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

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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: 217ac77a3c ("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>
This commit is contained in:
Cen Zhang (Microsoft)
2026-07-30 18:20:06 -04:00
committed by Paolo Abeni
parent 1a35da325c
commit cf6f8b29be
1 changed files with 7 additions and 4 deletions
Download Patch File Download Diff File Expand all files Collapse all files

11
net/openvswitch/flow.c
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@@ -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);