tun: add missing verification for short frame

jira VULN-8274
cve CVE-2024-41091
commit-author Dongli Zhang <[email protected]>
commit 0495848

The cited commit missed to check against the validity of the frame length
in the tun_xdp_one() path, which could cause a corrupted skb to be sent
downstack. Even before the skb is transmitted, the
tun_xdp_one-->eth_type_trans() may access the Ethernet header although it
can be less than ETH_HLEN. Once transmitted, this could either cause
out-of-bound access beyond the actual length, or confuse the underlayer
with incorrect or inconsistent header length in the skb metadata.

In the alternative path, tun_get_user() already prohibits short frame which
has the length less than Ethernet header size from being transmitted for
IFF_TAP.

This is to drop any frame shorter than the Ethernet header size just like
how tun_get_user() does.

CVE: CVE-2024-41091
Inspired-by: https://lore.kernel.org/netdev/[email protected]/
Fixes: 043d222 ("tuntap: accept an array of XDP buffs through sendmsg()")
	Cc: [email protected]
	Signed-off-by: Dongli Zhang <[email protected]>
	Reviewed-by: Si-Wei Liu <[email protected]>
	Reviewed-by: Willem de Bruijn <[email protected]>
	Reviewed-by: Paolo Abeni <[email protected]>
	Reviewed-by: Jason Wang <[email protected]>
Link: https://patch.msgid.link/[email protected]
	Signed-off-by: Jakub Kicinski <[email protected]>
(cherry picked from commit 0495848)
	Signed-off-by: Jeremy Allison <[email protected]>

Author: jallisonciq

drivers/net/tun.c

@@ -2415,6 +2415,9 @@ static int tun_xdp_one(struct tun_struct *tun,
 	bool skb_xdp = false;
 	struct page *page;
 
+	if (unlikely(datasize < ETH_HLEN))
+		return -EINVAL;
+
 	xdp_prog = rcu_dereference(tun->xdp_prog);
 	if (xdp_prog) {
 		if (gso->gso_type) {