-build.c
+++ b/app/flatpak-builtins-build.c
@@ -569,6 +569,8 @@ flatpak_builtin_build (int argc, char **argv, GCancellable *cancellable, GError
NULL);
}
+ flatpak_bwrap_envp_to_args (bwrap);
+
if (!flatpak_bwrap_bundle_args (bwrap, 1, -1, FALSE, error))
return FALSE;
--
2.29.2
From f830b97e81a626a43b160ccb5dad4fe934ab03fa Mon Sep 17 00:00:00 2001
From: Simon McVittie <smcv@collabora.com>
Date: Mon, 18 Jan 2021 18:07:38 +0000
Subject: [PATCH 10/10] dir: Pass environment via bwrap --setenv when running
apply_extra
This means we can systematically pass the environment variables
through bwrap(1), even if it is setuid and thus is filtering out
security-sensitive environment variables. bwrap ends up being
run with an empty environment instead.
As with the previous commit, this regressed while fixing CVE-2021-21261.
Fixes: 6d1773d2 "run: Convert all environment variables into bwrap arguments"
Signed-off-by: Simon McVittie <smcv@collabora.com>
---
common/flatpak-dir.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/common/flatpak-dir.c b/common/flatpak-dir.c
index c3ab8bcf..030b8a31 100644
--- a/common/flatpak-dir.c
+++ b/common/flatpak-dir.c
@@ -7751,6 +7751,8 @@ apply_extra_data (FlatpakDir *self,
app_context, NULL, NULL, NULL, cancellable, error))
return FALSE;
+ flatpak_bwrap_envp_to_args (bwrap);
+
flatpak_bwrap_add_arg (bwrap, "/app/bin/apply_extra");
flatpak_bwrap_finish (bwrap);
--
2.29.2