The patch titled
Subject: signal: protect SIGNAL_UNKILLABLE from unintentional clearing.
has been added to the -mm tree. Its filename is
signal-protect-signal_unkillable-from-unintentional-clearing.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/signal-protect-signal_unkillable-from-unintentional-clearing.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/signal-protect-signal_unkillable-from-unintentional-clearing.patch
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------------------------------------------------------
From: Jamie Iles <jamie.iles@xxxxxxxxxx>
Subject: signal: protect SIGNAL_UNKILLABLE from unintentional clearing.
Since 00cd5c37af (ptrace: permit ptracing of /sbin/init) we can now trace
init processes. init is initially protected with SIGNAL_UNKILLABLE which
will prevent fatal signals such as SIGSTOP, but there are a number of
paths during tracing where SIGNAL_UNKILLABLE can be implicitly cleared.
This can result in init becoming stoppable/killable after tracing. For
example, running:
while true; do kill -STOP 1; done &
strace -p 1
and then stopping strace and the kill loop will result in init being left
in state TASK_STOPPED. Sending SIGCONT to init will resume it, but init
will now respond to future SIGSTOP signals rather than ignoring them.
Make sure that when setting SIGNAL_STOP_CONTINUED/SIGNAL_STOP_STOPPED
that we don't clear SIGNAL_UNKILLABLE.
Link: http://lkml.kernel.org/r/20170104122017.25047-1-jamie.iles@xxxxxxxxxx
Signed-off-by: Jamie Iles <jamie.iles@xxxxxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/sched.h | 10 ++++++++++
kernel/signal.c | 4 ++--
2 files changed, 12 insertions(+), 2 deletions(-)
diff -puN include/linux/sched.h~signal-protect-signal_unkillable-from-unintentional-clearing include/linux/sched.h
--- a/include/linux/sched.h~signal-protect-signal_unkillable-from-unintentional-clearing
+++ a/include/linux/sched.h
@@ -854,6 +854,16 @@ struct signal_struct {
#define SIGNAL_UNKILLABLE 0x00000040 /* for init: ignore fatal signals */
+#define SIGNAL_STOP_MASK (SIGNAL_CLD_MASK | SIGNAL_STOP_STOPPED | \
+ SIGNAL_STOP_CONTINUED)
+
+static inline void signal_set_stop_flags(struct signal_struct *sig,
+ unsigned int flags)
+{
+ WARN_ON(sig->flags & (SIGNAL_GROUP_EXIT|SIGNAL_GROUP_COREDUMP));
+ sig->flags = (sig->flags & ~SIGNAL_STOP_MASK) | flags;
+}
+
/* If true, all threads except ->group_exit_task have pending SIGKILL */
static inline int signal_group_exit(const struct signal_struct *sig)
{
diff -puN kernel/signal.c~signal-protect-signal_unkillable-from-unintentional-clearing kernel/signal.c
--- a/kernel/signal.c~signal-protect-signal_unkillable-from-unintentional-clearing
+++ a/kernel/signal.c
@@ -346,7 +346,7 @@ static bool task_participate_group_stop(
* fresh group stop. Read comment in do_signal_stop() for details.
*/
if (!sig->group_stop_count && !(sig->flags & SIGNAL_STOP_STOPPED)) {
- sig->flags = SIGNAL_STOP_STOPPED;
+ signal_set_stop_flags(sig, SIGNAL_STOP_STOPPED);
return true;
}
return false;
@@ -843,7 +843,7 @@ static bool prepare_signal(int sig, stru
* will take ->siglock, notice SIGNAL_CLD_MASK, and
* notify its parent. See get_signal_to_deliver().
*/
- signal->flags = why | SIGNAL_STOP_CONTINUED;
+ signal_set_stop_flags(signal, why | SIGNAL_STOP_CONTINUED);
signal->group_stop_count = 0;
signal->group_exit_code = 0;
}
_
Patches currently in -mm which might be from jamie.iles@xxxxxxxxxx are
signal-protect-signal_unkillable-from-unintentional-clearing.patch
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