[PATCH net] pppoe: drop discovery frames with no MAC header

[Qingfang Deng]

Commit 8540827ebac6 ("pppoe: fix reception of frames with no mac
header") drops PPPoE session frames with no MAC header to avoid reading
uninitialized memory.

Apply the same to PPPoE discovery frames, as both functions read
eth_hdr(skb)->h_source.

Found by LLM static analysis, and reproduced using the same TUN
injection as described in the mentioned commit.

Fixes: 8540827ebac6 ("pppoe: fix reception of frames with no mac header")
Signed-off-by: Qingfang Deng <qingfang.deng@xxxxxxxxx>
---
 drivers/net/ppp/pppoe.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/net/ppp/pppoe.c b/drivers/net/ppp/pppoe.c
index ee0e318d6a2a..bdaa8cf8404b 100644
--- a/drivers/net/ppp/pppoe.c
+++ b/drivers/net/ppp/pppoe.c
@@ -460,6 +460,9 @@ static int pppoe_disc_rcv(struct sk_buff *skb, struct net_device *dev,
 	if (skb->pkt_type != PACKET_HOST)
 		goto abort;
 
+	if (skb_mac_header_len(skb) < ETH_HLEN)
+		goto abort;
+
 	if (!pskb_may_pull(skb, sizeof(struct pppoe_hdr)))
 		goto abort;
 
-- 
2.43.0