chase-symlinks: avoid using stack allocation for potentially huge paths

let's better be safe and use heap allocation for paths which might be
unbounded.

In particular as previously we copied the stack memory to heap anyway,
via a noop path_make_absolute_cwd() call.

diff --git a/src/basic/chase-symlinks.c b/src/basic/chase-symlinks.c
index 8558944a69ce96057abf2ef3e09b056c01855120..3e2f2a66221aebefc71da38bcf8de99f549f75c4 100644 (file)
--- a/src/basic/chase-symlinks.c
+++ b/src/basic/chase-symlinks.c
@@ -84,6 +84,10 @@ int chase_symlinks(
         if (isempty(path))
                 return -EINVAL;
 
+        /* We don't support relative paths in combination with a root directory */
+        if (FLAGS_SET(flags, CHASE_PREFIX_ROOT) && !path_is_absolute(path))
+                return -EINVAL;
+
         /* This is a lot like canonicalize_file_name(), but takes an additional "root" parameter, that allows following
          * symlinks relative to a root directory, instead of the root of the host.
          *
@@ -161,17 +165,17 @@ int chase_symlinks(
                 path_simplify(root);
 
                 if (flags & CHASE_PREFIX_ROOT) {
-                        /* We don't support relative paths in combination with a root directory */
-                        if (!path_is_absolute(path))
-                                return -EINVAL;
-
-                        path = prefix_roota(root, path);
+                        buffer = path_join(root, path);
+                        if (!buffer)
+                                return -ENOMEM;
                 }
         }
 
-        r = path_make_absolute_cwd(path, &buffer);
-        if (r < 0)
-                return r;
+        if (!buffer) {
+                r = path_make_absolute_cwd(path, &buffer);
+                if (r < 0)
+                        return r;
+        }
 
         fd = open(root ?: "/", O_CLOEXEC|O_DIRECTORY|O_PATH);
         if (fd < 0)