[PATCH net 2/2] tun: add missing verification for short frame

[Dongli Zhang]

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/1717026141-25716-1-git-send-email-si-wei.liu@xxxxxxxxxx/
Fixes: 043d222f93ab ("tuntap: accept an array of XDP buffs through sendmsg()")
Cc: Si-Wei Liu <si-wei.liu@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Dongli Zhang <dongli.zhang@xxxxxxxxxx>
Reviewed-by: Si-Wei Liu <si-wei.liu@xxxxxxxxxx>
Reviewed-by: Willem de Bruijn <willemb@xxxxxxxxxx>
Reviewed-by: Paolo Abeni <pabeni@xxxxxxxxxx>
Reviewed-by: Jason Wang <jasowang@xxxxxxxxxx>
---
 drivers/net/tun.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 9b24861464bc..1d06c560c5e6 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -2455,6 +2455,9 @@ 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) {
-- 
2.34.1