added get_local_ips command

Author: Catalyn45

.gitignore

@@ -0,0 +1,3 @@
+obj/
+netcli
+netcli_test

Makefile

@@ -0,0 +1,53 @@
+PROJNAME=netcli
+TESTNAME=$(PROJNAME)_test
+
+CC=clang
+CXX=clang++
+
+CFLAGS=-fPIC -g -Wall -Wextra -Werror -Winline -MD
+
+LIBS=-lpthread
+TEST_LIBS=-lgtest -lgtest_main
+
+C=$(shell find ./src -name "*.c")
+TEST_CPP=$(shell find ./test -name "*.cpp" 2> /dev/null)
+
+OBJ=$(patsubst %,obj/%.o,$(basename $(C)))
+TEST_OBJ=$(patsubst %,obj/%.o,$(basename $(TEST_CPP)))
+
+default: all
+
+obj/./src/%.o: src/%.c
+	@mkdir -p $(@D)
+	@echo -e "\033[0;32mCompiling $<"
+	@$(CC) $(CFLAGS) -c $< -o $@
+
+obj/./test/%.o: test/%.cpp
+	@mkdir -p $(@D)
+	@echo -e "\033[0;32mCompiling $<"
+	@$(CXX) $(CFLAGS) -I . -c $< -o $@
+
+$(PROJNAME): $(OBJ) 
+	@echo -e "\033[0;36mLinking $@"
+	@$(CC) $(CFLAGS) -o $@ $^ $(LIBS)
+	@echo -e "\033[0;35mSrc done"
+
+$(TESTNAME): $(TEST_OBJ) $(filter-out obj/./src/main.o, $(OBJ))
+	@echo -e "\033[0;36mLinking $@"
+	@$(CXX) $(CFLAGS) -o $(TESTNAME) $^ $(LIBS) $(TEST_LIBS)
+	@echo -e "\033[0;35mTest done"
+
+all: $(PROJNAME) $(PROJNAME)_test
+	@echo -e "\033[0;37mAll done"
+
+clean:
+	@echo -e "\033[1;33mCleaning up"
+	@rm $(PROJNAME) -f
+	@rm $(TESTNAME) -f
+	@rm $(OBJ) -f
+	@rm $(patsubst %.o, %.d, $(OBJ))
+	@rm $(TEST_OBJ) -f
+	@rm $(patsubst %.o, %.d, $(TEST_OBJ))
+
+-include $(OBJ:.o=.d)
+-include $(TEST_OBJ:.o=.d)

README.md

@@ -1 +1,3 @@
 # net-cli
+
+project for learning to interract with the kernel through the netlink interface

