wireguard: queueing: account for skb->protocol==0
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>
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@ -122,7 +122,7 @@ static netdev_tx_t wg_xmit(struct sk_buff *skb, struct net_device *dev)
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u32 mtu;
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int ret;
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if (unlikely(wg_skb_examine_untrusted_ip_hdr(skb) != skb->protocol)) {
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if (unlikely(!wg_check_packet_protocol(skb))) {
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ret = -EPROTONOSUPPORT;
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net_dbg_ratelimited("%s: Invalid IP packet\n", dev->name);
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goto err;
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@ -66,7 +66,7 @@ struct packet_cb {
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#define PACKET_PEER(skb) (PACKET_CB(skb)->keypair->entry.peer)
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/* Returns either the correct skb->protocol value, or 0 if invalid. */
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static inline __be16 wg_skb_examine_untrusted_ip_hdr(struct sk_buff *skb)
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static inline __be16 wg_examine_packet_protocol(struct sk_buff *skb)
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{
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if (skb_network_header(skb) >= skb->head &&
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(skb_network_header(skb) + sizeof(struct iphdr)) <=
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@ -81,6 +81,12 @@ static inline __be16 wg_skb_examine_untrusted_ip_hdr(struct sk_buff *skb)
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return 0;
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}
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static inline bool wg_check_packet_protocol(struct sk_buff *skb)
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{
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__be16 real_protocol = wg_examine_packet_protocol(skb);
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return real_protocol && skb->protocol == real_protocol;
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}
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static inline void wg_reset_packet(struct sk_buff *skb)
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{
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skb_scrub_packet(skb, true);
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@ -56,7 +56,7 @@ static int prepare_skb_header(struct sk_buff *skb, struct wg_device *wg)
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size_t data_offset, data_len, header_len;
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struct udphdr *udp;
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if (unlikely(wg_skb_examine_untrusted_ip_hdr(skb) != skb->protocol ||
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if (unlikely(!wg_check_packet_protocol(skb) ||
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skb_transport_header(skb) < skb->head ||
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(skb_transport_header(skb) + sizeof(struct udphdr)) >
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skb_tail_pointer(skb)))
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@ -388,7 +388,7 @@ static void wg_packet_consume_data_done(struct wg_peer *peer,
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*/
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skb->ip_summed = CHECKSUM_UNNECESSARY;
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skb->csum_level = ~0; /* All levels */
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skb->protocol = wg_skb_examine_untrusted_ip_hdr(skb);
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skb->protocol = wg_examine_packet_protocol(skb);
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if (skb->protocol == htons(ETH_P_IP)) {
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len = ntohs(ip_hdr(skb)->tot_len);
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if (unlikely(len < sizeof(struct iphdr)))
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