linux/net/unix
Andrey Vagin ba94f3088b 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 <avagin@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
2017-02-02 21:58:02 -05:00
..
af_unix.c unix: add ioctl to open a unix socket file with O_PATH 2017-02-02 21:58:02 -05:00
diag.c unix_diag: fix incorrect sign extension in unix_lookup_by_ino 2016-02-19 23:49:23 -05:00
garbage.c unix: correctly track in-flight fds in sending process user_struct 2016-02-08 10:30:42 -05:00
Kconfig net: Default UDP and UNIX diag to 'n'. 2012-01-07 12:13:06 -08:00
Makefile unix_diag: Write it into kbuild 2011-12-16 13:48:29 -05:00
sysctl_net_unix.c net: Convert uses of typedef ctl_table to struct ctl_table 2013-06-13 02:36:09 -07:00