Make systemctl --root look for files in the proper places

Running systemctl enable/disable/set-default/... with the --root
option under strace reveals that it accessed various files and
directories in the main fs, and not underneath the specified root.
This can lead to correct results only when the layout and
configuration in the container are identical, which often is not the
case. Fix this by adding the specified root to all file access
operations.

This patch does not handle some corner cases: symlinks which point
outside of the specified root might be interpreted differently than
they would be by the kernel if the specified root was the real root.
But systemctl does not create such symlinks by itself, and I think
this is enough of a corner case not to be worth the additional
complexity of reimplementing link chasing in systemd.

Also, simplify the code in a few places and remove an hypothetical
memory leak on error.

4 files changed, 68 insertions, 31 deletions

diff --git a/src/shared/install.c b/src/shared/install.c
index 2822e61880..487d0f660d 100644
--- a/src/shared/install.c
+++ b/src/shared/install.c
@@ -47,7 +47,9 @@ typedef struct {
 
 #define _cleanup_install_context_done_ _cleanup_(install_context_done)
 
-static int lookup_paths_init_from_scope(LookupPaths *paths, UnitFileScope scope) {
+static int lookup_paths_init_from_scope(LookupPaths *paths,
+                                        UnitFileScope scope,
+                                        const char *root_dir) {
         assert(paths);
         assert(scope >= 0);
         assert(scope < _UNIT_FILE_SCOPE_MAX);
@@ -57,6 +59,7 @@ static int lookup_paths_init_from_scope(LookupPaths *paths, UnitFileScope scope)
         return lookup_paths_init(paths,
                                  scope == UNIT_FILE_SYSTEM ? SYSTEMD_SYSTEM : SYSTEMD_USER,
                                  scope == UNIT_FILE_USER,
+                                 root_dir,
                                  NULL, NULL, NULL);
 }
 
@@ -701,7 +704,7 @@ int unit_file_link(
         assert(scope >= 0);
         assert(scope < _UNIT_FILE_SCOPE_MAX);
 
-        r = lookup_paths_init_from_scope(&paths, scope);
+        r = lookup_paths_init_from_scope(&paths, scope, root_dir);
         if (r < 0)
                 return r;
 
@@ -1473,7 +1476,7 @@ int unit_file_enable(
         assert(scope >= 0);
         assert(scope < _UNIT_FILE_SCOPE_MAX);
 
-        r = lookup_paths_init_from_scope(&paths, scope);
+        r = lookup_paths_init_from_scope(&paths, scope, root_dir);
         if (r < 0)
                 return r;
 
@@ -1513,7 +1516,7 @@ int unit_file_disable(
         assert(scope >= 0);
         assert(scope < _UNIT_FILE_SCOPE_MAX);
 
-        r = lookup_paths_init_from_scope(&paths, scope);
+        r = lookup_paths_init_from_scope(&paths, scope, root_dir);
         if (r < 0)
                 return r;
 
@@ -1577,7 +1580,7 @@ int unit_file_set_default(
         if (unit_name_to_type(file) != UNIT_TARGET)
                 return -EINVAL;
 
-        r = lookup_paths_init_from_scope(&paths, scope);
+        r = lookup_paths_init_from_scope(&paths, scope, root_dir);
         if (r < 0)
                 return r;
 
@@ -1617,7 +1620,7 @@ int unit_file_get_default(
         assert(scope < _UNIT_FILE_SCOPE_MAX);
         assert(name);
 
-        r = lookup_paths_init_from_scope(&paths, scope);
+        r = lookup_paths_init_from_scope(&paths, scope, root_dir);
         if (r < 0)
                 return r;
 
@@ -1675,12 +1678,13 @@ UnitFileState unit_file_get_state(
         if (!unit_name_is_valid(name, TEMPLATE_VALID))
                 return -EINVAL;
 
-        r = lookup_paths_init_from_scope(&paths, scope);
+        r = lookup_paths_init_from_scope(&paths, scope, root_dir);
         if (r < 0)
                 return r;
 
         STRV_FOREACH(i, paths.unit_path) {
                 struct stat st;
+                char *partial;
 
                 free(path);
                 path = NULL;
@@ -1689,10 +1693,14 @@ UnitFileState unit_file_get_state(
                         asprintf(&path, "%s/%s/%s", root_dir, *i, name);
                 else
                         asprintf(&path, "%s/%s", *i, name);
-
                 if (!path)
                         return -ENOMEM;
 
+                if (root_dir)
+                        partial = path + strlen(root_dir) + 1;
+                else
+                        partial = path;
+
                 /*
                  * Search for a unit file in our default paths, to
                  * be sure, that there are no broken symlinks.
@@ -1724,7 +1732,7 @@ UnitFileState unit_file_get_state(
                 else if (r > 0)
                         return state;
 
-                r = unit_file_can_install(&paths, root_dir, path, true);
+                r = unit_file_can_install(&paths, root_dir, partial, true);
                 if (r < 0 && errno != ENOENT)
                         return r;
                 else if (r > 0)
@@ -1832,7 +1840,7 @@ int unit_file_preset(
         assert(scope >= 0);
         assert(scope < _UNIT_FILE_SCOPE_MAX);
 
