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    Subject[PATCH 2/6][v5] Protect init from unwanted signals more

    From: Oleg Nesterov <oleg@redhat.com>
    Date: Wed, 24 Dec 2008 13:35:23 -0800
    Subject: [PATCH 2/6][v5] Protect init from unwanted signals more

    (This is a modified version of the patch submitted by Oleg Nesterov
    http://lkml.org/lkml/2008/11/18/249 and tries to address comments
    that came up in that discussion)

    init ignores the SIG_DFL signals but we queue them anyway, including
    SIGKILL. This is mostly OK, the signal will be dropped silently when
    dequeued, but the pending SIGKILL has 2 bad implications:

    - it implies fatal_signal_pending(), so we confuse things
    like wait_for_completion_killable/lock_page_killable.

    - for the sub-namespace inits, the pending SIGKILL can
    mask (legacy_queue) the subsequent SIGKILL from the
    parent namespace which must kill cinit reliably.
    (preparation, cinits don't have SIGNAL_UNKILLABLE yet)

    The patch can't help when init is ptraced, but ptracing of init is
    not "safe" anyway.

    Changelog[v5]:
    - (Oleg Nesterov) Remove SIG_IGN check in sig_task_ignored()
    and let sig_handler_ignored() check SIG_IGN.

    Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
    Acked-by: Roland McGrath <roland@redhat.com>
    ---
    kernel/signal.c | 16 +++++++++++++---
    1 files changed, 13 insertions(+), 3 deletions(-)

    diff --git a/kernel/signal.c b/kernel/signal.c
    index 7945e71..30b9c5c 100644
    --- a/kernel/signal.c
    +++ b/kernel/signal.c
    @@ -53,10 +53,21 @@ static int sig_handler_ignored(void __user *handler, int sig)
    (handler == SIG_DFL && sig_kernel_ignore(sig));
    }

    -static int sig_ignored(struct task_struct *t, int sig)
    +static int sig_task_ignored(struct task_struct *t, int sig)
    {
    void __user *handler;

    + handler = sig_handler(t, sig);
    +
    + if (unlikely(t->signal->flags & SIGNAL_UNKILLABLE) &&
    + handler == SIG_DFL)
    + return 1;
    +
    + return sig_handler_ignored(handler, sig);
    +}
    +
    +static int sig_ignored(struct task_struct *t, int sig)
    +{
    /*
    * Blocked signals are never ignored, since the
    * signal handler may change by the time it is
    @@ -65,8 +76,7 @@ static int sig_ignored(struct task_struct *t, int sig)
    if (sigismember(&t->blocked, sig) || sigismember(&t->real_blocked, sig))
    return 0;

    - handler = sig_handler(t, sig);
    - if (!sig_handler_ignored(handler, sig))
    + if (!sig_task_ignored(t, sig))
    return 0;

    /*
    --
    1.5.2.5


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