linux-kernel - [PATCH 5.4 439/475] bpf: Support dual-stack sockets in bpf_tcp_check

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Message-Id: <20220414110907.348077408@linuxfoundation.org>
Date:   Thu, 14 Apr 2022 15:13:44 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Maxim Mikityanskiy <maximmi@...dia.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Tariq Toukan <tariqt@...dia.com>,
        Arthur Fabre <afabre@...udflare.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.4 439/475] bpf: Support dual-stack sockets in bpf_tcp_check_syncookie

From: Maxim Mikityanskiy <maximmi@...dia.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@...dia.com>
Signed-off-by: Alexei Starovoitov <ast@...nel.org>
Reviewed-by: Tariq Toukan <tariqt@...dia.com>
Acked-by: Arthur Fabre <afabre@...udflare.com>
Link: https://lore.kernel.org/bpf/20220406124113.2795730-1-maximmi@nvidia.com
Signed-off-by: Sasha Levin <sashal@...nel.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 54c5e3c379f6..e16b2b5cda98 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -5824,24 +5824,33 @@ 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 */
-- 
2.35.1