redonkable/alistair23-linux
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wireguard: queueing: account for skb->protocol==0

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We carry out checks to the effect of:

  if (skb->protocol != wg_examine_packet_protocol(skb))
    goto err;

By having wg_skb_examine_untrusted_ip_hdr return 0 on failure, this
means that the check above still passes in the case where skb->protocol
is zero, which is possible to hit with AF_PACKET:

  struct sockaddr_pkt saddr = { .spkt_device = "wg0" };
  unsigned char buffer[5] = { 0 };
  sendto(socket(AF_PACKET, SOCK_PACKET, /* skb->protocol = */ 0),
         buffer, sizeof(buffer), 0, (const struct sockaddr *)&saddr, sizeof(saddr));

Additional checks mean that this isn't actually a problem in the code
base, but I could imagine it becoming a problem later if the function is
used more liberally.

I would prefer to fix this by having wg_examine_packet_protocol return a
32-bit ~0 value on failure, which will never match any value of
skb->protocol, which would simply change the generated code from a mov
to a movzx. However, sparse complains, and adding __force casts doesn't
seem like a good idea, so instead we just add a simple helper function
to check for the zero return value. Since wg_examine_packet_protocol
itself gets inlined, this winds up not adding an additional branch to
the generated code, since the 0 return value already happens in a
mergable branch.

Reported-by: Fabian Freyer <fabianfreyer@radicallyopensecurity.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Jason A. Donenfeld 2020-03-18 18:30:45 -06:00 committed by David S. Miller
parent 551599edbf
commit a5588604af
3 changed files with 10 additions and 4 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

2
drivers/net/wireguard/device.c
View file

@ -122,7 +122,7 @@ static netdev_tx_t wg_xmit(struct sk_buff *skb, struct net_device *dev)
u32 mtu;
int ret;
if (unlikely(wg_skb_examine_untrusted_ip_hdr(skb) != skb->protocol)) {
if (unlikely(!wg_check_packet_protocol(skb))) {
ret = -EPROTONOSUPPORT;
net_dbg_ratelimited("%s: Invalid IP packet\n", dev->name);
goto err;

8
drivers/net/wireguard/queueing.h
View file

@ -66,7 +66,7 @@ struct packet_cb {
#define PACKET_PEER(skb) (PACKET_CB(skb)->keypair->entry.peer)
/* Returns either the correct skb->protocol value, or 0 if invalid. */
static inline __be16 wg_skb_examine_untrusted_ip_hdr(struct sk_buff *skb)
static inline __be16 wg_examine_packet_protocol(struct sk_buff *skb)
{
if (skb_network_header(skb) >= skb->head &&
(skb_network_header(skb) + sizeof(struct iphdr)) <=
@ -81,6 +81,12 @@ static inline __be16 wg_skb_examine_untrusted_ip_hdr(struct sk_buff *skb)
return 0;
}
static inline bool wg_check_packet_protocol(struct sk_buff *skb)
{
__be16 real_protocol = wg_examine_packet_protocol(skb);
return real_protocol && skb->protocol == real_protocol;
}
static inline void wg_reset_packet(struct sk_buff *skb)
{
skb_scrub_packet(skb, true);

4
drivers/net/wireguard/receive.c
View file

@ -56,7 +56,7 @@ static int prepare_skb_header(struct sk_buff *skb, struct wg_device *wg)
size_t data_offset, data_len, header_len;
struct udphdr *udp;
if (unlikely(wg_skb_examine_untrusted_ip_hdr(skb) != skb->protocol ||
if (unlikely(!wg_check_packet_protocol(skb) ||
skb_transport_header(skb) < skb->head ||
(skb_transport_header(skb) + sizeof(struct udphdr)) >
skb_tail_pointer(skb)))
@ -388,7 +388,7 @@ static void wg_packet_consume_data_done(struct wg_peer *peer,
*/
skb->ip_summed = CHECKSUM_UNNECESSARY;
skb->csum_level = ~0; /* All levels */
skb->protocol = wg_skb_examine_untrusted_ip_hdr(skb);
skb->protocol = wg_examine_packet_protocol(skb);
if (skb->protocol == htons(ETH_P_IP)) {
len = ntohs(ip_hdr(skb)->tot_len);
if (unlikely(len < sizeof(struct iphdr)))