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@xxxxxxxxxx>
Reviewed-by: Tariq Toukan <tariqt@xxxxxxxxxx>
---
net/core/filter.c | 17 +++-
.../bpf/test_tcp_check_syncookie_user.c | 78 ++++++++++++++-----
2 files changed, 72 insertions(+), 23 deletions(-)
v2 changes: moved from bpf-next to bpf.
v3 changes: added a selftest.
v4 changes: none, CCed Jakub and Arthur from Cloudflare.
diff --git a/net/core/filter.c b/net/core/filter.c
index a7044e98765e..64470a727ef7 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -7016,24 +7016,33 @@ 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 */
diff --git a/tools/testing/selftests/bpf/test_tcp_check_syncookie_user.c b/tools/testing/selftests/bpf/test_tcp_check_syncookie_user.c
index b9e991d43155..e7775d3bbe08 100644
--- a/tools/testing/selftests/bpf/test_tcp_check_syncookie_user.c
+++ b/tools/testing/selftests/bpf/test_tcp_check_syncookie_user.c
@@ -18,8 +18,9 @@
#include "bpf_rlimit.h"
#include "cgroup_helpers.h"
-static int start_server(const struct sockaddr *addr, socklen_t len)
+static int start_server(const struct sockaddr *addr, socklen_t len, bool dual)
{
+ int mode = !dual;
int fd;
fd = socket(addr->sa_family, SOCK_STREAM, 0);
@@ -28,6 +29,14 @@ static int start_server(const struct sockaddr *addr, socklen_t len)
goto out;
}
+ if (addr->sa_family == AF_INET6) {
+ if (setsockopt(fd, IPPROTO_IPV6, IPV6_V6ONLY, (char *)&mode,
+ sizeof(mode)) == -1) {
+ log_err("Failed to set the dual-stack mode");
+ goto close_out;
+ }
+ }
+
if (bind(fd, addr, len) == -1) {
log_err("Failed to bind server socket");
goto close_out;
@@ -47,24 +56,17 @@ static int start_server(const struct sockaddr *addr, socklen_t len)
return fd;
}
-static int connect_to_server(int server_fd)
+static int connect_to_server(const struct sockaddr *addr, socklen_t len)
{
- struct sockaddr_storage addr;
- socklen_t len = sizeof(addr);
int fd = -1;
- if (getsockname(server_fd, (struct sockaddr *)&addr, &len)) {
- log_err("Failed to get server addr");
- goto out;
- }
-
- fd = socket(addr.ss_family, SOCK_STREAM, 0);
+ fd = socket(addr->sa_family, SOCK_STREAM, 0);
if (fd == -1) {
log_err("Failed to create client socket");
goto out;
}
- if (connect(fd, (const struct sockaddr *)&addr, len) == -1) {
+ if (connect(fd, (const struct sockaddr *)addr, len) == -1) {
log_err("Fail to connect to server");
goto close_out;
}
@@ -116,7 +118,8 @@ static int get_map_fd_by_prog_id(int prog_id, bool *xdp)
return map_fd;
}
-static int run_test(int server_fd, int results_fd, bool xdp)
+static int run_test(int server_fd, int results_fd, bool xdp,
+ const struct sockaddr *addr, socklen_t len)
{
int client = -1, srv_client = -1;
int ret = 0;
@@ -142,7 +145,7 @@ static int run_test(int server_fd, int results_fd, bool xdp)
goto err;
}
- client = connect_to_server(server_fd);
+ client = connect_to_server(addr, len);
if (client == -1)
goto err;
@@ -199,12 +202,30 @@ static int run_test(int server_fd, int results_fd, bool xdp)
return ret;
}
+static bool get_port(int server_fd, in_port_t *port)
+{
+ struct sockaddr_in addr;
+ socklen_t len = sizeof(addr);
+
+ if (getsockname(server_fd, (struct sockaddr *)&addr, &len)) {
+ log_err("Failed to get server addr");
+ return false;
+ }
+
+ /* sin_port and sin6_port are located at the same offset. */
+ *port = addr.sin_port;
+ return true;
+}
+
int main(int argc, char **argv)
{
struct sockaddr_in addr4;
struct sockaddr_in6 addr6;
+ struct sockaddr_in addr4dual;
+ struct sockaddr_in6 addr6dual;
int server = -1;
int server_v6 = -1;
+ int server_dual = -1;
int results = -1;
int err = 0;
bool xdp;
@@ -224,25 +245,43 @@ int main(int argc, char **argv)
addr4.sin_family = AF_INET;
addr4.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
addr4.sin_port = 0;
+ memcpy(&addr4dual, &addr4, sizeof(addr4dual));
memset(&addr6, 0, sizeof(addr6));
addr6.sin6_family = AF_INET6;
addr6.sin6_addr = in6addr_loopback;
addr6.sin6_port = 0;
- server = start_server((const struct sockaddr *)&addr4, sizeof(addr4));
- if (server == -1)
+ memset(&addr6dual, 0, sizeof(addr6dual));
+ addr6dual.sin6_family = AF_INET6;
+ addr6dual.sin6_addr = in6addr_any;
+ addr6dual.sin6_port = 0;
+
+ server = start_server((const struct sockaddr *)&addr4, sizeof(addr4),
+ false);
+ if (server == -1 || !get_port(server, &addr4.sin_port))
goto err;
server_v6 = start_server((const struct sockaddr *)&addr6,
- sizeof(addr6));
- if (server_v6 == -1)
+ sizeof(addr6), false);
+ if (server_v6 == -1 || !get_port(server_v6, &addr6.sin6_port))
+ goto err;
+
+ server_dual = start_server((const struct sockaddr *)&addr6dual,
+ sizeof(addr6dual), true);
+ if (server_dual == -1 || !get_port(server_dual, &addr4dual.sin_port))
+ goto err;
+
+ if (run_test(server, results, xdp,
+ (const struct sockaddr *)&addr4, sizeof(addr4)))
goto err;
- if (run_test(server, results, xdp))
+ if (run_test(server_v6, results, xdp,
+ (const struct sockaddr *)&addr6, sizeof(addr6)))
goto err;
- if (run_test(server_v6, results, xdp))
+ if (run_test(server_dual, results, xdp,
+ (const struct sockaddr *)&addr4dual, sizeof(addr4dual)))
goto err;
printf("ok\n");
@@ -252,6 +291,7 @@ int main(int argc, char **argv)
out:
close(server);
close(server_v6);
+ close(server_dual);
close(results);
return err;
}
--
2.30.2
