From: Sukadev Bhattiprolu <[email protected]> Date: Sat, 20 Dec 2008 14:15:41 -0800 Subject: [RFC][PATCH 6/6][v3] Protect cinit from blocked fatal signals
Normally SIG_DFL signals to global and container-init are dropped early. But if a signal is blocked when it is posted, we cannot drop the signal since the receiver may install a handler before unblocking the signal. Once this signal is queued however, the receiver container-init has no way of knowing if the signal was sent from an ancestor or descendant namespace. This patch ensures that contianer-init drop all SIG_DFL signals in get_signal_to_deliver() except SIGKILL/SIGSTOP. If SIGSTOP/SIGKILL originate from a descendant of container-init they are never queued (i.e dropped in sig_ignored() in an earler patch). If SIGSTOP/SIGKILL originate from parent namespace, the signal is queued and container-init processes the signal. See comments in patch below for details. Signed-off-by: Sukadev Bhattiprolu <[email protected]> --- kernel/signal.c | 41 +++++++++++++++++++++++++++++++++++++++-- 1 files changed, 39 insertions(+), 2 deletions(-) diff --git a/kernel/signal.c b/kernel/signal.c index 2dfca62..4abacf4 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -1816,6 +1816,42 @@ static int ptrace_signal(int signr, siginfo_t *info, return signr; } +/* + * Return 1 if the signal @sig should NOT kill the task that owns @signal. + * Return 0 otherwise. + * + * If @signal refers to the global-init, it is unkillable (return 1). + * + * If @signal refers to a task a that is neither a container-init nor the + * global init, the task is killable (return 0). + * + * If @signal refers to a container-init and @sig is either SIGKILL or + * SIGSTOP, the signal must be from an ancestor container. So the task + * (container-init) should be killable (return 0). + * + * If @signal refers to a container-init and @sig is neither SIGKILL nor + * SIGSTOP, it was queued because it was blocked when it was posed. The + * signal may have come from same container - hence it should not be + * killable (return 1). + * + * Note: + * This means that SIGKILL is the only sure way to terminate a + * container-init even from ancestor namespace. + */ +static int sig_unkillable(struct signal_struct *signal, int sig) +{ + if (signal->flags & SIGNAL_UNKILLABLE_FROM_NS) + return !sig_kernel_only(sig); + + /* + * We must have dropped SIGKILL/SIGSTOP in sig_ignored() + * TODO: Remove BUG_ON(). + */ + BUG_ON(signal->flags & SIGNAL_UNKILLABLE && sig_kernel_only(sig)); + + return (signal->flags & SIGNAL_UNKILLABLE); +} + int get_signal_to_deliver(siginfo_t *info, struct k_sigaction *return_ka, struct pt_regs *regs, void *cookie) { @@ -1907,9 +1943,10 @@ relock: /* * Global init gets no signals it doesn't want. + * Container-init gets no signals it doesn't want from same + * container. */ - if (unlikely(signal->flags & SIGNAL_UNKILLABLE) && - !signal_group_exit(signal)) + if (sig_unkillable(signal, signr) && !signal_group_exit(signal)) continue; if (sig_kernel_stop(signr)) { -- 1.5.2.5 _______________________________________________ Containers mailing list [email protected] https://lists.linux-foundation.org/mailman/listinfo/containers _______________________________________________ Devel mailing list [email protected] https://openvz.org/mailman/listinfo/devel
