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

PATCH Superseded Cen Zhang (Microsoft) 2 participants 2 messages Jul 21 – Jul 22

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Networking Network drivers Openvswitch

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Cen Zhang (Microsoft)

author

2026-07-21 14:36 UTC #0 lore raw

PATCH 1/1 net/openvswitch: check Ethernet header length before 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 adding check_header(skb, ETH_HLEN) in ovs_flow_key_extract() before calling key_extract().

Fixes 217ac77a3c25 ("openvswitch: allow L3 netdev ports")

Reported-by [email protected]

Signed-off-by Cen Zhang (Microsoft) <[email protected]>

---
 net/openvswitch/flow.c | 7 +++++++
 1 file changed, 7 insertions(+)

net/openvswitch/flow.c +7 -0

index 66366982f604..a0f9d788d284 100644
@@ -1035,6 +1035,13 @@ int ovs_flow_key_extract(const struct ip_tunnel_info *tun_info,
 		return res;
 	key->mac_proto = res;
 
+	if (res == MAC_PROTO_ETHERNET) {
+		int err = check_header(skb, ETH_HLEN);
+
+		if (unlikely(err))
+			return err;
+	}
+
 #if IS_ENABLED(CONFIG_NET_TC_SKB_EXT)
 	if (tc_skb_ext_tc_enabled()) {
 		tc_ext = skb_ext_find(skb, TC_SKB_EXT);

Signature · 1 line

2.53.0

Ilya Maximets

maintainer

2026-07-22 11:58 UTC #1 lore raw

Quoted 30 lines · Cen Zhang (Microsoft)

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 adding check_header(skb, ETH_HLEN) in ovs_flow_key_extract() before calling key_extract().
Fixes 217ac77a3c25 ("openvswitch: allow L3 netdev ports")
Reported-by [email protected]
Signed-off-by Cen Zhang (Microsoft) <[email protected]>
---
 net/openvswitch/flow.c | 7 +++++++
 1 file changed, 7 insertions(+)
net/openvswitch/flow.c +0 -0
index 66366982f604..a0f9d788d284 100644

net/openvswitch/flow.c int ovs_flow_key_extract(const struct ip_tunnel_info *tun_info, · line 1043

Quoted 9 lines

net/openvswitch/flow.c +6 -0

@@ -1035,6 +1035,13 @@ int ovs_flow_key_extract(const struct ip_tunnel_info *tun_info,
 		return res;
 	key->mac_proto = res;
 
+	if (res == MAC_PROTO_ETHERNET) {
+		int err = check_header(skb, ETH_HLEN);
+
+		if (unlikely(err))
+			return err;
+	}

I'd suggest moving this check closer to the place where we're pulling the header, i.e. into the key_extract() function itself.

Best regards, Ilya Maximets.