unshare: allow custom uid/gid mappings in userns

Two new options are added: `--map-user=<uid>` and `--map-group=<gid>`
for custom user and group mappings respectively. These are just
generalizations of the existing `--map-root-user` and
`--map-current-user` options.

As a side effect of this commit, specifying both `--map-root-user` and
`--map-current-user` no longer causes an error. Instead, the last
occurrence takes precedence.

Addresses: https://github.com/karelzak/util-linux/issues/885
Signed-off-by: Matthew Harm Bekkema <id@mbekkema.name>

diff --git a/sys-utils/unshare.1 b/sys-utils/unshare.1
index 957f7017182f82bbf627c1eb62a067c6e700953b..92a3f1c714e033c7f0fd5ae780e595973b52c67e 100644 (file)
--- a/sys-utils/unshare.1
+++ b/sys-utils/unshare.1
@@ -169,6 +169,16 @@ implies creating a new mount namespace since the /proc mount would otherwise
 mess up existing programs on the system.  The new proc filesystem is explicitly
 mounted as private (with MS_PRIVATE|MS_REC).
 .TP
+.BR \-\-map\-user=\fIuid
+Run the program only after the current effective user ID has been mapped to \fIuid\fP.
+If this option is specified multiple times, the last occurrence takes precedence.
+This option implies \fB\-\-user\fR.
+.TP
+.BR \-\-map\-group=\fIgid
+Run the program only after the current effective group ID has been mapped to \fIgid\fP.
+If this option is specified multiple times, the last occurrence takes precedence.
+This option implies \fB\-\-setgroups=deny\fR and \fB\-\-user\fR.
+.TP
 .BR \-r , " \-\-map\-root\-user"
 Run the program only after the current effective user and group IDs have been mapped to
 the superuser UID and GID in the newly created user namespace.  This makes it possible to
@@ -177,11 +187,13 @@ namespaces (such as configuring interfaces in the network namespace or mounting
 the mount namespace) even when run unprivileged.  As a mere convenience feature, it does not support
 more sophisticated use cases, such as mapping multiple ranges of UIDs and GIDs.
 This option implies \fB\-\-setgroups=deny\fR and \fB\-\-user\fR.
+This option is equivalent to \fB\-\-map-user=0 \-\-map-group=0\fR.
 .TP
 .BR \-c , " \-\-map\-current\-user"
 Run the program only after the current effective user and group IDs have been mapped to
 the same UID and GID in the newly created user namespace. This option implies
 \fB\-\-setgroups=deny\fR and \fB\-\-user\fR.
+This option is equivalent to \fB\-\-map-user=$(id -ru) \-\-map-group=$(id -rg)\fR.
 .TP
 .BR "\-\-propagation private" | shared | slave | unchanged
 Recursively set the mount propagation flag in the new mount namespace.  The default

diff --git a/sys-utils/unshare.c b/sys-utils/unshare.c
index 8652ebdaf8fa01cca9a74fa2156968c22a57c5fe..06c95c06ae2808cc53660c635f93da31b9d2f207 100644 (file)
--- a/sys-utils/unshare.c
+++ b/sys-utils/unshare.c
@@ -77,12 +77,6 @@ enum {
        SETGROUPS_ALLOW = 1,
 };
 
-enum {
-       MAP_USER_NONE,
-       MAP_USER_ROOT,
-       MAP_USER_CURRENT,
-};
-
 static const char *setgroups_strings[] =
 {
        [SETGROUPS_DENY] = "deny",
@@ -288,6 +282,8 @@ static void __attribute__((__noreturn__)) usage(void)
        fputs(_(" -T, --time[=<file>]       unshare time namespace\n"), out);
        fputs(USAGE_SEPARATOR, out);
        fputs(_(" -f, --fork                fork before launching <program>\n"), out);
+       fputs(_(" --map-user=<uid>          map current user to uid (implies --user)\n"), out);
+       fputs(_(" --map-group=<gid>         map current group to gid (implies --user)\n"), out);
        fputs(_(" -r, --map-root-user       map current user to root (implies --user)\n"), out);
        fputs(_(" -c, --map-current-user    map current user to itself (implies --user)\n"), out);
        fputs(USAGE_SEPARATOR, out);
@@ -323,6 +319,8 @@ int main(int argc, char *argv[])
                OPT_KEEPCAPS,
                OPT_MONOTONIC,
                OPT_BOOTTIME,
+               OPT_MAPUSER,
+               OPT_MAPGROUP,
        };
        static const struct option longopts[] = {
                { "help",          no_argument,       NULL, 'h'             },
@@ -340,6 +338,8 @@ int main(int argc, char *argv[])
                { "fork",          no_argument,       NULL, 'f'             },
                { "kill-child",    optional_argument, NULL, OPT_KILLCHILD   },
                { "mount-proc",    optional_argument, NULL, OPT_MOUNTPROC   },
+               { "map-user",      required_argument, NULL, OPT_MAPUSER     },
+               { "map-group",     required_argument, NULL, OPT_MAPGROUP    },
                { "map-root-user", no_argument,       NULL, 'r'             },
                { "map-current-user", no_argument,    NULL, 'c'             },
                { "propagation",   required_argument, NULL, OPT_PROPAGATION },
@@ -356,7 +356,9 @@ int main(int argc, char *argv[])
 