src/commands.c

@@ -0,0 +1,133 @@
+#include "commands.h"
+#include <linux/netlink.h>
+#include <linux/rtnetlink.h>
+#include <arpa/inet.h>
+#include <unistd.h>
+#include <stdlib.h>
+
+
+static int netlink_route(struct sockaddr_nl* out_sa) {
+    // create the netlink socket with the NETLINK_ROUTE protocol
+    int fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE);
+    if (fd < 0)
+        return -1;
+
+    // create the netlink sockaddr
+    *out_sa = (struct sockaddr_nl) {
+        .nl_family = AF_NETLINK
+    };
+
+    // bind the file descriptor to the address
+    int res = bind(fd, (const struct sockaddr*)out_sa, sizeof(*out_sa));
+    if (res != 0) {
+        close(fd);
+        return -1;
+    }
+
+    return fd;
+}
+
+
+int get_local_ips(int family, ip_callback_t callback, void* args) {
+    struct sockaddr_nl sa;
+    int fd = netlink_route(&sa);
+    if (fd == -1)
+        return -1;
+
+    // calculate the total buffer length
+    const size_t buffer_length = NLMSG_ALIGN(NLMSG_LENGTH(sizeof(struct ifaddrmsg)));
+    unsigned char buffer[buffer_length];
+
+    // create the header of the message
+    struct nlmsghdr* nlh = (void*)buffer;
+    *nlh = (struct nlmsghdr){
+        .nlmsg_len = buffer_length,
+        .nlmsg_type = RTM_GETADDR,
+        .nlmsg_flags = NLM_F_REQUEST | NLM_F_ROOT
+    };
+
+    // create the payload of the message
+    struct ifaddrmsg* ifa = NLMSG_DATA(nlh);
+    *ifa = (struct ifaddrmsg){
+        .ifa_family = family
+    };
+
+    // create the iovec structure containing the buffer and length
+    struct iovec iov = {
+        .iov_base = buffer,
+        .iov_len = buffer_length
+    };
+
+    // create the message header structure
+    struct msghdr msg = {
+        .msg_name = &sa,
+        .msg_namelen = sizeof(sa),
+        .msg_iov = &iov,
+        .msg_iovlen = 1
+    };
+
+    // send the message to kernel
+    ssize_t sent = sendmsg(fd, &msg, 0);
+    if (sent < 0)
+        goto close_fd;
+
+    iov.iov_len = 0;
+
+    // peek the data to see how many bytes are there to read
+    ssize_t received = recvmsg(fd, &msg, MSG_PEEK | MSG_TRUNC);
+    if (received < 0)
+        goto close_fd;
+
+    size_t len = (size_t)received;
+
+    // allocate the needed memory
+    unsigned char* recv_buffer = malloc(len);
+    if (!recv_buffer)
+        goto close_fd;
+
+    iov.iov_base = (void*)recv_buffer;
+    iov.iov_len = len;
+
+    // receive the actual messages
+    received = recvmsg(fd, &msg, 0);
+    if (received < 0)
+        goto free_buf;
+
+    len = (size_t)received;
+
+    // iterate from every message available
+    for (nlh = (void*)recv_buffer; NLMSG_OK(nlh, len); nlh = NLMSG_NEXT(nlh, len)) {
+        struct ifaddrmsg* ifa = (void*)NLMSG_DATA(nlh);
+
+        size_t rta_len = IFA_PAYLOAD(nlh);
+
+        // iterate from every attribute of the message
+        for (struct rtattr* rta = (void*)IFA_RTA(ifa); RTA_OK(rta, rta_len); rta = RTA_NEXT(rta, rta_len)) {
+            // if the attribute is an address, create the structure
+            // and call the callback provided by the user
+            if (rta->rta_type == IFA_ADDRESS) {
+                struct ip_entry entry = {
+                    .addr = *((struct sockaddr*)RTA_DATA(rta)),
+                    .index = ifa->ifa_index,
+                    .family = family
+                };
+
+                callback(&entry, args);
+            }
+        }
+    }
+
+    free(recv_buffer);
+
+    close(fd);
+
+    return 0;
+
+free_buf:
+    free(recv_buffer);
+
+close_fd:
+    close(fd);
+
+    return -1;
+}

src/commands.h

@@ -0,0 +1,18 @@
+#ifndef COMMANDS_H
+#define COMMANDS_H
+
+#include <sys/socket.h>
+#include <stdint.h>
+
+struct ip_entry {
+    struct sockaddr addr;
+    uint16_t index;
+    int family;
+};
+
+typedef int (*ip_callback_t)(struct ip_entry* adr, void* args);
+
+// all the local ips for every interface
+int get_local_ips(int family, ip_callback_t callback, void* args);
+
+#endif

src/main.c

@@ -0,0 +1,30 @@
+#include <sys/socket.h>
+#include <stdlib.h>
+#include <arpa/inet.h>
+#include <net/if.h>
+#include <stdio.h>
+
+#include "commands.h"
+
+int ip_callback(struct ip_entry* addr, void* args) {
+    (void)args;
+
+    char ip[INET_ADDRSTRLEN];
+    inet_ntop(AF_INET, &addr->addr, ip, sizeof(ip));
+
+    char interface[IF_NAMESIZE];
+    printf("%s -> ip: %s\n", if_indextoname(addr->index, interface), ip);
+
+    return 0;
+}
+
+int main(int argc, char **argv) {
+    (void)argv;
+    (void)argc;
+
+    if (get_local_ips(AF_INET, ip_callback, NULL) != 0) {
+        return -1;
+    }
+
+    return 0;
+}