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sched,signal,ptrace: Rework TASK_TRACED, TASK_STOPPED state

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Currently ptrace_stop() / do_signal_stop() rely on the special states
TASK_TRACED and TASK_STOPPED resp. to keep unique state. That is, this
state exists only in task->__state and nowhere else.

There's two spots of bother with this:

 - PREEMPT_RT has task->saved_state which complicates matters,
   meaning task_is_{traced,stopped}() needs to check an additional
   variable.

 - An alternative freezer implementation that itself relies on a
   special TASK state would loose TASK_TRACED/TASK_STOPPED and will
   result in misbehaviour.

As such, add additional state to task->jobctl to track this state
outside of task->__state.

NOTE: this doesn't actually fix anything yet, just adds extra state.

--EWB
  * didn't add a unnecessary newline in signal.h
  * Update t->jobctl in signal_wake_up and ptrace_signal_wake_up
    instead of in signal_wake_up_state.  This prevents the clearing
    of TASK_STOPPED and TASK_TRACED from getting lost.
  * Added warnings if JOBCTL_STOPPED or JOBCTL_TRACED are not cleared

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20220421150654.757693825@infradead.org
Tested-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Link: https://lkml.kernel.org/r/20220505182645.497868-12-ebiederm@xmission.com
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
This commit is contained in:
Peter Zijlstra
2022-05-03 15:57:47 -05:00
committed by Eric W. Biederman
parent 5b4197cb28
commit 31cae1eaae
5 changed files with 45 additions and 14 deletions
Download Patch File Download Diff File Expand all files Collapse all files

10
kernel/signal.c
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@@ -762,7 +762,10 @@ still_pending:
*/
void signal_wake_up_state(struct task_struct *t, unsigned int state)
{
lockdep_assert_held(&t->sighand->siglock);
set_tsk_thread_flag(t, TIF_SIGPENDING);
/*
* TASK_WAKEKILL also means wake it up in the stopped/traced/killable
* case. We don't check t->state here because there is a race with it
@@ -930,9 +933,10 @@ static bool prepare_signal(int sig, struct task_struct *p, bool force)
for_each_thread(p, t) {
flush_sigqueue_mask(&flush, &t->pending);
task_clear_jobctl_pending(t, JOBCTL_STOP_PENDING);
if (likely(!(t->ptrace & PT_SEIZED)))
if (likely(!(t->ptrace & PT_SEIZED))) {
t->jobctl &= ~JOBCTL_STOPPED;
wake_up_state(t, __TASK_STOPPED);
else
} else
ptrace_trap_notify(t);
}
@@ -2218,6 +2222,7 @@ static int ptrace_stop(int exit_code, int why, unsigned long message,
return exit_code;
set_special_state(TASK_TRACED);
current->jobctl |= JOBCTL_TRACED;
/*
* We're committing to trapping. TRACED should be visible before
@@ -2436,6 +2441,7 @@ static bool do_signal_stop(int signr)
if (task_participate_group_stop(current))
notify = CLD_STOPPED;
current->jobctl |= JOBCTL_STOPPED;
set_special_state(TASK_STOPPED);
spin_unlock_irq(&current->sighand->siglock);