devpts: Make ptmx be owned by the userns owner as a fallback
New devpts instances have ptmx owned by the inner uid and gid 0.
For container-style namespaces (LXC, etc), this should have no
effect, this is fine.
For sandbox-style namespaces (xdg-app and similar), this is
problematic -- there may not be an inner 0:0. If that happens,
devpts mounts will fail.
Fix it by adding a fallback: if 0:0 is not mapped but the userns
owner and group are mapped, then ptmx will be owned by the namespace
owner.
This won't change behavior except in cases where mount would
currently return -EINVAL.
Cc: Alexander Larsson <alexl@redhat.com>
Cc: mclasen@redhat.com
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Linux Containers <containers@lists.linux-foundation.org>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
1 file changed
