implement a union to pad out file_handle

Cases where name_to_handle_at is used allocated the full struct to be
MAX_HANDLE_SZ, and assigned this size to handle_bytes. This is wrong
since handle_bytes should describe the length of the flexible array
member and not the whole struct.

Define a union type which includes sufficient padding to allow
assignment of MAX_HANDLE_SZ to be correct.

1 files changed, 4 insertions, 7 deletions

diff --git a/src/tmpfiles/tmpfiles.c b/src/tmpfiles/tmpfiles.c
index 33e7cbc05d..04b472da97 100644
--- a/src/tmpfiles/tmpfiles.c
+++ b/src/tmpfiles/tmpfiles.c
@@ -217,19 +217,16 @@ static bool unix_socket_alive(const char *fn) {
 }
 
 static int dir_is_mount_point(DIR *d, const char *subdir) {
-        struct file_handle *h;
+        union file_handle_union h = { .handle.handle_bytes = MAX_HANDLE_SZ };
         int mount_id_parent, mount_id;
         int r_p, r;
 
-        h = alloca(MAX_HANDLE_SZ);
-
-        h->handle_bytes = MAX_HANDLE_SZ;
-        r_p = name_to_handle_at(dirfd(d), ".", h, &mount_id_parent, 0);
+        r_p = name_to_handle_at(dirfd(d), ".", &h.handle, &mount_id_parent, 0);
         if (r_p < 0)
                 r_p = -errno;
 
-        h->handle_bytes = MAX_HANDLE_SZ;
-        r = name_to_handle_at(dirfd(d), subdir, h, &mount_id, 0);
+        h.handle.handle_bytes = MAX_HANDLE_SZ;
+        r = name_to_handle_at(dirfd(d), subdir, &h.handle, &mount_id, 0);
         if (r < 0)
                 r = -errno;