libbpf: Use proper errno value in nlattr

Return value of the validate_nla() function can be propagated all the
way up to users of libbpf API. In case of error this libbpf version
of validate_nla returns -1 which will be seen as -EPERM from user's
point of view. Instead, return a more reasonable -EINVAL.

Fixes: bbf48c18ee0c ("libbpf: add error reporting in XDP")
Suggested-by: Andrii Nakryiko <[e-mail]>
Signed-off-by: Anton Protopopov <[e-mail]>
Signed-off-by: Andrii Nakryiko <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

tools/lib/bpf/nlattr.c

···
 		minlen = nla_attr_minlen[pt->type];
 
 	if (libbpf_nla_len(nla) < minlen)
-		return -1;
+		return -EINVAL;
 
 	if (pt->maxlen && libbpf_nla_len(nla) > pt->maxlen)
-		return -1;
+		return -EINVAL;
 
 	if (pt->type == LIBBPF_NLA_STRING) {
 		char *data = libbpf_nla_data(nla);
 
 		if (data[libbpf_nla_len(nla) - 1] != '\0')
-			return -1;
+			return -EINVAL;
 	}
 
 	return 0;
···
 		if (policy) {
 			err = validate_nla(nla, maxtype, policy);
 			if (err < 0)
-				goto errout;
+				return err;
 		}
 
-		if (tb[type])
+		if (tb[type]) {
 			pr_warn("Attribute of type %#x found multiple times in message, "
 				"previous attribute is being ignored.\n", type);
+		}
 
 		tb[type] = nla;
 	}
 
-	err = 0;
-errout:
-	return err;
+	return 0;
 }
 
 /**