-        r = lookup_paths_init_from_scope(&paths, scope);
+        r = lookup_paths_init_from_scope(&paths, scope, root_dir);
         if (r < 0)
                 return r;
 
@@ -1902,7 +1910,7 @@ int unit_file_get_list(
         if (root_dir && scope != UNIT_FILE_SYSTEM)
                 return -EINVAL;
 
-        r = lookup_paths_init_from_scope(&paths, scope);
+        r = lookup_paths_init_from_scope(&paths, scope, root_dir);
         if (r < 0)
                 return r;
 
diff --git a/src/shared/path-lookup.c b/src/shared/path-lookup.c
index 63af43cdbb..c6b4ba1e22 100644
--- a/src/shared/path-lookup.c
+++ b/src/shared/path-lookup.c
@@ -198,6 +198,7 @@ int lookup_paths_init(
                 LookupPaths *p,
                 SystemdRunningAs running_as,
                 bool personal,
+                const char *root_dir,
                 const char *generator,
                 const char *generator_early,
                 const char *generator_late) {
@@ -275,11 +276,9 @@ int lookup_paths_init(
                 }
         }
 
-        if (!path_strv_canonicalize_absolute(p->unit_path, NULL))
+        if (!path_strv_canonicalize_absolute_uniq(p->unit_path, root_dir))
                 return -ENOMEM;
 
-        strv_uniq(p->unit_path);
-
         if (!strv_isempty(p->unit_path)) {
                 _cleanup_free_ char *t = strv_join(p->unit_path, "\n\t");
                 if (!t)
@@ -331,15 +330,12 @@ int lookup_paths_init(
                                 return -ENOMEM;
                 }
 
-                if (!path_strv_canonicalize_absolute(p->sysvinit_path, NULL))
+                if (!path_strv_canonicalize_absolute_uniq(p->sysvinit_path, root_dir))
                         return -ENOMEM;
 
-                if (!path_strv_canonicalize_absolute(p->sysvrcnd_path, NULL))
+                if (!path_strv_canonicalize_absolute_uniq(p->sysvrcnd_path, root_dir))
                         return -ENOMEM;
 
-                strv_uniq(p->sysvinit_path);
-                strv_uniq(p->sysvrcnd_path);
-
                 if (!strv_isempty(p->sysvinit_path)) {
                         _cleanup_free_ char *t = strv_join(p->sysvinit_path, "\n\t");
                         if (!t)
diff --git a/src/shared/path-lookup.h b/src/shared/path-lookup.h
index a3ef824a86..847a52f20a 100644
--- a/src/shared/path-lookup.h
+++ b/src/shared/path-lookup.h
@@ -43,5 +43,11 @@ SystemdRunningAs systemd_running_as_from_string(const char *s) _pure_;
 
 int user_config_home(char **config_home);
 
-int lookup_paths_init(LookupPaths *p, SystemdRunningAs running_as, bool personal, const char *generator, const char *generator_early, const char *generator_late);
+int lookup_paths_init(LookupPaths *p,
+                      SystemdRunningAs running_as,
+                      bool personal,
+                      const char *root_dir,
+                      const char *generator,
+                      const char *generator_early,
+                      const char *generator_late);
 void lookup_paths_free(LookupPaths *p);
diff --git a/src/shared/path-util.c b/src/shared/path-util.c
index 69fcb1660a..8bf9a3cf96 100644
--- a/src/shared/path-util.c
+++ b/src/shared/path-util.c
@@ -167,36 +167,63 @@ char **path_strv_canonicalize_absolute(char **l, const char *prefix) {
 
         STRV_FOREACH(s, l) {
                 char *t, *u;
+                _cleanup_free_ char *orig = NULL;
 
-                if (!path_is_absolute(*s))
+                if (!path_is_absolute(*s)) {
+                        free(*s);
                         continue;
+                }
 
                 if (prefix) {
-                        t = strappend(prefix, *s);
-                        free(*s);
-                        *s = NULL;
-
+                        orig = *s;
+                        t = strappend(prefix, orig);
                         if (!t) {
                                 enomem = true;
                                 continue;
                         }
-                } else {
+                } else
                         t = *s;
-                        *s = NULL;
-                }
 
                 errno = 0;
                 u = canonicalize_file_name(t);
                 if (!u) {
-                        if (errno == ENOENT)
-                                u = t;
-                        else {
+                        if (errno == ENOENT) {
+                                if (prefix) {
+                                        u = orig;
+                                        orig = NULL;
+                                        free(t);
+                                } else
+                                        u = t;
+                        } else {
                                 free(t);
                                 if (errno == ENOMEM || errno == 0)
                                         enomem = true;
 
                                 continue;
                         }
+                } else if (prefix) {
+                        char *x;
+
+                        free(t);
+                        x = path_startswith(u, prefix);
+                        if (x) {
+                                /* restore the slash if it was lost */
+                                if (!startswith(x, "/"))
+                                        *(--x) = '/';
+
+                                t = strdup(x);
+                                free(u);
+                                if (!t) {
+                                        enomem = true;
+                                        continue;
+                                }
+                                u = t;
+                        } else {
+                                /* canonicalized path goes outside of
+                                 * prefix, keep the original path instead */
+                                u = orig;
+                                orig = NULL;
+                        }
                 } else
                         free(t);