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 Signed-off-by: Cen Zhang (Microsoft) --- v5: Separate err declaration and initialization per review. v4: Update documentation and move variables into the Ethernet block. v3: Use check_header() per review, fix format issue. v2: Moved the check into key_extract() per Ilya Maximets. Link: https://lore.kernel.org/r/20260725043128.193164-1-blbllhy@gmail.com net/openvswitch/flow.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/net/openvswitch/flow.c b/net/openvswitch/flow.c index 66366982f604..46c1d66aad8c 100644 --- 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); -- 2.53.0