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 Reviewed-by: Tariq Toukan tariqt@nvidia.com Acked-by: Arthur Fabre afabre@cloudflare.com --- 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 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 */
The previous commit fixed support for dual-stack sockets in bpf_tcp_check_syncookie. This commit adjusts the selftest to verify the fixed functionality.
Signed-off-by: Maxim Mikityanskiy maximmi@nvidia.com Acked-by: Arthur Fabre afabre@cloudflare.com --- .../bpf/test_tcp_check_syncookie_user.c | 78 ++++++++++++++----- 1 file changed, 59 insertions(+), 19 deletions(-)
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; }
Hello:
This series was applied to bpf/bpf.git (master) by Alexei Starovoitov ast@kernel.org:
On Wed, 6 Apr 2022 15:41:12 +0300 you wrote:
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:
[...]
Here is the summary with links: - [bpf,v5,1/2] bpf: Support dual-stack sockets in bpf_tcp_check_syncookie https://git.kernel.org/bpf/bpf/c/2e8702cc0cfa - [bpf,v5,2/2] bpf: Adjust bpf_tcp_check_syncookie selftest to test dual-stack sockets https://git.kernel.org/bpf/bpf/c/53968dafc4a6
You are awesome, thank you!
linux-kselftest-mirror@lists.linaro.org
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Maxim Mikityanskiy -
patchwork-bot+netdevbpf＠kernel.org