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 checks in key_extract() before pulling the Ethernet
header.
Fixes: 217ac77a3c25 ("openvswitch: allow L3 netdev ports")
Reported-by: [email protected]
Signed-off-by: Cen Zhang (Microsoft) <[email protected]>
---
v3: Use check_header() per review, fix format issue.
v2: Moved the check into key_extract() per Ilya Maximets.
Link: https://lore.kernel.org/all/[email protected]
net/openvswitch/flow.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/net/openvswitch/flow.c b/net/openvswitch/flow.c
index 66366982f604..fc4002353e17 100644
--- a/net/openvswitch/flow.c
+++ b/net/openvswitch/flow.c
@@ -911,6 +911,7 @@ 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;
+ int err;
/* Flags are always used as part of stats */
key->tp.flags = 0;
@@ -926,6 +927,10 @@ static int key_extract(struct sk_buff *skb, struct
sw_flow_key *key)
skb_reset_network_header(skb);
key->eth.type = skb->protocol;
} else {
+ 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
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