        int setgrpcmd = SETGROUPS_NONE;
        int unshare_flags = 0;
-       int c, forkit = 0, mapuser = MAP_USER_NONE;
+       int c, forkit = 0;
+       uid_t mapuser = -1;
+       gid_t mapgroup = -1;
        int kill_child_signo = 0; /* 0 means --kill-child was not used */
        const char *procmnt = NULL;
        const char *newroot = NULL;
@@ -428,21 +430,23 @@ int main(int argc, char *argv[])
                        unshare_flags |= CLONE_NEWNS;
                        procmnt = optarg ? optarg : "/proc";
                        break;
+               case OPT_MAPUSER:
+                       unshare_flags |= CLONE_NEWUSER;
+                       mapuser = strtoul_or_err(optarg, _("failed to parse uid"));
+                       break;
+               case OPT_MAPGROUP:
+                       unshare_flags |= CLONE_NEWUSER;
+                       mapgroup = strtoul_or_err(optarg, _("failed to parse gid"));
+                       break;
                case 'r':
-                       if (mapuser == MAP_USER_CURRENT)
-                               errx(EXIT_FAILURE, _("options --map-root-user and "
-                                       "--map-current-user are mutually exclusive"));
-
                        unshare_flags |= CLONE_NEWUSER;
-                       mapuser = MAP_USER_ROOT;
+                       mapuser = 0;
+                       mapgroup = 0;
                        break;
                case 'c':
-                       if (mapuser == MAP_USER_ROOT)
-                               errx(EXIT_FAILURE, _("options --map-root-user and "
-                                       "--map-current-user are mutually exclusive"));
-
                        unshare_flags |= CLONE_NEWUSER;
-                       mapuser = MAP_USER_CURRENT;
+                       mapuser = real_euid;
+                       mapgroup = real_egid;
                        break;
                case OPT_SETGROUPS:
                        setgrpcmd = setgroups_str2id(optarg);
@@ -561,33 +565,23 @@ int main(int argc, char *argv[])
        if (kill_child_signo != 0 && prctl(PR_SET_PDEATHSIG, kill_child_signo) < 0)
                err(EXIT_FAILURE, "prctl failed");
 
+        if (mapuser != (uid_t) -1)
+               map_id(_PATH_PROC_UIDMAP, mapuser, real_euid);
+
         /* Since Linux 3.19 unprivileged writing of /proc/self/gid_map
          * has been disabled unless /proc/self/setgroups is written
          * first to permanently disable the ability to call setgroups
          * in that user namespace. */
-        switch (mapuser) {
-        case MAP_USER_ROOT:
+       if (mapgroup != (gid_t) -1) {
                if (setgrpcmd == SETGROUPS_ALLOW)
                        errx(EXIT_FAILURE, _("options --setgroups=allow and "
-                                       "--map-root-user are mutually exclusive"));
-
+                                       "--map-group are mutually exclusive"));
                setgroups_control(SETGROUPS_DENY);
-               map_id(_PATH_PROC_UIDMAP, 0, real_euid);
-               map_id(_PATH_PROC_GIDMAP, 0, real_egid);
-                break;
-        case MAP_USER_CURRENT:
-               if (setgrpcmd == SETGROUPS_ALLOW)
-                       errx(EXIT_FAILURE, _("options --setgroups=allow and "
-                                       "--map-current-user are mutually exclusive"));
+               map_id(_PATH_PROC_GIDMAP, mapgroup, real_egid);
+       }
 
-               setgroups_control(SETGROUPS_DENY);
-               map_id(_PATH_PROC_UIDMAP, real_euid, real_euid);
-               map_id(_PATH_PROC_GIDMAP, real_egid, real_egid);
-                break;
-        case MAP_USER_NONE:
-               if (setgrpcmd != SETGROUPS_NONE)
-                       setgroups_control(setgrpcmd);
-        }
+       if (setgrpcmd != SETGROUPS_NONE)
+               setgroups_control(setgrpcmd);
 
        if ((unshare_flags & CLONE_NEWNS) && propagation)
                set_propagation(propagation);