net-shapers: don't free reply skb after genlmsg_reply()

genlmsg_reply() hands the reply skb to netlink, and
netlink_unicast() consumes it on all return paths, whether the
skb is queued successfully or freed on an error path.

net_shaper_nl_get_doit() and net_shaper_nl_cap_get_doit()
currently jump to free_msg after genlmsg_reply() fails and call
nlmsg_free(msg), which can hit the same skb twice.

Return the genlmsg_reply() error directly and keep free_msg
only for pre-reply failures.

Fixes: 4b623f9 ("net-shapers: implement NL get operation")
Fixes: 553ea9f ("net: shaper: implement introspection support")
Cc: stable@vger.kernel.org
Signed-off-by: Paul Moses <p@1g4.org>
Link: https://patch.msgid.link/20260309173450.538026-2-p@1g4.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: jopamo

net/shaper/shaper.c

@@ -759,11 +759,7 @@ int net_shaper_nl_get_doit(struct sk_buff *skb, struct genl_info *info)
 	if (ret)
 		goto free_msg;
 
-	ret = genlmsg_reply(msg, info);
-	if (ret)
-		goto free_msg;
-
-	return 0;
+	return genlmsg_reply(msg, info);
 
 free_msg:
 	nlmsg_free(msg);
@@ -1313,10 +1309,7 @@ int net_shaper_nl_cap_get_doit(struct sk_buff *skb, struct genl_info *info)
 	if (ret)
 		goto free_msg;
 
-	ret =  genlmsg_reply(msg, info);
-	if (ret)
-		goto free_msg;
-	return 0;
+	return genlmsg_reply(msg, info);
 
 free_msg:
 	nlmsg_free(msg);