From ba94f3088b792b16ea576a256a6030feddc87f24 Mon Sep 17 00:00:00 2001 From: Andrey Vagin Date: Wed, 1 Feb 2017 11:00:45 -0800 Subject: [PATCH] unix: add ioctl to open a unix socket file with O_PATH 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 Signed-off-by: David S. Miller --- include/uapi/linux/un.h | 2 ++ net/unix/af_unix.c | 41 +++++++++++++++++++++++++++++++++++++++++ 2 files changed, 43 insertions(+) diff --git a/include/uapi/linux/un.h b/include/uapi/linux/un.h index 3ed3e46c1b1f..4f0ab3a548ad 100644 --- a/include/uapi/linux/un.h +++ b/include/uapi/linux/un.h @@ -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 */ diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c index cef79873b09d..e2d18b9f910f 100644 --- a/net/unix/af_unix.c +++ b/net/unix/af_unix.c @@ -117,6 +117,7 @@ #include #include #include +#include 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; -- 2.20.1