Revert "Mount all fs nosuid when NoNewPrivileges=yes"

This reverts commit d8e3c31bd8e307c8defc759424298175aa0f7001.

A poorly documented fact is that SELinux unfortunately uses nosuid mount flag
to specify that also a fundamental feature of SELinux, domain transitions, must
not be allowed either. While this could be mitigated case by case by changing
the SELinux policy to use `nosuid_transition`, such mitigations would probably
have to be added everywhere if systemd used automatic nosuid mount flags when
`NoNewPrivileges=yes` would be implied. This isn't very desirable from SELinux
policy point of view since also untrusted mounts in service's mount namespaces
could start triggering domain transitions.

Alternatively there could be directives to override this behavior globally or
for each service (for example, new directives `SUIDPaths=`/`NoSUIDPaths=` or
more generic mount flag applicators), but since there's little value of the
commit by itself (setting NNP already disables most setuid functionality), it's
simpler to revert the commit. Such new directives could be used to implement
the original goal.

diff --git a/man/systemd.exec.xml b/man/systemd.exec.xml
index 96d18dd93bd85e096522d1b6e38c1d737153c1bf..893b56d93ad1968070159578378f6a87006ea1fb 100644 (file)
--- a/man/systemd.exec.xml
+++ b/man/systemd.exec.xml
@@ -675,10 +675,9 @@ CapabilityBoundingSet=~CAP_B CAP_C</programlisting>
         <varname>SystemCallArchitectures=</varname>,
         <varname>SystemCallFilter=</varname>, or
         <varname>SystemCallLog=</varname> are specified. Note that even if this setting is overridden
-        by them, <command>systemctl show</command> shows the original value of this setting. In case the
-        service will be run in a new mount namespace anyway, all file systems are mounted with MS_NOSUID
-        flag. Also see <ulink url="https://www.kernel.org/doc/html/latest/userspace-api/no_new_privs.html">
-        No New Privileges Flag</ulink>.</para></listitem>
+        by them, <command>systemctl show</command> shows the original value of this setting. Also see
+        <ulink url="https://www.kernel.org/doc/html/latest/userspace-api/no_new_privs.html">No New
+        Privileges Flag</ulink>.</para></listitem>
       </varlistentry>
 
       <varlistentry>

diff --git a/src/core/execute.c b/src/core/execute.c
index 5c958b327b9c9a924af96435bb12ad1d91678014..5bb41db888201defce6a0bbc10f35844af7e4ee9 100644 (file)
--- a/src/core/execute.c
+++ b/src/core/execute.c
@@ -3189,8 +3189,6 @@ static int apply_mount_namespace(
                         .protect_proc = context->protect_proc,
                         .proc_subset = context->proc_subset,
                         .private_ipc = context->private_ipc || context->ipc_namespace_path,
-                        /* If NNP is on, we can turn on MS_NOSUID, since it won't have any effect anymore. */
-                        .mount_nosuid = context->no_new_privileges,
                 };
         } else if (!context->dynamic_user && root_dir)
                 /*

diff --git a/src/core/namespace.c b/src/core/namespace.c
index 71fc73b9d30b81d40540e7725968298d16bff0f3..6d77ce9967424c57e1fd313bcdce26a6d748f737 100644 (file)
--- a/src/core/namespace.c
+++ b/src/core/namespace.c
@@ -1464,27 +1464,6 @@ static int make_noexec(const MountEntry *m, char **deny_list, FILE *proc_self_mo
         return 0;
 }
 
-static int make_nosuid(const MountEntry *m, FILE *proc_self_mountinfo) {
-        bool submounts = false;
-        int r = 0;
-
-        assert(m);
-        assert(proc_self_mountinfo);
-
-        submounts = !IN_SET(m->mode, EMPTY_DIR, TMPFS);
-
-        if (submounts)
-                r = bind_remount_recursive_with_mountinfo(mount_entry_path(m), MS_NOSUID, MS_NOSUID, NULL, proc_self_mountinfo);
-        else
-                r = bind_remount_one_with_mountinfo(mount_entry_path(m), MS_NOSUID, MS_NOSUID, proc_self_mountinfo);
-        if (r == -ENOENT && m->ignore)
-                return 0;
-        if (r < 0)
-                return log_debug_errno(r, "Failed to re-mount '%s'%s: %m", mount_entry_path(m),
-                                       submounts ? " and its submounts" : "");
-        return 0;
-}
-
 static bool namespace_info_mount_apivfs(const NamespaceInfo *ns_info) {
         assert(ns_info);
 
@@ -1681,17 +1660,6 @@ static int apply_mounts(
                 }
         }
 
-        /* Fourth round, flip the nosuid bits without a deny list. */
-        if (ns_info->mount_nosuid)
-                for (MountEntry *m = mounts; m < mounts + *n_mounts; ++m) {
-                        r = make_nosuid(m, proc_self_mountinfo);
-                        if (r < 0) {
-                                if (error_path && mount_entry_path(m))
-                                        *error_path = strdup(mount_entry_path(m));
-                                return r;
-                        }
-                }
-
         return 1;
 }
 

diff --git a/src/core/namespace.h b/src/core/namespace.h
index c9373a4adb1057ae63692d33242a1664f4e5a33f..737d6eae8b1e5d25d66fdc4d9e280bb971b4d94f 100644 (file)
--- a/src/core/namespace.h
+++ b/src/core/namespace.h
@@ -74,7 +74,6 @@ struct NamespaceInfo {
         bool mount_apivfs;
         bool protect_hostname;
         bool private_ipc;
-        bool mount_nosuid;
         ProtectHome protect_home;
         ProtectSystem protect_system;
         ProtectProc protect_proc;