linux-kernel - [PATCH 4.9 11/78] packet: Dont write vnet header beyond end of buffer

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Date:   Mon, 18 Sep 2017 11:11:20 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Benjamin Poirier <bpoirier@...e.com>,
        Willem de Bruijn <willemb@...gle.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 4.9 11/78] packet: Dont write vnet header beyond end of buffer

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Benjamin Poirier <bpoirier@...e.com>


[ Upstream commit edbd58be15a957f6a760c4a514cd475217eb97fd ]

... which may happen with certain values of tp_reserve and maclen.

Fixes: 58d19b19cd99 ("packet: vnet_hdr support for tpacket_rcv")
Signed-off-by: Benjamin Poirier <bpoirier@...e.com>
Cc: Willem de Bruijn <willemb@...gle.com>
Acked-by: Willem de Bruijn <willemb@...gle.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/packet/af_packet.c |   12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -2151,6 +2151,7 @@ static int tpacket_rcv(struct sk_buff *s
 	struct timespec ts;
 	__u32 ts_status;
 	bool is_drop_n_account = false;
+	bool do_vnet = false;
 
 	/* struct tpacket{2,3}_hdr is aligned to a multiple of TPACKET_ALIGNMENT.
 	 * We may add members to them until current aligned size without forcing
@@ -2201,8 +2202,10 @@ static int tpacket_rcv(struct sk_buff *s
 		netoff = TPACKET_ALIGN(po->tp_hdrlen +
 				       (maclen < 16 ? 16 : maclen)) +
 				       po->tp_reserve;
-		if (po->has_vnet_hdr)
+		if (po->has_vnet_hdr) {
 			netoff += sizeof(struct virtio_net_hdr);
+			do_vnet = true;
+		}
 		macoff = netoff - maclen;
 	}
 	if (po->tp_version <= TPACKET_V2) {
@@ -2219,8 +2222,10 @@ static int tpacket_rcv(struct sk_buff *s
 					skb_set_owner_r(copy_skb, sk);
 			}
 			snaplen = po->rx_ring.frame_size - macoff;
-			if ((int)snaplen < 0)
+			if ((int)snaplen < 0) {
 				snaplen = 0;
+				do_vnet = false;
+			}
 		}
 	} else if (unlikely(macoff + snaplen >
 			    GET_PBDQC_FROM_RB(&po->rx_ring)->max_frame_len)) {
@@ -2233,6 +2238,7 @@ static int tpacket_rcv(struct sk_buff *s
 		if (unlikely((int)snaplen < 0)) {
 			snaplen = 0;
 			macoff = GET_PBDQC_FROM_RB(&po->rx_ring)->max_frame_len;
+			do_vnet = false;
 		}
 	}
 	spin_lock(&sk->sk_receive_queue.lock);
@@ -2258,7 +2264,7 @@ static int tpacket_rcv(struct sk_buff *s
 	}
 	spin_unlock(&sk->sk_receive_queue.lock);
 
-	if (po->has_vnet_hdr) {
+	if (do_vnet) {
 		if (__packet_rcv_vnet(skb, h.raw + macoff -
 					   sizeof(struct virtio_net_hdr))) {
 			spin_lock(&sk->sk_receive_queue.lock);