genl: reject invalid group names in genl_family_add_grp()

The compiler warns about string truncation:

  In function ‘genl_family_add_grp’,
      inlined from ‘family_clone’ at lib/genl/family.c:81:9,
      inlined from ‘family_clone’ at lib/genl/family.c:66:12:
  lib/genl/family.c:376:2: error: ‘strncpy’ output may be truncated copying 15 bytes from a string of length 15 [-Werror=stringop-truncation]
    376 |  strncpy(grp->name, name, GENL_NAMSIZ - 1);
        |  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Obvioulsy, it's a bug to use an invalid group name. But better
handle it by checking for a suitable string length.

Also use _nl_strncpy() which asserts that no truncation occurs.

1 files changed, 9 insertions, 3 deletions

diff --git a/lib/genl/family.c b/lib/genl/family.c
index c98e5e1..eeb1fef 100644
--- a/lib/genl/family.c
+++ b/lib/genl/family.c
@@ -24,6 +24,8 @@
 #include <netlink/genl/family.h>
 #include <netlink/utils.h>
 
+#include "netlink-private/utils.h"
+
 /** @cond SKIP */
 #define FAMILY_ATTR_ID		0x01
 #define FAMILY_ATTR_NAME	0x02
@@ -364,16 +366,20 @@ int genl_family_add_op(struct genl_family *family, int id, int flags)
 }
 
 int genl_family_add_grp(struct genl_family *family, uint32_t id,
-	       		const char *name)
+                        const char *name)
 {
-	struct genl_family_grp *grp;  
+	struct genl_family_grp *grp;
+
+	if (   !name
+	    || strlen (name) >= GENL_NAMSIZ)
+		return -NLE_INVAL;
 
 	grp = calloc(1, sizeof(*grp));
 	if (grp == NULL)
 		return -NLE_NOMEM;
 
 	grp->id = id;
-	strncpy(grp->name, name, GENL_NAMSIZ - 1);
+	_nl_strncpy(grp->name, name, GENL_NAMSIZ);
 
 	nl_list_add_tail(&grp->list, &family->gf_mc_grps);