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(+)
diff --git a/net/openvswitch/flow.c b/net/openvswitch/flow.c
index 66366982f604..a0f9d788d284 100644
--- a/net/openvswitch/flow.c
+++ b/net/openvswitch/flow.c
@@ -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);
--
2.53.0
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