Multipleclient Server: quitfunction - c

Question

I have some problems with my Server/Client.
If multiple people connect to my server, and one of them quit the connection to the server, all other, which are also connected to the server, lose their connection to.
void *connection_handler(void *);
extern int check_err_buffer(int sock);
extern error_t *error_buffer;
extern invalid_user_input_t invalid_user_input;
regex_t regex;
int main(int argc, char *argv[]) {
//init KVS
init();
int socket_desc, client_sock, c, *new_sock;
struct sockaddr_in server, client;
//Create socket
socket_desc = socket(AF_INET, SOCK_STREAM | O_NONBLOCK, 0);
int opts;
opts = fcntl(socket_desc,F_GETFL);
opts = opts & (~O_NONBLOCK);
fcntl(socket_desc,F_SETFL,opts);
if (socket_desc == -1) {
printf("Could not create socket");
}
puts("Socket created");
//Prepare the sockaddr_in structure
server.sin_family = AF_INET;
server.sin_addr.s_addr = INADDR_ANY;
server.sin_port = htons(8503);
//Bind
if (bind(socket_desc, (struct sockaddr *) &server, sizeof(server)) < 0) {
//print the error message
perror("bind failed. Error");
return 1;
}
puts("bind done");
//Listen
listen(socket_desc, 3);
//Accept and incoming connection
puts("Waiting for incoming connections...");
c = sizeof(struct sockaddr_in);//Accept and incoming connection
puts("Waiting for incoming connections...");
c = sizeof(struct sockaddr_in);
while (1) {
puts("waiting for client...");
client_sock = accept(socket_desc, (struct sockaddr *) &client, (socklen_t * ) & c);
puts("Connection accepted");
pthread_t sniffer_thread;
new_sock = malloc(1);
*new_sock = client_sock;
pthread_create(&sniffer_thread, NULL, connection_handler, (void *) new_sock);
//Now join the thread , so that we dont terminate before the thread
//pthread_join(sniffer_thread, NULL);
puts("Handler assigned");
}
if (client_sock < 0) {
perror("accept failed");
return 1;
}
return 0;
}
In the main function I accept the different connection from the clients.
I have more functions, which I didn't put in, because they are not so relevant for this problem.
In the second part I will handle some cases. I look if the client type the letter 'q', if it's true, I will close the connection with close().
But in all cases, it close the server, and all connections are lost.
/*
* This will handle connection for each client
* */
void *connection_handler(void *socket_desc) {
//Get the socket descriptor
int sock = *(int *) socket_desc;
char *message, client_message[3000];
puts("sending welcome msg to client...");
write(sock, message, 3000);
int reti;
//compile a regexp that checks for valid user input
regcomp(&regex, "([dg] [0-9]+)|([v] .+)|(p [0-9]+ .+)|q", REG_EXTENDED);
//Receive a message from client
char *input[3];
while(1){
//wait for some client input
recv(sock, client_message, 2000, 0);
//check the input with the regexp
reti = regexec(&regex, client_message, 0, NULL, REG_EXTENDED);
if (!reti) {
//tokenize the client input with \n as a delim char
char *token = strtok(client_message, " ");
int i = 0;
while (token) {
input[i] = token;
token = strtok(NULL, " ");
i++;
}
//quit operation
if (strcmp(input[0], "q") == 0) {
//if a client quits, the server dies. TODO: fix
puts("quitting");
//free(socket_desc);
close(socket_desc);
return 0;
}
//user input does not match regexp, try again..
} else if (reti == REG_NOMATCH) {
error_buffer = invalid_user_input;
check_err_buffer(sock);
usleep(100);
write(sock, " ", 2);
}
}
//Free the socket pointer
free(socket_desc);
return 0;
}
On the client side i test if message[0] == 'q' and I close the socket.
I would be very happy if i will get some help or hints to solve this problem. Thank you

Answer 1

As here
new_sock = malloc(1);
the code allocates 1 byte only, this following line
*new_sock = client_sock;
writes to invalid memory, as an int is assigned, and sizeof int bytes are written to where new_sock points. By definition sizeof int is at least 2, probably more, With this undefined behaviour is invoked. Anything may happen from then on.
To fix this do
new_sock = malloc(sizeof *new_sock);
instead.
Inspecting the return value of functions is debugging for free. close(socket_desc); is nonsense and definitely would return -1 and set errno to EBADFD.
Replace
close(socket_desc);
by
if (-1 == close(socket_desc))
{
perror("close() falied");
}
to see how the code as it stand fails.