On Linux/MIPS, a simple test program can create unkillable process.
The "sigkill priority fix" was introduced in 2.6.12, but it does not
effective for signals sent by force_sig() in kernel. For detailed
behavior and testcase, please look at this thread in linux-mips ML:
http://www.linux-mips.org/cgi-bin/mesg.cgi?a=linux-mips&i=20050907.014234.108739386.anemo%40mba.ocn.ne.jp
Here is a proposal fix for generic signal handling code.
Patch comment:
The "sigkill priority fix" does not work as it desired if any signal
(< SIGKILL) was queued by force_sig() in kernel. Search SIGKILL in
tsk->pending and tsk->signal->shared_pending first, then search
another signals.
Signed-off-by: Atsushi Nemoto <[email protected]>
--- linux-2.6.13/kernel/signal.c 2005-08-29 08:41:01.000000000 +0900
+++ linux/kernel/signal.c 2005-09-07 01:33:52.338420760 +0900
@@ -520,19 +520,14 @@
}
static int __dequeue_signal(struct sigpending *pending, sigset_t *mask,
- siginfo_t *info)
+ siginfo_t *info, int sig)
{
- int sig = 0;
-
- /* SIGKILL must have priority, otherwise it is quite easy
- * to create an unkillable process, sending sig < SIGKILL
- * to self */
- if (unlikely(sigismember(&pending->signal, SIGKILL))) {
- if (!sigismember(mask, SIGKILL))
- sig = SIGKILL;
- }
-
- if (likely(!sig))
+ if (sig) {
+ /* check signal with priority first */
+ if (likely(!sigismember(&pending->signal, sig)) ||
+ sigismember(mask, sig))
+ sig = 0;
+ } else
sig = next_signal(pending, mask);
if (sig) {
if (current->notifier) {
@@ -561,10 +556,18 @@
*/
int dequeue_signal(struct task_struct *tsk, sigset_t *mask, siginfo_t *info)
{
- int signr = __dequeue_signal(&tsk->pending, mask, info);
+ /* SIGKILL must have priority, otherwise it is quite easy
+ * to create an unkillable process, sending sig < SIGKILL
+ * to self */
+ int signr = __dequeue_signal(&tsk->pending, mask, info, SIGKILL);
+ if (likely(!signr))
+ signr = __dequeue_signal(&tsk->signal->shared_pending,
+ mask, info, SIGKILL);
+ if (likely(!signr))
+ signr = __dequeue_signal(&tsk->pending, mask, info, 0);
if (!signr)
signr = __dequeue_signal(&tsk->signal->shared_pending,
- mask, info);
+ mask, info, 0);
if (signr && unlikely(sig_kernel_stop(signr))) {
/*
* Set a marker that we have dequeued a stop signal. Our
---
Atsushi Nemoto
-
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