Bug#841935: pbuilder: incorrect permissions on /dev/ptmx breaks openpty()

[Yuriy M. Kaminskiy]

Andreas Henriksson <andreas at fatal.se> writes:

> It seems /dev/ptmx has incorrect permissions in a pbuilder chroot:
>
> # ls -l /dev/ptmx
> lrwxrwxrwx 1 root root 8 Oct  4 06:43 /dev/ptmx -> pts/ptmx
> # ls -l /dev/pts/ptmx
> c--------- 1 root root 5, 2 Oct 24 14:46 /dev/pts/ptmx
>
> Please compare to what's stated in
> https://www.kernel.org/doc/Documentation/filesystems/devpts.txt
>
> For comparison this is from my regular system:
> $ ls -l /dev/ptmx /dev/pts/ptmx
> crw-rw-rw- 1 root tty  5, 2 okt 24 17:03 /dev/ptmx
> c--------- 1 root root 5, 2 okt 11 12:35 /dev/pts/ptmx
>
> I've hacked up my pbuilder installation and confirmed that appending
> ",ptmxmode=0666" to the /dev/pts mount flags fixes the issue.

IIRC, it would also need `,newinstance` option by then (otherwise
it will clobber "host system" devpts options).

> This issue was detected while building the util-linux package where
> the testsuite now has started to fail (specifically the
> tests/ts/script/buffering-race test, since 'script' uses openpty).
>
> See attached patch.