bpf: Support dual-stack sockets in bpf_tcp_check_syncookie
[ Upstream commit 2e8702cc ] bpf_tcp_gen_syncookie looks at the IP version in the IP header and validates the address family of the socket. It supports IPv4 packets in AF_INET6 dual-stack sockets. On the other hand, bpf_tcp_check_syncookie looks only at the address family of the socket, ignoring the real IP version in headers, and validates only the packet size. This implementation has some drawbacks: 1. Packets are not validated properly, allowing a BPF program to trick bpf_tcp_check_syncookie into handling an IPv6 packet on an IPv4 socket. 2. Dual-stack sockets fail the checks on IPv4 packets. IPv4 clients end up receiving a SYNACK with the cookie, but the following ACK gets dropped. This patch fixes these issues by changing the checks in bpf_tcp_check_syncookie to match the ones in bpf_tcp_gen_syncookie. IP version from the header is taken into account, and it is validated properly with address family. Fixes: 39904084 ("bpf: add helper to check for a valid SYN cookie") Signed-off-by: Maxim Mikityanskiy <maximmi@nvidia.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Reviewed-by: Tariq Toukan <tariqt@nvidia.com> Acked-by: Arthur Fabre <afabre@cloudflare.com> Link: https://lore.kernel.org/bpf/20220406124113.2795730-1-maximmi@nvidia.com Signed-off-by: Sasha Levin <sashal@kernel.org>
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