socket

Version

• Linux v5.8.13

Abstract

long sys_socket(int family, int type, int protocol);

Arguments

Return

Definition

sys_socket()

• file: net/socket.c

SYSCALL_DEFINE3(socket, int, family, int, type, int, protocol)
{
	return __sys_socket(family, type, protocol);
}

__sys_socket()

int __sys_socket(int family, int type, int protocol)
{
	int retval;
	struct socket *sock;
	int flags;

	/* Check the SOCK_* constants for consistency.  */
	BUILD_BUG_ON(SOCK_CLOEXEC != O_CLOEXEC);
	BUILD_BUG_ON((SOCK_MAX | SOCK_TYPE_MASK) != SOCK_TYPE_MASK);
	BUILD_BUG_ON(SOCK_CLOEXEC & SOCK_TYPE_MASK);
	BUILD_BUG_ON(SOCK_NONBLOCK & SOCK_TYPE_MASK);

	flags = type & ~SOCK_TYPE_MASK;
	if (flags & ~(SOCK_CLOEXEC | SOCK_NONBLOCK))
		return -EINVAL;
	type &= SOCK_TYPE_MASK;

	if (SOCK_NONBLOCK != O_NONBLOCK && (flags & SOCK_NONBLOCK))
		flags = (flags & ~SOCK_NONBLOCK) | O_NONBLOCK;

	retval = sock_create(family, type, protocol, &sock);
	if (retval < 0)
		return retval;

	return sock_map_fd(sock, flags & (O_CLOEXEC | O_NONBLOCK));
}

sock_create()

int sock_create(int family, int type, int protocol, struct socket **res)
{
	return __sock_create(current->nsproxy->net_ns, family, type, protocol, res, 0);
}
EXPORT_SYMBOL(sock_create);

__sock_create()

/**
 *	__sock_create - creates a socket
 *	@net: net namespace
 *	@family: protocol family (AF_INET, ...)
 *	@type: communication type (SOCK_STREAM, ...)
 *	@protocol: protocol (0, ...)
 *	@res: new socket
 *	@kern: boolean for kernel space sockets
 *
 *	Creates a new socket and assigns it to @res, passing through LSM.
 *	Returns 0 or an error. On failure @res is set to %NULL. @kern must
 *	be set to true if the socket resides in kernel space.
 *	This function internally uses GFP_KERNEL.
 */

int __sock_create(struct net *net, int family, int type, int protocol,
			 struct socket **res, int kern)
{
	int err;
	struct socket *sock;
	const struct net_proto_family *pf;

	/*
	 *      Check protocol is in range
	 */
	if (family < 0 || family >= NPROTO)
		return -EAFNOSUPPORT;
	if (type < 0 || type >= SOCK_MAX)
		return -EINVAL;

	/* Compatibility.

	   This uglymoron is moved from INET layer to here to avoid
	   deadlock in module load.
	 */
	if (family == PF_INET && type == SOCK_PACKET) {
		pr_info_once("%s uses obsolete (PF_INET,SOCK_PACKET)\n",
			     current->comm);
		family = PF_PACKET;
	}

	err = security_socket_create(family, type, protocol, kern);
	if (err)
		return err;

	/*
	 *	Allocate the socket and allow the family to set things up. if
	 *	the protocol is 0, the family is instructed to select an appropriate
	 *	default.
	 */
	sock = sock_alloc();
	if (!sock) {
		net_warn_ratelimited("socket: no more sockets\n");
		return -ENFILE;	/* Not exactly a match, but its the
				   closest posix thing */
	}

	sock->type = type;

#ifdef CONFIG_MODULES
	/* Attempt to load a protocol module if the find failed.
	 *
	 * 12/09/1996 Marcin: But! this makes REALLY only sense, if the user
	 * requested real, full-featured networking support upon configuration.
	 * Otherwise module support will break!
	 */
	if (rcu_access_pointer(net_families[family]) == NULL)
		request_module("net-pf-%d", family);
#endif

	rcu_read_lock();
	pf = rcu_dereference(net_families[family]);
	err = -EAFNOSUPPORT;
	if (!pf)
		goto out_release;

	/*
	 * We will call the ->create function, that possibly is in a loadable
	 * module, so we have to bump that loadable module refcnt first.
	 */
	if (!try_module_get(pf->owner))
		goto out_release;

	/* Now protected by module ref count */
	rcu_read_unlock();

	err = pf->create(net, sock, protocol, kern);
	if (err < 0)
		goto out_module_put;

	/*
	 * Now to bump the refcnt of the [loadable] module that owns this
	 * socket at sock_release time we decrement its refcnt.
	 */
	if (!try_module_get(sock->ops->owner))
		goto out_module_busy;

	/*
	 * Now that we're done with the ->create function, the [loadable]
	 * module can have its refcnt decremented
	 */
	module_put(pf->owner);
	err = security_socket_post_create(sock, family, type, protocol, kern);
	if (err)
		goto out_sock_release;
	*res = sock;

	return 0;

out_module_busy:
	err = -EAFNOSUPPORT;
out_module_put:
	sock->ops = NULL;
	module_put(pf->owner);
out_sock_release:
	sock_release(sock);
	return err;

out_release:
	rcu_read_unlock();
	goto out_sock_release;
}
EXPORT_SYMBOL(__sock_create);

sock_map_fd()

static int sock_map_fd(struct socket *sock, int flags)
{
	struct file *newfile;
	int fd = get_unused_fd_flags(flags);
	if (unlikely(fd < 0)) {
		sock_release(sock);
		return fd;
	}

	newfile = sock_alloc_file(sock, flags, NULL);
	if (!IS_ERR(newfile)) {
		fd_install(fd, newfile);
		return fd;
	}

	put_unused_fd(fd);
	return PTR_ERR(newfile);
}

sock_alloc_file()

/**
 *	sock_alloc_file - Bind a &socket to a &file
 *	@sock: socket
 *	@flags: file status flags
 *	@dname: protocol name
 *
 *	Returns the &file bound with @sock, implicitly storing it
 *	in sock->file. If dname is %NULL, sets to "".
 *	On failure the return is a ERR pointer (see linux/err.h).
 *	This function uses GFP_KERNEL internally.
 */

struct file *sock_alloc_file(struct socket *sock, int flags, const char *dname)
{
	struct file *file;

	if (!dname)
		dname = sock->sk ? sock->sk->sk_prot_creator->name : "";

	file = alloc_file_pseudo(SOCK_INODE(sock), sock_mnt, dname,
				O_RDWR | (flags & O_NONBLOCK),
				&socket_file_ops);
	if (IS_ERR(file)) {
		sock_release(sock);
		return file;
	}

	sock->file = file;
	file->private_data = sock;
	stream_open(SOCK_INODE(sock), file);
	return file;
}
EXPORT_SYMBOL(sock_alloc_file);