[PATCH v2] libxl__prepare_sockaddr_un

[Olaf Hering <olaf@xxxxxxxxx>]

libxl: remove usage of strncpy from libxl__prepare_sockaddr_un

The runtime check for the length of path already prevents malfunction.
But gcc does not detect this runtime check and reports incorrect
usage of strncpy. Remove the usage of strncpy and work directly with
the calculated path length.

In file included from /usr/include/string.h:495,
                 from libxl_internal.h:38,
                 from libxl_utils.c:20:
In function 'strncpy',
    inlined from 'libxl__prepare_sockaddr_un' at libxl_utils.c:1262:5:
/usr/include/bits/string_fortified.h:106:10: error: '__builtin_strncpy' 
specified bound 108 equals destination size [-Werror=stringop-truncation]
  106 |   return __builtin___strncpy_chk (__dest, __src, __len, __bos (__dest));
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors

Signed-off-by: Olaf Hering <olaf@xxxxxxxxx>
---
 tools/libxl/libxl_utils.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/tools/libxl/libxl_utils.c b/tools/libxl/libxl_utils.c
index f360f5e228..40885794c9 100644
--- a/tools/libxl/libxl_utils.c
+++ b/tools/libxl/libxl_utils.c
@@ -1252,14 +1252,16 @@ int libxl__prepare_sockaddr_un(libxl__gc *gc,
                                struct sockaddr_un *un, const char *path,
                                const char *what)
 {
-    if (sizeof(un->sun_path) <= strlen(path)) {
+    size_t len = strlen(path);
+
+    if (sizeof(un->sun_path) <= len) {
         LOG(ERROR, "UNIX socket path '%s' is too long for %s", path, what);
-        LOG(DEBUG, "Path must be less than %zu bytes", sizeof(un->sun_path));
+        LOG(DEBUG, "Path of len %zu must be less than %zu bytes", len, 
sizeof(un->sun_path));
         return ERROR_INVAL;
     }
     memset(un, 0, sizeof(struct sockaddr_un));
     un->sun_family = AF_UNIX;
-    strncpy(un->sun_path, path, sizeof(un->sun_path));
+    memcpy(un->sun_path, path, len);
     return 0;
 }