unix: add ioctl to open a unix socket file with O_PATH (ba94f308) · Commits · 戴 / test

This ioctl opens a file to which a socket is bound and returns a file descriptor. The caller has to have CAP_NET_ADMIN in the socket network namespace. Currently it is impossible to get a path and a mount point for a socket file. socket_diag reports address, device ID and inode number for unix sockets. An address can contain a relative path or a file may be moved somewhere. And these properties say nothing about a mount namespace and a mount point of a socket file. With the introduced ioctl, we can get a path by reading /proc/self/fd/X and get mnt_id from /proc/self/fdinfo/X. In CRIU we are going to use this ioctl to dump and restore unix socket. Here is an example how it can be used: $ strace -e socket,bind,ioctl ./test /tmp/test_sock socket(AF_UNIX, SOCK_STREAM, 0) = 3 bind(3, {sa_family=AF_UNIX, sun_path="test_sock"}, 11) = 0 ioctl(3, SIOCUNIXFILE, 0) = 4 ^Z $ ss -a | grep test_sock u_str LISTEN 0 1 test_sock 17798 * 0 $ ls -l /proc/760/fd/{3,4} lrwx------ 1 root root 64 Feb 1 09:41 3 -> 'socket:[17798]' l--------- 1 root root 64 Feb 1 09:41 4 -> /tmp/test_sock $ cat /proc/760/fdinfo/4 pos: 0 flags: 012000000 mnt_id: 40 $ cat /proc/self/mountinfo | grep "^40\s" 40 19 0:37 / /tmp rw shared:23 - tmpfs tmpfs rw Signed-off-by:

Andrei Vagin <avagin@openvz.org> Signed-off-by:

David S. Miller <davem@davemloft.net>

include/uapi/linux/un.h

+2 −0

Original line number	Diff line number	Diff line
		@@ -10,4 +10,6 @@ struct sockaddr_un {
		char sun_path[UNIX_PATH_MAX]; /* pathname */
		};

		#define SIOCUNIXFILE (SIOCPROTOPRIVATE + 0) /* open a socket file with O_PATH */

		#endif /* _LINUX_UN_H */

net/unix/af_unix.c

+41 −0

Original line number	Diff line number	Diff line
		@@ -117,6 +117,7 @@
		#include <net/checksum.h>
		#include <linux/security.h>
		#include <linux/freezer.h>
		#include <linux/file.h>

		struct hlist_head unix_socket_table[2 * UNIX_HASH_SIZE];
		EXPORT_SYMBOL_GPL(unix_socket_table);
		@@ -2592,6 +2593,43 @@ long unix_outq_len(struct sock *sk)
		}
		EXPORT_SYMBOL_GPL(unix_outq_len);

		static int unix_open_file(struct sock *sk)
		{
		struct path path;
		struct file *f;
		int fd;

		if (!ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN))
		return -EPERM;

		unix_state_lock(sk);
		path = unix_sk(sk)->path;
		if (!path.dentry) {
		unix_state_unlock(sk);
		return -ENOENT;
		}

		path_get(&path);
		unix_state_unlock(sk);

		fd = get_unused_fd_flags(O_CLOEXEC);
		if (fd < 0)
		goto out;

		f = dentry_open(&path, O_PATH, current_cred());
		if (IS_ERR(f)) {
		put_unused_fd(fd);
		fd = PTR_ERR(f);
		goto out;
		}

		fd_install(fd, f);
		out:
		path_put(&path);

		return fd;
		}

		static int unix_ioctl(struct socket *sock, unsigned int cmd, unsigned long arg)
		{
		struct sock *sk = sock->sk;
		@@ -2610,6 +2648,9 @@ static int unix_ioctl(struct socket *sock, unsigned int cmd, unsigned long arg)
		else
		err = put_user(amount, (int __user *)arg);
		break;
		case SIOCUNIXFILE:
		err = unix_open_file(sk);
		break;
		default:
		err = -ENOIOCTLCMD;
		break;

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