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authorJamie Iles <jamie.iles@oracle.com>2017-01-11 03:57:54 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2017-01-11 05:31:55 +0300
commit2d39b3cd34e6d323720d4c61bd714f5ae202c022 (patch)
treebf9093d02ec3ff74731d0f16868e7e6ee82da42e
parent20f664aabeb88d582b623a625f83b0454fa34f07 (diff)
downloadlinux-2d39b3cd34e6d323720d4c61bd714f5ae202c022.tar.xz
signal: protect SIGNAL_UNKILLABLE from unintentional clearing.
Since commit 00cd5c37afd5 ("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@oracle.com Signed-off-by: Jamie Iles <jamie.iles@oracle.com> Acked-by: Oleg Nesterov <oleg@redhat.com> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Ingo Molnar <mingo@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--include/linux/sched.h10
-rw-r--r--kernel/signal.c4
2 files changed, 12 insertions, 2 deletions
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 4d1905245c7a..ad3ec9ec61f7 100644
--- a/include/linux/sched.h
+++ b/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 --git a/kernel/signal.c b/kernel/signal.c
index ff046b73ff2d..3603d93a1968 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -346,7 +346,7 @@ static bool task_participate_group_stop(struct task_struct *task)
* 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, struct task_struct *p, bool force)
* 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;
}