On Tue, Oct 07, 2014 at 02:24:36PM +0100, Al Viro wrote:
> On Tue, Oct 07, 2014 at 04:00:12PM +0400, Andrey Vagin wrote:
> > This patch fixes a bug, which is triggered by following code:
> > while (1) {
> > if (umount2("/", MNT_DETACH) ||
> > setns(fd, CLONE_NEWNS))
> > return break;
> > }
>
> Excuse me, but that makes no sense whatsoever (not to mention that
> reproducer won't compile - return break; alone is enough to make
> sure of that).
>
> Could you post the real reproducer?
#define _GNU_SOURCE
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sched.h>
#include <unistd.h>
#include <sys/mount.h>
int main(int argc, char **argv)
{
int fd;
fd = open("/proc/self/ns/mnt", O_RDONLY);
if (fd < 0)
return 1;
while (1) {
if (umount2("/", MNT_DETACH) ||
setns(fd, CLONE_NEWNS))
break;
}
return 0;
}
root@ubuntu:/home/avagin# gcc -Wall nsenter.c -o nsenter
root@ubuntu:/home/avagin# strace ./nsenter
execve("./nsenter", ["./nsenter"], [/* 22 vars */]) = 0
...
open("/proc/self/ns/mnt", O_RDONLY) = 3
umount("/", MNT_DETACH) = 0
setns(3, 131072) = 0
umount("/", MNT_DETACH
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