[systemd-devel] [PATCH 7/9] nspawn: escape paths in overlay mount options

[Richard Maw]

Overlayfs uses , as an option separator and : as a list separator. These
characters are both valid in file paths, so overlayfs allows file paths
which contain these characters to backslash escape these values.
---
 src/nspawn/nspawn.c | 63 +++++++++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 56 insertions(+), 7 deletions(-)

diff --git a/src/nspawn/nspawn.c b/src/nspawn/nspawn.c
index c40d50f..f7580f9 100644
--- a/src/nspawn/nspawn.c
+++ b/src/nspawn/nspawn.c
@@ -1237,6 +1237,42 @@ static int mount_tmpfs(const char *dest, CustomMount *m) {
         return 0;
 }
 
+static char *escaped_overlay_path(const char *path) {
+        _cleanup_free_ char *colon_escaped = NULL;
+        char *comma_escaped = NULL;
+
+        colon_escaped = strreplace(path, ":", "\\:");
+        if (!colon_escaped)
+                return NULL;
+
+        comma_escaped = strreplace(colon_escaped, ",", "\\,");
+
+        return comma_escaped;
+}
+
+static char *joined_and_escaped_lower_dirs(char * const *lower) {
+        _cleanup_free_ char *s = NULL;
+        char *ret = NULL;
+        char * const *path;
+        bool first = true;
+
+        STRV_FOREACH_BACKWARDS(path, lower) {
+                _cleanup_free_ char *escaped_path = NULL;
+                escaped_path = escaped_overlay_path(*path);
+                if (first) {
+                        if (!strextend(&s, escaped_path, NULL))
+                                return NULL;
+                        first = false;
+                } else
+                        if (!strextend(&s, ":", escaped_path, NULL))
+                                return NULL;
+        }
+
+        ret = s;
+        s = NULL;
+        return ret;
+}
+
 static int mount_overlay(const char *dest, CustomMount *m) {
         _cleanup_free_ char *lower = NULL;
         const char *where, *options;
@@ -1253,19 +1289,32 @@ static int mount_overlay(const char *dest, CustomMount *m) {
 
         (void) mkdir_p_label(m->source, 0755);
 
-        strv_reverse(m->lower);
-        lower = strv_join(m->lower, ":");
-        strv_reverse(m->lower);
+        lower = joined_and_escaped_lower_dirs(m->lower);
         if (!lower)
                 return log_oom();
 
-        if (m->read_only)
-                options = strjoina("lowerdir=", m->source, ":", lower);
-        else {
+        if (m->read_only) {
+                _cleanup_free_ char *escaped_source = NULL;
+
+                escaped_source = escaped_overlay_path(m->source);
+                if (!escaped_source)
+                        return log_oom();
+
+                options = strjoina("lowerdir=", escaped_source, ":", lower);
+        } else {
+                _cleanup_free_ char *escaped_source = NULL, *escaped_work_dir = NULL;
+
                 assert(m->work_dir);
                 (void) mkdir_label(m->work_dir, 0700);
 
-                options = strjoina("lowerdir=", lower, ",upperdir=", m->source, ",workdir=", m->work_dir);
+                escaped_source = escaped_overlay_path(m->source);
+                if (!escaped_source)
+                        return log_oom();
+                escaped_work_dir = escaped_overlay_path(m->work_dir);
+                if (!escaped_work_dir)
+                        return log_oom();
+
+                options = strjoina("lowerdir=", lower, ",upperdir=", escaped_source, ",workdir=", escaped_work_dir);
         }
 
         if (mount("overlay", where, "overlay", m->read_only ? MS_RDONLY : 0, options) < 0)
-- 
1.9.1