You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
199 lines
9.6 KiB
199 lines
9.6 KiB
11 months ago
|
From 9c8a6018ed4a4da6efb1fc6958e70f9324bb5b1e Mon Sep 17 00:00:00 2001
|
||
|
|
From: =?UTF-8?q?Zbigniew=20J=C4=99drzejewski-Szmek?= <zbyszek@in.waw.pl>
|
||
|
|
Date: Wed, 7 Oct 2020 11:15:05 +0200
|
||
|
|
Subject: [PATCH] pager: make pager secure when under euid is changed or
|
||
|
|
explicitly requested
|
||
|
|
|
||
|
|
The variable is renamed to SYSTEMD_PAGERSECURE (because it's not just about
|
||
|
|
less now), and we automatically enable secure mode in certain cases, but not
|
||
|
|
otherwise.
|
||
|
|
|
||
|
|
This approach is more nuanced, but should provide a better experience for
|
||
|
|
users:
|
||
|
|
|
||
|
|
- Previusly we would set LESSSECURE=1 and trust the pager to make use of
|
||
|
|
it. But this has an effect only on less. We need to not start pagers which
|
||
|
|
are insecure when in secure mode. In particular more is like that and is a
|
||
|
|
very popular pager.
|
||
|
|
|
||
|
|
- We don't enable secure mode always, which means that those other pagers can
|
||
|
|
reasonably used.
|
||
|
|
|
||
|
|
- We do the right thing by default, but the user has ultimate control by
|
||
|
|
setting SYSTEMD_PAGERSECURE.
|
||
|
|
|
||
|
|
Fixes #5666.
|
||
|
|
|
||
|
|
v2:
|
||
|
|
- also check $PKEXEC_UID
|
||
|
|
|
||
|
|
v3:
|
||
|
|
- use 'sd_pid_get_owner_uid() != geteuid()' as the condition
|
||
|
|
|
||
|
|
(cherry picked from commit 0a42426d797406b4b01a0d9c13bb759c2629d108)
|
||
|
|
|
||
|
|
Resolves: #2175623
|
||
|
|
---
|
||
|
|
man/less-variables.xml | 28 ++++++++++++++---
|
||
|
|
meson.build | 3 +-
|
||
|
|
src/basic/pager.c | 69 +++++++++++++++++++++++++++---------------
|
||
|
|
3 files changed, 69 insertions(+), 31 deletions(-)
|
||
|
|
|
||
|
|
diff --git a/man/less-variables.xml b/man/less-variables.xml
|
||
|
|
index 9dad4247da..5f3a53c8dd 100644
|
||
|
|
--- a/man/less-variables.xml
|
||
|
|
+++ b/man/less-variables.xml
|
||
|
|
@@ -37,12 +37,30 @@
|
||
|
|
</varlistentry>
|
||
|
|
|
||
|
|
<varlistentry id='lesssecure'>
|
||
|
|
- <term><varname>$SYSTEMD_LESSSECURE</varname></term>
|
||
|
|
+ <term><varname>$SYSTEMD_PAGERSECURE</varname></term>
|
||
|
|
|
||
|
|
- <listitem><para>Takes a boolean argument. Overrides the <varname>$LESSSECURE</varname> environment
|
||
|
|
- variable when invoking the pager, which controls the "secure" mode of less (which disables commands
|
||
|
|
- such as <literal>|</literal> which allow to easily shell out to external command lines). By default
|
||
|
|
- less secure mode is enabled, with this setting it may be disabled.</para></listitem>
|
||
|
|
+ <listitem><para>Takes a boolean argument. When true, the "secure" mode of the pager is enabled; if
|
||
|
|
+ false, disabled. If <varname>$SYSTEMD_PAGERSECURE</varname> is not set at all, secure mode is enabled
|
||
|
|
+ if the effective UID is not the same as the owner of the login session, see <citerefentry
|
||
|
|
+ project='man-pages'><refentrytitle>geteuid</refentrytitle><manvolnum>2</manvolnum></citerefentry> and
|
||
|
|
+ <citerefentry><refentrytitle>sd_pid_get_owner_uid</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
|
||
|
|
+ In secure mode, <option>LESSSECURE=1</option> will be set when invoking the pager, and the pager shall
