nspawn: Simplify tmpfs_patch_options() usage, and trickle that up

One of the things that tmpfs_patch_options does is take an (optional) UID,
and insert "uid=${UID},gid=${UID}" into the options string.  So we need a
uid_t argument, and a way of telling if we should use it.  Fortunately,
that is built in to the uid_t type by having UID_INVALID as a possible
value.

So this is really a feature that requires one argument.  Yet, it is somehow
taking 4!  That is absurd.  Simplify it to only take one argument, and have
that trickle all the way up to mount_all()'s usage.

Now, in may of the uses, the argument becomes

    uid_shift == 0 ? UID_INVALID : uid_shift

because it used to treat uid_shift=0 as invalid unless the patch_ids flag
was also set.  This keeps the behavior the same.  Note that in all cases
where it is invoked, if !use_userns (sometimes called !userns), then
uid_shift is 0; we don't have to add any checks for that.

That said, I'm pretty sure that "uid=0" and not setting "uid=" are the
same, but Christian Brauner seemed to not think so when implementing the
cgns support.  https://github.com/systemd/systemd/pull/3589

(cherry picked from commit 2fa017f16922776ff9751dc22031c7ee49920729)

3 files changed, 10 insertions, 19 deletions

diff --git a/src/nspawn/nspawn-mount.c b/src/nspawn/nspawn-mount.c
index 3613a179fe..21684aa49b 100644
--- a/src/nspawn/nspawn-mount.c
+++ b/src/nspawn/nspawn-mount.c
@@ -329,17 +329,13 @@ int overlay_mount_parse(CustomMount **l, size_t *n, const char *s, bool read_onl
 
 static int tmpfs_patch_options(
                 const char *options,
-                bool userns,
-                uid_t uid_shift, uid_t uid_range,
-                bool patch_ids,
+                uid_t uid_shift,
                 const char *selinux_apifs_context,
                 char **ret) {
 
         char *buf = NULL;
 
-        if ((userns && uid_shift != 0) || patch_ids) {
-                assert(uid_shift != UID_INVALID);
-
+        if (uid_shift != UID_INVALID) {
                 if (asprintf(&buf, "%s%suid=" UID_FMT ",gid=" UID_FMT,
                              strempty(options), options ? "," : "",
                              uid_shift, uid_shift) < 0)
@@ -497,7 +493,7 @@ static int mkdir_userns_p(const char *prefix, const char *path, mode_t mode, uid
 
 int mount_all(const char *dest,
               MountSettingsMask mount_settings,
-              uid_t uid_shift, uid_t uid_range,
+              uid_t uid_shift,
               const char *selinux_apifs_context) {
 
 #define PROC_INACCESSIBLE(path)                                         \
@@ -646,10 +642,7 @@ int mount_all(const char *dest,
 
                 o = mount_table[k].options;
                 if (streq_ptr(mount_table[k].type, "tmpfs")) {
-                        if (in_userns)
-                                r = tmpfs_patch_options(o, use_userns, 0, uid_range, true, selinux_apifs_context, &options);
-                        else
-                                r = tmpfs_patch_options(o, use_userns, uid_shift, uid_range, false, selinux_apifs_context, &options);
+                        r = tmpfs_patch_options(o, in_userns ? 0 : uid_shift, selinux_apifs_context, &options);
                         if (r < 0)
                                 return log_oom();
                         if (r > 0)
@@ -752,7 +745,7 @@ static int mount_tmpfs(
                         return log_error_errno(r, "Creating mount point for tmpfs %s failed: %m", where);
         }
 
