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SubjectRe: [PATCH] vfs: move_mount: reject moving kernel internal mounts
On Mon, Jul 01, 2019 at 07:22:39PM +0100, Al Viro wrote:

> FWIW, it's not just move_mount(2) - I'd expect
>
> int fds[2];
> char s[80];
>
> pipe(fds);
> sprintf(s, "/dev/fd/%d", fds[0]);
> mount(s, "/dev/null", NULL, MS_MOVE, 0);
>
> to step into exactly the same thing. mount(2) does follow symlinks -
> always had...

The same goes for e.g.

#define _GNU_SOURCE
#include <sched.h>
#include <sys/mount.h>
#include <stdio.h>
#include <sys/epoll.h>

main()
{
char s[80];
unshare(CLONE_NEWNS); // so nobody else gets confused
sprintf(s, "/dev/fd/%d", epoll_create1(0));
mount(s, "/dev/null", NULL, MS_MOVE, 0); // see if it oopses
}

modulo error-checking, etc.

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