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unix: add ioctl to open a unix socket file with O_PATH

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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>
This commit is contained in:
Andrey Vagin 2017-02-01 11:00:45 -08:00 committed by David S. Miller
parent 2a7b621669
commit ba94f3088b
2 changed files with 43 additions and 0 deletions
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2
include/uapi/linux/un.h
View File

@ -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 */

41
net/unix/af_unix.c
View File

@ -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;