-        r = tmpfs_patch_options(m->options, userns, uid_shift, uid_range, false, selinux_apifs_context, &buf);
+        r = tmpfs_patch_options(m->options, uid_shift == 0 ? UID_INVALID : uid_shift, selinux_apifs_context, &buf);
         if (r < 0)
                 return log_oom();
         options = r > 0 ? buf : m->options;
@@ -985,7 +978,7 @@ static int mount_legacy_cgns_supported(
                  * uid/gid as seen from e.g. /proc/1/mountinfo. So we simply
                  * pass uid 0 and not uid_shift to tmpfs_patch_options().
                  */
-                r = tmpfs_patch_options("mode=755", userns, 0, uid_range, true, selinux_apifs_context, &options);
+                r = tmpfs_patch_options("mode=755", 0, selinux_apifs_context, &options);
                 if (r < 0)
                         return log_oom();
 
@@ -1087,7 +1080,7 @@ static int mount_legacy_cgns_unsupported(
         if (r == 0) {
                 _cleanup_free_ char *options = NULL;
 
-                r = tmpfs_patch_options("mode=755", userns, uid_shift, uid_range, false, selinux_apifs_context, &options);
+                r = tmpfs_patch_options("mode=755", uid_shift == 0 ? UID_INVALID : uid_shift, selinux_apifs_context, &options);
                 if (r < 0)
                         return log_oom();
 
@@ -1298,7 +1291,7 @@ int setup_volatile_state(
                 return log_error_errno(errno, "Failed to create %s: %m", directory);
 
         options = "mode=755";
-        r = tmpfs_patch_options(options, userns, uid_shift, uid_range, false, selinux_apifs_context, &buf);
+        r = tmpfs_patch_options(options, uid_shift == 0 ? UID_INVALID : uid_shift, selinux_apifs_context, &buf);
         if (r < 0)
                 return log_oom();
         if (r > 0)
@@ -1331,7 +1324,7 @@ int setup_volatile(
                 return log_error_errno(errno, "Failed to create temporary directory: %m");
 
         options = "mode=755";
-        r = tmpfs_patch_options(options, userns, uid_shift, uid_range, false, selinux_apifs_context, &buf);
+        r = tmpfs_patch_options(options, uid_shift == 0 ? UID_INVALID : uid_shift, selinux_apifs_context, &buf);
         if (r < 0)
                 return log_oom();
         if (r > 0)
diff --git a/src/nspawn/nspawn-mount.h b/src/nspawn/nspawn-mount.h
index b823282cbd..e948d02c2c 100644
--- a/src/nspawn/nspawn-mount.h
+++ b/src/nspawn/nspawn-mount.h
@@ -43,7 +43,7 @@ int bind_mount_parse(CustomMount **l, size_t *n, const char *s, bool read_only);
 int tmpfs_mount_parse(CustomMount **l, size_t *n, const char *s);
 int overlay_mount_parse(CustomMount **l, size_t *n, const char *s, bool read_only);
 
-int mount_all(const char *dest, MountSettingsMask mount_settings, uid_t uid_shift, uid_t uid_range, const char *selinux_apifs_context);
+int mount_all(const char *dest, MountSettingsMask mount_settings, uid_t uid_shift, const char *selinux_apifs_context);
 int mount_sysfs(const char *dest, MountSettingsMask mount_settings);
 
 int mount_cgroups(const char *dest, CGroupUnified unified_requested, bool userns, uid_t uid_shift, uid_t uid_range, const char *selinux_apifs_context, bool use_cgns);
diff --git a/src/nspawn/nspawn.c b/src/nspawn/nspawn.c
index 56877bd932..4a2c64ed86 100644
--- a/src/nspawn/nspawn.c
+++ b/src/nspawn/nspawn.c
@@ -2558,7 +2558,6 @@ static int inner_child(
         r = mount_all(NULL,
                       arg_mount_settings | MOUNT_IN_USERNS,
                       arg_uid_shift,
-                      arg_uid_range,
                       arg_selinux_apifs_context);
         if (r < 0)
                 return r;
@@ -2990,7 +2989,6 @@ static int outer_child(
         r = mount_all(directory,
                       arg_mount_settings,
                       arg_uid_shift,
-                      arg_uid_range,
                       arg_selinux_apifs_context);
         if (r < 0)
                 return r;