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    Subject[patch 01/39] pid: implement ns_of_pid
    2.6.28-stable review patch.  If anyone has any objections, please let us know.

    ------------------
    From: Eric W. Biederman <ebiederm@xmission.com>

    commit f9fb860f67b9542cd78d1558dec7058092b57d8e upstream.

    A current problem with the pid namespace is that it is easy to do pid
    related work after exit_task_namespaces which drops the nsproxy pointer.

    However if we are doing pid namespace related work we are always operating
    on some struct pid which retains the pid_namespace pointer of the pid
    namespace it was allocated in.

    So provide ns_of_pid which allows us to find the pid namespace a pid was
    allocated in.

    Using this we have the needed infrastructure to do pid namespace related
    work at anytime we have a struct pid, removing the chance of accidentally
    having a NULL pointer dereference when accessing current->nsproxy.

    Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
    Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
    Cc: Oleg Nesterov <oleg@redhat.com>
    Cc: Roland McGrath <roland@redhat.com>
    Cc: Bastian Blank <bastian@waldi.eu.org>
    Cc: Pavel Emelyanov <xemul@openvz.org>
    Cc: Nadia Derbey <Nadia.Derbey@bull.net>
    Acked-by: Serge Hallyn <serue@us.ibm.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

    ---
    include/linux/pid.h | 18 ++++++++++++++++++
    1 file changed, 18 insertions(+)
    --- a/include/linux/pid.h
    +++ b/include/linux/pid.h
    @@ -123,6 +123,24 @@ extern struct pid *alloc_pid(struct pid_
    extern void free_pid(struct pid *pid);

    /*
    + * ns_of_pid() returns the pid namespace in which the specified pid was
    + * allocated.
    + *
    + * NOTE:
    + * ns_of_pid() is expected to be called for a process (task) that has
    + * an attached 'struct pid' (see attach_pid(), detach_pid()) i.e @pid
    + * is expected to be non-NULL. If @pid is NULL, caller should handle
    + * the resulting NULL pid-ns.
    + */
    +static inline struct pid_namespace *ns_of_pid(struct pid *pid)
    +{
    + struct pid_namespace *ns = NULL;
    + if (pid)
    + ns = pid->numbers[pid->level].ns;
    + return ns;
    +}
    +
    +/*
    * the helpers to get the pid's id seen from different namespaces
    *
    * pid_nr() : global id, i.e. the id seen from the init namespace;


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