virtio_net_hdr_tnl_to_skb() trusts the virtio header to describe a
UDP tunnel over IPv4 or IPv6, but never checks that the frame actually
carries such outer headers. Because VIRTIO_NET_HDR_F_NEEDS_CSUM is
mandatory for tunnel GSO, __virtio_net_hdr_to_skb() skips the flow
dissector, so virtio_net_hdr_match_proto() is never applied either.
A guest (or a tap writer) can then inject a frame with an arbitrary
outer ethertype, for example ETH_P_NSH, with SKB_GSO_UDP_TUNNEL set.
The GSO stack then runs nsh_gso_segment() on top of the UDP tunnel
segmentation, which assumes a different header layout. The result is
segments with skb->data before skb->head, and a host crash in
skb_under_panic() as soon as a later layer pushes a header:
skbuff: skb_under_panic: ... put:4 ... dev:gretap1
kernel BUG at net/core/skbuff.c:215!
skb_push
__gre_xmit
gre_tap_xmit
...
tun_get_user
Validate the outer headers with the parsing helpers from Michael's
series "net: resolve uncommon partial checksums at ingress":
- locate the L3 header from the device type: Ethernet with optional
VLAN tags, or the network header set by the caller. skb->protocol is
not trusted when it disagrees with the frame.
- require the outer L3 protocol to match the declared tunnel type.
- require the outer UDP header exactly at outer_th_offset, after IPv4
options or IPv6 extension headers, and reject fragments.
Unlike the original helpers, ipv6_find_hdr() stops at an AH header,
as Willem suggested in the review of that series.
Fixes: a2fb4bc4e2a6 ("net: implement virtio helpers to handle UDP GSO
tunneling.")
Reported-by: Hassan Sultan <[email protected]>
Suggested-by: Willem de Bruijn <[email protected]>
Link:
https://lore.kernel.org/netdev/93d0e37c99711bebdf60c120af03010455c2f2e2.1793276116.git....@redhat.com/
Cc: Willem de Bruijn <[email protected]>
Cc: Michael S. Tsirkin <[email protected]>
Co-developed-by: Michael S. Tsirkin <[email protected]>
Signed-off-by: Michael S. Tsirkin <[email protected]>
Signed-off-by: Eric Dumazet <[email protected]>
---
include/linux/virtio_net.h | 169 +++++++++++++++++++++++++++++++++++++
1 file changed, 169 insertions(+)
diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h
index d6466f96cdd0..b9c8babb1fd7 100644
--- a/include/linux/virtio_net.h
+++ b/include/linux/virtio_net.h
@@ -5,7 +5,10 @@
#include <linux/if_vlan.h>
#include <linux/ip.h>
#include <linux/ipv6.h>
+#include <linux/netdevice.h>
#include <linux/udp.h>
+#include <net/ip.h>
+#include <net/ipv6.h>
#include <net/tcp.h>
#include <uapi/linux/tcp.h>
#include <uapi/linux/virtio_net.h>
@@ -48,6 +51,146 @@ static inline int virtio_net_hdr_set_proto(struct sk_buff
*skb,
return 0;
}
+/* TODO: nothing virtio specific here, move to ip.h */
+
+/*
+ * Pull and minimally validate the IPv4 header at @nhoff.
+ * Returns the header and stores the transport header offset in
+ * @thoff, or NULL if truncated or malformed. The whole header,
+ * options included, is guaranteed linear on return.
+ */
+static inline struct iphdr *virtio_net_ip4_parse(struct sk_buff *skb,
+ unsigned int nhoff,
+ unsigned int *thoff)
+{
+ unsigned int ihl;
+ struct iphdr *iph;
+
+ if (!pskb_may_pull(skb, nhoff + sizeof(struct iphdr)))
+ return NULL;
+
+ iph = (struct iphdr *)(skb->data + nhoff);
+ if (iph->version != 4 ||
+ iph->ihl < sizeof(struct iphdr) / sizeof(u32))
+ return NULL;
+
+ ihl = iph->ihl * sizeof(u32);
+ *thoff = nhoff + ihl;
+ /* Pull the options as well: the transport header offset
+ * returned above must be within the linear data. iph goes
+ * stale across the pull.
+ */
+ if (!pskb_may_pull(skb, nhoff + ihl))
+ return NULL;
+
+ return (struct iphdr *)(skb->data + nhoff);
+}
+
+/* Where does the L3 header start, and what protocol is it?
+ * Handles Ethernet and VLAN headers; other devices use the
+ * network header offset the caller set up.
+ */
+static inline bool
+virtio_net_l3_start(struct sk_buff *skb, int *nhoff, __be16 *proto)
+{
+ /* skb->dev should always be set here already,
+ * but let's not crash when it is not.
