From: Maxim Mikityanskiy maximmi@nvidia.com
[ Upstream commit 2e8702cc0cfa1080f29fd64003c00a3e24ac38de ]
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: 399040847084 ("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 --- net/core/filter.c | 17 +++++++++++++---- 1 file changed, 13 insertions(+), 4 deletions(-)
diff --git a/net/core/filter.c b/net/core/filter.c index 4721ed65bcc5..590790c63fa3 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -6719,24 +6719,33 @@ BPF_CALL_5(bpf_tcp_check_syncookie, struct sock *, sk, void *, iph, u32, iph_len if (!th->ack || th->rst || th->syn) return -ENOENT;
+ if (unlikely(iph_len < sizeof(struct iphdr))) + return -EINVAL; + if (tcp_synq_no_recent_overflow(sk)) return -ENOENT;
cookie = ntohl(th->ack_seq) - 1;
- switch (sk->sk_family) { - case AF_INET: - if (unlikely(iph_len < sizeof(struct iphdr))) + /* Both struct iphdr and struct ipv6hdr have the version field at the + * same offset so we can cast to the shorter header (struct iphdr). + */ + switch (((struct iphdr *)iph)->version) { + case 4: + if (sk->sk_family == AF_INET6 && ipv6_only_sock(sk)) return -EINVAL;
ret = __cookie_v4_check((struct iphdr *)iph, th, cookie); break;
#if IS_BUILTIN(CONFIG_IPV6) - case AF_INET6: + case 6: if (unlikely(iph_len < sizeof(struct ipv6hdr))) return -EINVAL;
+ if (sk->sk_family != AF_INET6) + return -EINVAL; + ret = __cookie_v6_check((struct ipv6hdr *)iph, th, cookie); break; #endif /* CONFIG_IPV6 */