pidns: disable pid allocation if pid_ns_prepare_proc() is failed in alloc_pid()

alloc_pidmap() advances pid_namespace::last_pid.  When first pid
allocation fails, then next created process will have pid 2 and
pid_ns_prepare_proc() won't be called.  So, pid_namespace::proc_mnt will
never be initialized (not to mention that there won't be a child
reaper).

I saw crash stack of such case on kernel 3.10:

    BUG: unable to handle kernel NULL pointer dereference at (null)
    IP: proc_flush_task+0x8f/0x1b0
    Call Trace:
        release_task+0x3f/0x490
        wait_consider_task.part.10+0x7ff/0xb00
        do_wait+0x11f/0x280
        SyS_wait4+0x7d/0x110

We may fix this by restore of last_pid in 0 or by prohibiting of futher
allocations.  Since there was a similar issue in Oleg Nesterov's commit
314a8ad0f18a ("pidns: fix free_pid() to handle the first fork failure").
and it was fixed via prohibiting allocation, let's follow this way, and
do the same.

Link: http://lkml.kernel.org/r/149201021004.4863.6762095011554287922.stgit@localhost.localdomain
Signed-off-by: Kirill Tkhai <[email protected]>
Acked-by: Cyrill Gorcunov <[email protected]>
Cc: Andrei Vagin <[email protected]>
Cc: Andreas Gruenbacher <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Michael Kerrisk <[email protected]>
Cc: Al Viro <[email protected]>
Cc: Oleg Nesterov <[email protected]>
Cc: Paul Moore <[email protected]>
Cc: Eric Biederman <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Serge Hallyn <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions