netdev - [PATCH net-next] net: netlink: catch attempts to send empty messages

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Message-ID: <20241218024400.824355-1-kuba@kernel.org>
Date: Tue, 17 Dec 2024 18:44:00 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: davem@...emloft.net
Cc: netdev@...r.kernel.org,
	edumazet@...gle.com,
	pabeni@...hat.com,
	Jakub Kicinski <kuba@...nel.org>
Subject: [PATCH net-next] net: netlink: catch attempts to send empty messages

syzbot can figure out a way to redirect a netlink message to a tap.
Sending empty skbs to devices is not valid and we end up hitting
a skb_assert_len() in __dev_queue_xmit().

Make catching these mistakes easier, assert the skb size directly
in netlink core.

Signed-off-by: Jakub Kicinski <kuba@...nel.org>
---
 net/netlink/af_netlink.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index f4e7b5e4bb59..85311226183a 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -1287,6 +1287,7 @@ static struct sk_buff *netlink_trim(struct sk_buff *skb, gfp_t allocation)
 {
 	int delta;
 
+	skb_assert_len(skb);
 	WARN_ON(skb->sk != NULL);
 	delta = skb->end - skb->tail;
 	if (is_vmalloc_addr(skb->head) || delta * 2 < skb->truesize)
-- 
2.47.1