# \[PATCH 1/3\] openvswitch: Add length check when retrieving TCP flags. - From: Jesse Gross \ - Date: 2012-05-08 01:51:23 - List: netdev - Page: https://ratatoskr.run/netdev/2012/05/10894716 - Thread: https://ratatoskr.run/netdev/2012/05/10894716/t.md ```text When collecting TCP flags we check that the IP header indicates that a TCP header is present but not that the packet is actually long enough to contain the header. This adds a check to prevent reading off the end of the packet. In practice, this is only likely to result in reading of bad data and not a crash due to the presence of struct skb_shared_info at the end of the packet. Signed-off-by: Jesse Gross --- net/openvswitch/flow.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/net/openvswitch/flow.c b/net/openvswitch/flow.c index 1252c30..2a11ec2 100644 --- a/net/openvswitch/flow.c +++ b/net/openvswitch/flow.c @@ -183,7 +183,8 @@ void ovs_flow_used(struct sw_flow *flow, struct sk_buff *skb) u8 tcp_flags = 0; if (flow->key.eth.type == htons(ETH_P_IP) && - flow->key.ip.proto == IPPROTO_TCP) { + flow->key.ip.proto == IPPROTO_TCP && + likely(skb->len >= skb_transport_offset(skb) + sizeof(struct tcphdr))) { u8 *tcp = (u8 *)tcp_hdr(skb); tcp_flags = *(tcp + TCP_FLAGS_OFFSET) & TCP_FLAG_MASK; } -- 1.7.9.5 ```