how to initialize a buffer - c

Question

This is my server/client sockets code.
I have a problem with the buffer, when the client receives the message from the server which is the buffer (i initialized it to "12") the output shows like this:
[+]Client Socket is created.
[+]Connected to Server.
Temp :
12121212121212121212121212121212121212121212121212121212121212121212121212121212
12121212121212�L��Q�
server :
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#define PORT 4444
int main(){
int sockfd, ret;
struct sockaddr_in serverAddr;
int clientSocket;
struct sockaddr_in newAddr;
socklen_t addr_size;
char buffer[1024];
char Temp[4]= "12";
pid_t childpid;
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if(sockfd < 0){
printf("[-]Error in connection.\n");
exit(1);
}
printf("[+]Server Socket is created.\n");
memset(&serverAddr, '\0', sizeof(serverAddr));
serverAddr.sin_family = AF_INET;
serverAddr.sin_port = htons(PORT);
serverAddr.sin_addr.s_addr = inet_addr("127.0.0.1");
ret = bind(sockfd, (struct sockaddr*)&serverAddr, sizeof(serverAddr));
if(ret < 0){
printf("[-]Error in binding.\n");
exit(1);
}
printf("[+]Bind to port %d\n", 4444);
if(listen(sockfd, 10) == 0){
printf("[+]Listening....\n");
}else{
printf("[-]Error in binding.\n");
}
while(1){
clientSocket = accept(sockfd, (struct sockaddr*)&newAddr, &addr_size);
if(clientSocket < 0){
exit(1);
}
printf("Connection accepted from %s:%d\n", inet_ntoa(newAddr.sin_addr),
ntohs(newAddr.sin_port));
if((childpid = fork()) == 0){
close(sockfd);
while(1){
send(clientSocket, Temp, strlen(Temp), 0);
bzero(buffer, sizeof(buffer));
if(strcmp(Temp, ":exit") == 0){
printf("Disconnected from %s:%d\n",
inet_ntoa(newAddr.sin_addr), ntohs(newAddr.sin_port));
break;
}
}
}
}
return 0;
}
client :
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#define PORT 4444
int main(){
int clientSocket, ret;
struct sockaddr_in serverAddr;
char buffer[1024];
char Temp[4];
clientSocket = socket(AF_INET, SOCK_STREAM, 0);
if(clientSocket < 0){
printf("[-]Error in connection.\n");
exit(1);
}
printf("[+]Client Socket is created.\n");
memset(&serverAddr, '\0', sizeof(serverAddr));
serverAddr.sin_family = AF_INET;
serverAddr.sin_port = htons(PORT);
serverAddr.sin_addr.s_addr = inet_addr("127.0.0.1");
ret = connect(clientSocket, (struct sockaddr*)&serverAddr,
sizeof(serverAddr));
if(ret < 0){
printf("[-]Error in connection.\n");
exit(1);
}
printf("[+]Connected to Server.\n");
bzero(buffer,512);
int words = 0;
char c;
while(1){
recv(clientSocket, Temp, 1024, 0);
if(recv(clientSocket, Temp, 1024, 0) < 0){
printf("[-]Error in receiving data.\n");
}
printf("Temp : %s \n",Temp);
if(strcmp(Temp, ":exit") == 0){
close(clientSocket);
printf("[-]Disconnected from server.\n");
} exit(1);
}
return 0;
}
Please, can anyone tell me how can I solve this problem, any help would be appreciated.

Answer 1

I see several problems with your client code:
char Temp[4];
...
recv(clientSocket, Temp, 1024, 0);
Here you are reading up to 1024 bytes into Temp although only 4 bytes are allocated for Temp. If you read more than 4 bytes thus other data structures will be filled with the read data, i.e. a classic buffer overflow.
printf("Temp : %s \n",Temp);
Here you are assuming that Temp is a \0 terminated string, which it is not. Therefore it will print out data starting with the position of &Temp up to a \0 byte it will find somewhere (way outside of Temp based on your output).
if(strcmp(Temp, ":exit") == 0){
Even though Temp is only 4 bytes this statement assumes at least 6 bytes (5 byte string and \0 for end of string marker).
Similar problems are also at the server code. Also strange is that your buffer variable is initialized but otherwise never used. My guess is that you originally wanted to use this instead of Temp for sending and receiving.