net/openvswitch: check Ethernet header length in key_extract()

When a packet arrives on an ARPHRD_NONE device (e.g. TUN),
ovs_flow_key_extract() trusts the user-provided skb->protocol field: if
it is ETH_P_TEB, the packet is classified as MAC_PROTO_ETHERNET and
key_extract() is called without ensuring the skb has ETH_HLEN (14) bytes
of linear data. key_extract() unconditionally pulls 2 * ETH_ALEN bytes
for MAC addresses and parse_ethertype() pulls 2 more, either of which
triggers a kernel BUG in __skb_pull() when the linear area is too small.

  kernel BUG at include/linux/skbuff.h:2848!
  RIP: 0010:key_extract+0xa7e/0xd90 net/openvswitch/flow.c:933
  ovs_flow_key_extract+0x419/0xa70
  ovs_vport_receive+0x222/0x390
  netdev_frame_hook+0x3e0/0x630
  tun_get_user+0x2d0c/0x38e0

Fixed by calling check_header() in key_extract() before accessing the
Ethernet header.

Fixes: 217ac77a3c25 ("openvswitch: allow L3 netdev ports")
Reported-by: AutonomousCodeSecurity@microsoft.com
Reviewed-by: Eelco Chaudron <echaudro@redhat.com>
Signed-off-by: Cen Zhang (Microsoft) <blbllhy@gmail.com>
Reviewed-by: Ilya Maximets <i.maximets@ovn.org>
Link: https://patch.msgid.link/20260730222006.118652-1-blbllhy@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

diff --git a/net/openvswitch/flow.c b/net/openvswitch/flow.c
index 66366982f60446684c789791e20fcfd3335631d0..46c1d66aad8c3d9a5bd7e45df60e79318ca6ee5b 100644 (file)
--- a/net/openvswitch/flow.c
+++ b/net/openvswitch/flow.c
@@ -889,8 +889,6 @@ static int key_extract_l3l4(struct sk_buff *skb, struct sw_flow_key *key)
  * Ethernet header
  * @key: output flow key
  *
- * The caller must ensure that skb->len >= ETH_HLEN.
- *
  * Initializes @skb header fields as follows:
  *
  *    - skb->mac_header: the L2 header.
@@ -910,8 +908,6 @@ static int key_extract_l3l4(struct sk_buff *skb, struct sw_flow_key *key)
  */
 static int key_extract(struct sk_buff *skb, struct sw_flow_key *key)
 {
-       struct ethhdr *eth;
-
        /* Flags are always used as part of stats */
        key->tp.flags = 0;
 
@@ -926,6 +922,13 @@ static int key_extract(struct sk_buff *skb, struct sw_flow_key *key)
                skb_reset_network_header(skb);
                key->eth.type = skb->protocol;
        } else {
+               struct ethhdr *eth;
+               int err;
+
+               err = check_header(skb, ETH_HLEN);
+               if (unlikely(err))
+                       return err;
+
                eth = eth_hdr(skb);
                ether_addr_copy(key->eth.src, eth->h_source);
                ether_addr_copy(key->eth.dst, eth->h_dest);