+ */
+ if (WARN_ON_ONCE(!skb->dev))
+ return false;
+
+ if (skb->dev->type == ARPHRD_ETHER ||
+ skb->dev->type == ARPHRD_LOOPBACK) {
+ __be16 h_proto;
+
+ if (!pskb_may_pull(skb, ETH_HLEN))
+ return false;
+ h_proto = eth_hdr(skb)->h_proto;
+ /* skb->protocol is a sender claim, and parts of the
+ * stack parse the packet per it: when it disagrees with
+ * the frame we do not know which view the packet will
+ * be parsed as, so do not validate.
+ */
+ if (skb->protocol && skb->protocol != h_proto)
+ return false;
+ *nhoff = ETH_HLEN;
+ *proto = h_proto;
+ if (eth_type_vlan(*proto)) {
+ *proto = __vlan_get_protocol(skb, *proto, nhoff);
+ if (!*proto)
+ return false;
+ }
+ } else {
+ const struct iphdr *iph;
+
+ *nhoff = skb_network_offset(skb);
+ /* An unset network header shows up as an offset
+ * outside of the packet.
+ */
+ if (*nhoff < 0 || (unsigned int)*nhoff >= skb->len)
+ return false;
+ /* No L2 header to cross-check with: take the protocol
+ * from the IP version at the network header.
+ */
+ if (!pskb_may_pull(skb, *nhoff + 1))
+ return false;
+ iph = (const struct iphdr *)(skb->data + *nhoff);
+ if (iph->version == 4)
+ *proto = htons(ETH_P_IP);
+ else if (iph->version == 6)
+ *proto = htons(ETH_P_IPV6);
+ else
+ return false;
+ if (skb->protocol && skb->protocol != *proto)
+ return false;
+ }
+ return true;
+}
+
+/* Walk the L3 header at @nhoff: where does its transport header
+ * start, and which protocol is it? Returns false if the header
+ * is truncated, malformed or fragmented.
+ */
+static inline bool
+virtio_net_l4_start(struct sk_buff *skb, unsigned int nhoff, __be16 proto,
+ unsigned int *thoff, int *ip_proto)
+{
+ if (proto == htons(ETH_P_IP)) {
+ const struct iphdr *iph = virtio_net_ip4_parse(skb, nhoff,
thoff);
+
+ if (!iph || ip_is_fragment(iph))
+ return false;
+ *ip_proto = iph->protocol;
+ return true;
+ }
+
+ if (proto == htons(ETH_P_IPV6)) {
+ const struct ipv6hdr *iph;
+ int flags = IP6_FH_F_AUTH;
+
+ if (!pskb_may_pull(skb, nhoff + sizeof(*iph)))
+ return false;
+ iph = (const void *)(skb->data + nhoff);
+ if (iph->version != 6)
+ return false;
+ *thoff = nhoff + sizeof(*iph);
+ *ip_proto = iph->nexthdr;
+ if (*ip_proto != IPPROTO_TCP && *ip_proto != IPPROTO_UDP) {
+ *thoff = nhoff;
+ /* Find the transport header behind any
+ * extension headers, AH included.
+ */
+ *ip_proto = ipv6_find_hdr(skb, thoff, -1, NULL,
+ &flags);
+ if (*ip_proto < 0 || flags & IP6_FH_F_FRAG)
+ return false;
+ }
+ return true;
+ }
+
+ return false;
+}
+
static inline int __virtio_net_hdr_to_skb(struct sk_buff *skb,
const struct virtio_net_hdr *hdr,
bool little_endian, u8 hdr_gso_type)
@@ -282,6 +425,29 @@ static inline unsigned int virtio_l3min(bool is_ipv6)
return is_ipv6 ? sizeof(struct ipv6hdr) : sizeof(struct iphdr);
}
+/* Do the tunnel offsets match the outer headers in the frame?
+ * The L3 header the tunnel claims must be the one the frame
+ * carries, with UDP following it at @outer_th.
+ */
+static inline bool
+virtio_net_tnl_offsets_ok(struct sk_buff *skb, bool outer_isv6,
+ unsigned int outer_th)
+{
+ int nhoff;
+ __be16 proto;
+ unsigned int thoff;
+ int ip_proto;
+
+ if (!virtio_net_l3_start(skb, &nhoff, &proto))
+ return false;
+ if (outer_isv6 != (proto == htons(ETH_P_IPV6)))
+ return false;
+ if (!virtio_net_l4_start(skb, nhoff, proto, &thoff, &ip_proto))
+ return false;
+
+ return ip_proto == IPPROTO_UDP && outer_th == thoff;
+}
+
static inline int
virtio_net_hdr_tnl_to_skb(struct sk_buff *skb,
const struct virtio_net_hdr_v1_hash_tunnel *vhdr,
@@ -338,6 +504,9 @@ virtio_net_hdr_tnl_to_skb(struct sk_buff *skb,
if (ret)
return ret;
+ if (!virtio_net_tnl_offsets_ok(skb, outer_isv6, outer_th))
+ return -EINVAL;
+
/* In case of USO, the inner protocol is still unknown and
* `inner_isv6` is just a guess, additional parsing is needed.
* The previous validation ensures that accessing an ipv4 inner
--
2.53.0
