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    SubjectRe: [PATCH] sys_getppid: add missing rcu_dereference
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    On Tue, Dec 6, 2011 at 6:45 PM, Mandeep Singh Baines <msb@chromium.org> wrote:
    > In order to safely dereference current->real_parent inside an
    > rcu_read_lock, we need an rcu_dereference.
    >
    > Signed-off-by: Mandeep Singh Baines <msb@chromium.org>
    > Cc: Thomas Gleixner <tglx@linutronix.de>
    > Cc: Pavel Emelyanov <xemul@openvz.org>
    > Cc: Oleg Nesterov <oleg@redhat.com>
    > Cc: Andrew Morton <akpm@linux-foundation.org>
    > Cc: Kees Cook <keescook@chromium.org>
    > ---
    >  kernel/timer.c |    2 +-
    >  1 files changed, 1 insertions(+), 1 deletions(-)
    >
    > diff --git a/kernel/timer.c b/kernel/timer.c
    > index dbaa624..9c3c62b 100644
    > --- a/kernel/timer.c
    > +++ b/kernel/timer.c
    > @@ -1368,7 +1368,7 @@ SYSCALL_DEFINE0(getppid)
    >        int pid;
    >
    >        rcu_read_lock();
    > -       pid = task_tgid_vnr(current->real_parent);
    > +       pid = task_tgid_vnr(rcu_dereference(current->real_parent));
    >        rcu_read_unlock();
    >
    >        return pid;

    Should parent and real_parent also be marked in sched.h with __rcu so
    sparse can find other missing rcu_dereference()s? And if not, why?
    (tasklist lock?)

    I think I see at least are few other users (security/apparmor/audit.c,
    security/tomoyo/common.h, kernel/sched.c) that need rcu_dereference()
    when accessing real_parent, there are probably more.

    -Kees

    --
    Kees Cook
    ChromeOS Security
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