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shared/pager: add support for more(1) pager in secure mode (#41503)

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The more(1) pager (part of util-linux) now supports secure mode,
which can be enabled with the MORESECURE environment variable.

Adding support for more(1) in secure mode serves as an alternative
for systems that do not have less installed or for users who prefer
it.

Commit d2fce960f9cac740 introduced secure mode in more(1) and the
new feature is available in version 2.42 of util-linux.
This commit is contained in:
Lennart Poettering
2026-05-06 14:30:29 +02:00
committed by GitHub
parent f6363a0b1d df87d75038
commit e0ea854328
3 changed files with 19 additions and 9 deletions
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README
+3 -3
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@@ -264,9 +264,9 @@ REQUIREMENTS:
During runtime, you need the following additional
dependencies:
util-linux >= v2.27.1 required (including but not limited to: mount,
umount, swapon, swapoff, sulogin,
agetty, fsck)
util-linux >= v2.42 required (including but not limited to: mount,
umount, swapon, swapoff, sulogin,
agetty, fsck, more)
dbus >= 1.4.0 (strictly speaking optional, but recommended)
NOTE: If using dbus < 1.9.18, you should override the default
policy directory (--with-dbuspolicydir=/etc/dbus-1/system.d).
man/common-variables.xml
+7 -4
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@@ -190,11 +190,14 @@
allowing untrusted users to execute commands with elevated privileges.</para>
<para>This option takes a boolean argument. When set to true, the "secure mode" of the pager is
enabled. In "secure mode", <option>LESSSECURE=1</option> will be set when invoking the pager, which
instructs the pager to disable commands that open or create new files or start new subprocesses.
enabled. In "secure mode", <option>LESSSECURE=1</option> and <option>PAGERSECURE=1</option> will be set
when invoking the pager, which instructs the pager to disable commands that open or create new files or
start new subprocesses.
Currently only <citerefentry
project='man-pages'><refentrytitle>less</refentrytitle><manvolnum>1</manvolnum></citerefentry> is known
to understand this variable and implement "secure mode".</para>
project='man-pages'><refentrytitle>less</refentrytitle><manvolnum>1</manvolnum></citerefentry> and
<citerefentry
project='man-pages'><refentrytitle>more</refentrytitle><manvolnum>1</manvolnum></citerefentry> are known
to understand these variables, respectively, and implement "secure mode".</para>
<para>When set to false, no limitation is placed on the pager. Setting
<varname>SYSTEMD_PAGERSECURE=0</varname> or not removing it from the inherited environment may allow
src/shared/pager.c
+9 -2
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@@ -206,6 +206,13 @@ void pager_open(PagerFlags flags) {
_exit(EXIT_FAILURE);
}
/* Some pager implementations support the PAGERSECURE environment variable, e.g. more(1) */
r = set_unset_env("PAGERSECURE", use_secure_mode ? "1" : NULL, true);
if (r < 0) {
log_error_errno(r, "Failed to adjust environment variable PAGERSECURE: %m");
_exit(EXIT_FAILURE);
}
if (trust_pager && pager_args) { /* 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
@@ -228,8 +235,8 @@ void pager_open(PagerFlags flags) {
static const char* pagers[] = { "pager", "less", "more", "(built-in)" };
for (unsigned i = 0; i < ELEMENTSOF(pagers); i++) {
/* Only less (and our trivial fallback) implement secure mode right now. */
if (use_secure_mode && !STR_IN_SET(pagers[i], "less", "(built-in)"))
/* Only less, more (and our trivial fallback) implement secure mode right now. */
if (use_secure_mode && !STR_IN_SET(pagers[i], "less", "more", "(built-in)"))
continue;
r = loop_write(exe_name_pipe[1], pagers[i], strlen(pagers[i]) + 1);