Segmentation fault occurs when I'm accessing a struct's member - c

Question

A segmentation fault occurs when I want to access or modify the value of a struct member in C programming language.
I actually write a battleship networked game in C language (it is a student project). I have a structure named Player:
enum state{PLAYING = 0, WINNER = 1, LOOSER = 2};
enum action{ATTACK = 1, WAIT = 0, NOTHING = -1};
typedef struct Player Player;
struct Player
{
enum action action;
enum state state;
char name[25];
int isFirstPlayer;
Client* client;
Server* server;
Boards* boards;
};
the main function.
int main(int argc, char *argv[])
{
if(argc < 2)
{
errorUsage();
}
// Initialise player
Player player = newPlayer();
// I removed the network initialization here.
// play game
play_game(&player);
}
the segmentation fault occurs in the function play_game(Player* p):
void attack(Player* p)
{
char msg[2];
bzero(msg, strlen(msg));
printf("Where do you want to fire?");
scanf("%s", msg);
while(verifyEntryAttack(msg) != 1)
{
printf("ERROR Entry:\nFormat = A4, C9, ...\nColumns = A B C D E F G H I J\nRows = 0 1 2 3 4 5 6 7 8 9\n");
printf("please try again: ");
scanf("%s", msg);
}
sendData(p, msg);
Box my_attack_box;
my_attack_box.abs = msg[0];
my_attack_box.ord = msg[1]-'0';
updateMarkBoard(p, my_attack_box);
}
void receiveAttack(Player* p)
{
char received_attack[2];
receiveData(p, received_attack);
printf("I have received the attack: %s\n", received_attack);
Box my_attack_box;
my_attack_box.abs = received_attack[0];
my_attack_box.ord = received_attack[1]-'0';
endureAttack(my_attack_box, p);
}
void play_game(Player* p)
{
while(p->state == PLAYING){
printPlayer(p); //print the game boards.
if(p->action == ATTACK){
printf("Your turn to attack.\n");
attack(p); //attack the ennemy
printf("end of attack turn.\n");
} else if(p->action == WAIT){
printf("wait for an attack...\n");
receiveAttack(p); //receive the attack from the ennemy.
printf("end of waiting turn.\n");
}
if(p->action == WAIT){
p->action = ATTACK;
}
else{
p->action = WAIT;
}
}
}
After one turn in the while loop, the program says "segmentation fault". My tests show that is the p->action which is the problem.
See below the program output that shows the problem: outputs screenshot.
The entire code is available here: GitLab repo link.
It's like my program can't access the action member of my player.
Does anyone have any ideas?

Answer 1

char msg[2];
bzero(msg, strlen(msg));
Okay, so here you try to calculate the length of an uninitialized string, a typical source of page faults (and kernel vulnerabilities). strlen does not know your array's size, it simply looks for a zero character and is likely to get out of your page very soon. Even if the program does not crash at this point, bzero will do the trick as it is likely to write memory out of your reach.
Note that a cell is usually described with at least two characters ("C4" or so), so scanf will write the terminating zero character past the end of msg (again, this could be even out of your available memory). Increase msg's size so that it can accommodate at least valid inputs (at least three chars, the more the better). And you don't need to call strlen here; if you want to pre-clear your array, the simplest way would be to initialize it properly: char msg[256] = {'\0'};.
Next, you haven't shown your NewPlayer()'s code, but your struct contains three pointer fields, please double-check they are allocated, and initialized, properly.