attr: Warn application if nla_parse() observes same attribute multiple times

Use a debugging message to warn applications if an attribute is
found multiple times in the same message. It is perfectly valid
to rely on this behaviour but it is likely to indicate a bug.

Signed-off-by: Thomas Graf <tgraf@suug.ch>

1 files changed, 13 insertions, 8 deletions

diff --git a/lib/attr.c b/lib/attr.c
index 093ffb5..e6efe4e 100644
--- a/lib/attr.c
+++ b/lib/attr.c
@@ -254,15 +254,20 @@ int nla_parse(struct nlattr *tb[], int maxtype, struct nlattr *head, int len,
 		if (type == 0)
 			continue;
 
-		if (type <= maxtype) {
-			if (policy) {
-				err = validate_nla(nla, maxtype, policy);
-				if (err < 0)
-					goto errout;
-			}
-
-			tb[type] = nla;
+		if (type > maxtype)
+			continue;
+
+		if (policy) {
+			err = validate_nla(nla, maxtype, policy);
+			if (err < 0)
+				goto errout;
 		}
+
+		if (tb[type])
+			NL_DBG(1, "Attribute of type %#x found multiple times in message, "
+				  "previous attribute is being ignored.\n", type);
+
+		tb[type] = nla;
 	}
 
 	if (rem > 0)