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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: 8913336a7e ("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>
This commit is contained in:
Or Cohen 2020-09-03 21:05:28 -07:00 committed by Linus Torvalds
parent b25d1dc947
commit acf69c9462
1 changed files with 6 additions and 1 deletions
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7
net/packet/af_packet.c
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@ -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 &&