|
||
|
|
+ disable commands that open or create new files or start new subprocesses. When
|
||
|
|
+ <varname>$SYSTEMD_PAGERSECURE</varname> is not set at all, pagers which are not known to implement
|
||
|
|
+ secure mode will not be used. (Currently only
|
||
|
|
+ <citerefentry><refentrytitle>less</refentrytitle><manvolnum>1</manvolnum></citerefentry> implements
|
||
|
|
+ secure mode.)</para>
|
||
|
|
+
|
||
|
|
+ <para>Note: when commands are invoked with elevated privileges, for example under <citerefentry
|
||
|
|
+ project='man-pages'><refentrytitle>sudo</refentrytitle><manvolnum>8</manvolnum></citerefentry> or
|
||
|
|
+ <citerefentry
|
||
|
|
+ project='die-net'><refentrytitle>pkexec</refentrytitle><manvolnum>1</manvolnum></citerefentry>, care
|
||
|
|
+ must be taken to ensure that unintended interactive features are not enabled. "Secure" mode for the
|
||
|
|
+ pager may be enabled automatically as describe above. Setting <varname>SYSTEMD_PAGERSECURE=0</varname>
|
||
|
|
+ or not removing it from the inherited environment allows the user to invoke arbitrary commands. Note
|
||
|
|
+ that if the <varname>$SYSTEMD_PAGER</varname> or <varname>$PAGER</varname> variables are to be
|
||
|
|
+ honoured, <varname>$SYSTEMD_PAGERSECURE</varname> must be set too. It might be reasonable to completly
|
||
|
|
+ disable the pager using <option>--no-pager</option> instead.</para></listitem>
|
||
|
|
</varlistentry>
|
||
|
|
</variablelist>
|
||
|
|
</refsect1>
|
||
|
|
diff --git a/meson.build b/meson.build
|
||
|
|
index 673800a1a7..d986dd24ac 100644
|
||
|
|
--- a/meson.build
|
||
|
|
+++ b/meson.build
|
||
|
|
@@ -1467,7 +1467,8 @@ test_dlopen = executable(
|
||
|
|
'test-dlopen',
|
||
|
|
test_dlopen_c,
|
||
|
|
include_directories : includes,
|
||
|
|
- link_with : [libbasic],
|
||
|
|
+ link_with : [libsystemd_static,
|
||
|
|
+ libbasic],
|
||
|
|
dependencies : [libdl])
|
||
|
|
|
||
|
|
foreach tuple : [['myhostname', 'ENABLE_NSS_MYHOSTNAME'],
|
||
|
|
diff --git a/src/basic/pager.c b/src/basic/pager.c
|
||
|
|
index 4efb01c483..c7e101235d 100644
|
||
|
|
--- a/src/basic/pager.c
|
||
|
|
+++ b/src/basic/pager.c
|
||
|
|
@@ -10,6 +10,8 @@
|
||
|
|
#include <sys/prctl.h>
|
||
|
|
#include <unistd.h>
|
||
|
|
|
||
|
|
+#include "sd-login.h"
|
||
|
|
+
|
||
|
|
#include "copy.h"
|
||
|
|
#include "env-util.h"
|
||
|
|
#include "fd-util.h"
|
||
|
|
@@ -79,7 +81,7 @@ int pager_open(bool no_pager, bool jump_to_end) {
|
||
|
|
if (r < 0)
|
||
|
|
return r;
|
||
|
|
if (r == 0) {
|
||
|
|
- const char* less_opts, *less_charset;
|
||
|
|
+ const char* less_opts, *less_charset, *exe;
|
||
|
|
|
||
|
|
/* In the child start the pager */
|
||
|
|
|
||
|
|
@@ -105,39 +107,56 @@ int pager_open(bool no_pager, bool jump_to_end) {
|
||
|
|
_exit(EXIT_FAILURE);
|
||
|
|
|
||
|
|
/* People might invoke us from sudo, don't needlessly allow less to be a way to shell out
|
||
|
|
- * privileged stuff. */
|
||
|
|
- r = getenv_bool("SYSTEMD_LESSSECURE");
|
||
|
|
- if (r == 0) { /* Remove env var if off */
|
||
|
|
- if (unsetenv("LESSSECURE") < 0) {
|
||
|
|
- log_error_errno(errno, "Failed to uset environment variable LESSSECURE: %m");
|
||
|
|
- _exit(EXIT_FAILURE);
|
||
|
|
- }
|
||
|
|
