signal: protect SIGNAL_UNKILLABLE from unintentional clearing. (2d39b3cd) · Commits · 戴 / test

Since commit ("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>

include/linux/sched.h

+10 −0

Original line number	Diff line number	Diff line
		@@ -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)
		{

kernel/signal.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -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;
		}

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