From cf9b1199de27ece1eafacf165933df10f0314232 Mon Sep 17 00:00:00 2001 From: Sargun Dhillon Date: Mon, 25 Jul 2016 05:55:02 -0700 Subject: samples/bpf: Add test/example of using bpf_probe_write_user bpf helper This example shows using a kprobe to act as a dnat mechanism to divert traffic for arbitrary endpoints. It rewrite the arguments to a syscall while they're still in userspace, and before the syscall has a chance to copy the argument into kernel space. Although this is an example, it also acts as a test because the mapped address is 255.255.255.255:555 -> real address, and that's not a legal address to connect to. If the helper is broken, the example will fail on the intermediate steps, as well as the final step to verify the rewrite of userspace memory succeeded. Signed-off-by: Sargun Dhillon Cc: Alexei Starovoitov Cc: Daniel Borkmann Acked-by: Alexei Starovoitov Signed-off-by: David S. Miller --- samples/bpf/test_probe_write_user_user.c | 78 ++++++++++++++++++++++++++++++++ 1 file changed, 78 insertions(+) create mode 100644 samples/bpf/test_probe_write_user_user.c (limited to 'samples/bpf/test_probe_write_user_user.c') diff --git a/samples/bpf/test_probe_write_user_user.c b/samples/bpf/test_probe_write_user_user.c new file mode 100644 index 000000000000..a44bf347bedd --- /dev/null +++ b/samples/bpf/test_probe_write_user_user.c @@ -0,0 +1,78 @@ +#include +#include +#include +#include +#include "libbpf.h" +#include "bpf_load.h" +#include +#include +#include +#include + +int main(int ac, char **argv) +{ + int serverfd, serverconnfd, clientfd; + socklen_t sockaddr_len; + struct sockaddr serv_addr, mapped_addr, tmp_addr; + struct sockaddr_in *serv_addr_in, *mapped_addr_in, *tmp_addr_in; + char filename[256]; + char *ip; + + serv_addr_in = (struct sockaddr_in *)&serv_addr; + mapped_addr_in = (struct sockaddr_in *)&mapped_addr; + tmp_addr_in = (struct sockaddr_in *)&tmp_addr; + + snprintf(filename, sizeof(filename), "%s_kern.o", argv[0]); + + if (load_bpf_file(filename)) { + printf("%s", bpf_log_buf); + return 1; + } + + assert((serverfd = socket(AF_INET, SOCK_STREAM, 0)) > 0); + assert((clientfd = socket(AF_INET, SOCK_STREAM, 0)) > 0); + + /* Bind server to ephemeral port on lo */ + memset(&serv_addr, 0, sizeof(serv_addr)); + serv_addr_in->sin_family = AF_INET; + serv_addr_in->sin_port = 0; + serv_addr_in->sin_addr.s_addr = htonl(INADDR_LOOPBACK); + + assert(bind(serverfd, &serv_addr, sizeof(serv_addr)) == 0); + + sockaddr_len = sizeof(serv_addr); + assert(getsockname(serverfd, &serv_addr, &sockaddr_len) == 0); + ip = inet_ntoa(serv_addr_in->sin_addr); + printf("Server bound to: %s:%d\n", ip, ntohs(serv_addr_in->sin_port)); + + memset(&mapped_addr, 0, sizeof(mapped_addr)); + mapped_addr_in->sin_family = AF_INET; + mapped_addr_in->sin_port = htons(5555); + mapped_addr_in->sin_addr.s_addr = inet_addr("255.255.255.255"); + + assert(!bpf_update_elem(map_fd[0], &mapped_addr, &serv_addr, BPF_ANY)); + + assert(listen(serverfd, 5) == 0); + + ip = inet_ntoa(mapped_addr_in->sin_addr); + printf("Client connecting to: %s:%d\n", + ip, ntohs(mapped_addr_in->sin_port)); + assert(connect(clientfd, &mapped_addr, sizeof(mapped_addr)) == 0); + + sockaddr_len = sizeof(tmp_addr); + ip = inet_ntoa(tmp_addr_in->sin_addr); + assert((serverconnfd = accept(serverfd, &tmp_addr, &sockaddr_len)) > 0); + printf("Server received connection from: %s:%d\n", + ip, ntohs(tmp_addr_in->sin_port)); + + sockaddr_len = sizeof(tmp_addr); + assert(getpeername(clientfd, &tmp_addr, &sockaddr_len) == 0); + ip = inet_ntoa(tmp_addr_in->sin_addr); + printf("Client's peer address: %s:%d\n", + ip, ntohs(tmp_addr_in->sin_port)); + + /* Is the server's getsockname = the socket getpeername */ + assert(memcmp(&serv_addr, &tmp_addr, sizeof(struct sockaddr_in)) == 0); + + return 0; +} -- cgit v1.2.3-59-g8ed1b