- } else {
|
||
|
|
- /* Set env var otherwise */
|
||
|
|
+ * privileged stuff. If the user set $SYSTEMD_PAGERSECURE, trust their configuration of the
|
||
|
|
+ * pager. If they didn't, use secure mode when under euid is changed. If $SYSTEMD_PAGERSECURE
|
||
|
|
+ * wasn't explicitly set, and we autodetect the need for secure mode, only use the pager we
|
||
|
|
+ * know to be good. */
|
||
|
|
+ int use_secure_mode = getenv_bool("SYSTEMD_PAGERSECURE");
|
||
|
|
+ bool trust_pager = use_secure_mode >= 0;
|
||
|
|
+ if (use_secure_mode == -ENXIO) {
|
||
|
|
+ uid_t uid;
|
||
|
|
+
|
||
|
|
+ r = sd_pid_get_owner_uid(0, &uid);
|
||
|
|
if (r < 0)
|
||
|
|
- log_warning_errno(r, "Unable to parse $SYSTEMD_LESSSECURE, ignoring: %m");
|
||
|
|
+ log_debug_errno(r, "sd_pid_get_owner_uid() failed, enabling pager secure mode: %m");
|
||
|
|
+
|
||
|
|
+ use_secure_mode = r < 0 || uid != geteuid();
|
||
|
|
+
|
||
|
|
+ } else if (use_secure_mode < 0) {
|
||
|
|
+ log_warning_errno(use_secure_mode, "Unable to parse $SYSTEMD_PAGERSECURE, assuming true: %m");
|
||
|
|
+ use_secure_mode = true;
|
||
|
|
+ }
|
||
|
|
|
||
|
|
- if (setenv("LESSSECURE", "1", 1) < 0) {
|
||
|
|
- log_error_errno(errno, "Failed to set environment variable LESSSECURE: %m");
|
||
|
|
- _exit(EXIT_FAILURE);
|
||
|
|
- }
|
||
|
|
+ /* We generally always set variables used by less, even if we end up using a different pager.
|
||
|
|
+ * They shouldn't hurt in any case, and ideally other pagers would look at them too. */
|
||
|
|
+ if (use_secure_mode)
|
||
|
|
+ r = setenv("LESSSECURE", "1", 1);
|
||
|
|
+ else
|
||
|
|
+ r = unsetenv("LESSSECURE");
|
||
|
|
+ if (r < 0) {
|
||
|
|
+ log_error_errno(errno, "Failed to adjust environment variable LESSSECURE: %m");
|
||
|
|
+ _exit(EXIT_FAILURE);
|
||
|
|
}
|
||
|
|
|
||
|
|
- if (pager) {
|
||
|
|
+ if (trust_pager && pager) { /* The pager config might be set globally, and we cannot
|
||
|
|
+ * know if the user adjusted it to be appropriate for the
|
||
|
|
+ * secure mode. Thus, start the pager specified through
|
||
|
|
+ * envvars only when $SYSTEMD_PAGERSECURE was explicitly set
|
||
|
|
+ * as well. */
|
||
|
|
execlp(pager, pager, NULL);
|
||
|
|
execl("/bin/sh", "sh", "-c", pager, NULL);
|
||
|
|
}
|
||
|
|
|
||
|
|
- /* Debian's alternatives command for pagers is
|
||
|
|
- * called 'pager'. Note that we do not call
|
||
|
|
- * sensible-pagers here, since that is just a
|
||
|
|
- * shell script that implements a logic that
|
||
|
|
- * is similar to this one anyway, but is
|
||
|
|
- * Debian-specific. */
|
||
|
|
- execlp("pager", "pager", NULL);
|
||
|
|
+ /* Debian's alternatives command for pagers is called 'pager'. Note that we do not call
|
||
|
|
+ * sensible-pagers here, since that is just a shell script that implements a logic that is
|
||
|
|
+ * similar to this one anyway, but is Debian-specific. */
|
||
|
|
+ FOREACH_STRING(exe, "pager", "less", "more") {
|
||
|
|
+ /* Only less implements secure mode right now. */
|
||
|
|
+ if (use_secure_mode && !streq(exe, "less"))
|
||
|
|
+ continue;
|
||
|
|
|
||
|
|
- execlp("less", "less", NULL);
|
||
|
|
- execlp("more", "more", NULL);
|
||
|
|
+ execlp(exe, exe, NULL);
|
||
|
|
+ }
|
||
|
|
|
||
|
|
pager_fallback();
|
||
|
|
/* not reached */
|