How to create Unix Domain Socket with a specific permissions in C?

Question

I have a simple code, like:

sockaddr_un address;
address.sun_family = AF_UNIX;
strcpy(address.sun_path, path);
unlink(path);

int fd = socket(AF_UNIX, SOCK_STREAM, 0);
bind(fd, (sockaddr*)(&address), sizeof(address));
listen(fd, 100);

I want to atomically create the Unix Domain Socket file with a specific permissions, say: 0777. The manual doesn't say anything about socket file permissions with regard to umask or whatever. Even, if the umask does affect the socket file, then it's not an atomic way - in multi-threaded program.

I hope, there is a way to achieve my goal without using synchronization of umask() calls.

Answer 1

Another solution is to create a directory with the desired permissions, and then create the socket inside it (example code without any regard for error checking and buffer overflows):

// Create a directory with the proper permissions
mkdir(path, 0700);
// Append the name of the socket
strcat(path, "/socket_name");

// Create the socket normally
sockaddr_un address;
address.sun_family = AF_UNIX;
strcpy(address.sun_path, path);
int fd = socket(AF_UNIX, SOCK_STREAM, 0);
bind(fd, (sockaddr*)(&address), sizeof(address));
listen(fd, 100);