net/packet: fix overflow in tpacket_rcv

Using tp_reserve to calculate netoff can overflow as
tp_reserve is unsigned int and netoff is unsigned short.

This may lead to macoff receving a smaller value then
sizeof(struct virtio_net_hdr), and if po->has_vnet_hdr
is set, an out-of-bounds write will occur when
calling virtio_net_hdr_from_skb.

The bug is fixed by converting netoff to unsigned int
and checking if it exceeds USHRT_MAX.

This addresses CVE-2020-14386

Fixes: 8913336a7e8d ("packet: add PACKET_RESERVE sockopt")
Signed-off-by: Or Cohen <orcohen@paloaltonetworks.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index da8254e680f94da43ac2c817861e41b4865d40d5..2b33e977a905911c30ecc9d1a9920bccad04f23f 100644 (file)
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -2170,7 +2170,8 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
        int skb_len = skb->len;
        unsigned int snaplen, res;
        unsigned long status = TP_STATUS_USER;
-       unsigned short macoff, netoff, hdrlen;
+       unsigned short macoff, hdrlen;
+       unsigned int netoff;
        struct sk_buff *copy_skb = NULL;
        struct timespec64 ts;
        __u32 ts_status;
@@ -2239,6 +2240,10 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
                }
                macoff = netoff - maclen;
        }
+       if (netoff > USHRT_MAX) {
+               atomic_inc(&po->tp_drops);
+               goto drop_n_restore;
+       }
        if (po->tp_version <= TPACKET_V2) {
                if (macoff + snaplen > po->rx_ring.frame_size) {
                        if (po->copy_thresh &&