ptrace_stop: fix racy nonstop_code setting
If the tracer is gone and we are not going to stop, ptrace_stop() sets ->exit_code = nostop_code. However, the tracer could actually clear the exit code before detaching. In that case get_signal_to_deliver() "resends" the signal which was cancelled by the debugger. For example, it is possible that a quick PTRACE_ATTACH + PTRACE_DETACH can leave the tracee in STOPPED state. Change the behaviour of ptrace_stop(). If the caller is ptrace notify(), we should always clear ->exit_code. If the caller is get_signal_to_deliver(), we should not touch it at all. To do so, change the nonstop_code parameter to "bool clear_code" and change the callers accordingly. Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Acked-by: Roland McGrath <roland@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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9cbab81005
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1 changed files with 7 additions and 6 deletions
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@ -1591,10 +1591,10 @@ static int sigkill_pending(struct task_struct *tsk)
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* That makes it a way to test a stopped process for
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* That makes it a way to test a stopped process for
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* being ptrace-stopped vs being job-control-stopped.
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* being ptrace-stopped vs being job-control-stopped.
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*
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*
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* If we actually decide not to stop at all because the tracer is gone,
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* If we actually decide not to stop at all because the tracer
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* we leave nostop_code in current->exit_code.
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* is gone, we keep current->exit_code unless clear_code.
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*/
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*/
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static void ptrace_stop(int exit_code, int nostop_code, siginfo_t *info)
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static void ptrace_stop(int exit_code, int clear_code, siginfo_t *info)
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{
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{
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int killed = 0;
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int killed = 0;
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@ -1641,7 +1641,8 @@ static void ptrace_stop(int exit_code, int nostop_code, siginfo_t *info)
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* Don't drop the lock yet, another tracer may come.
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* Don't drop the lock yet, another tracer may come.
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*/
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*/
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__set_current_state(TASK_RUNNING);
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__set_current_state(TASK_RUNNING);
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current->exit_code = nostop_code;
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if (clear_code)
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current->exit_code = 0;
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read_unlock(&tasklist_lock);
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read_unlock(&tasklist_lock);
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}
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}
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@ -1675,7 +1676,7 @@ void ptrace_notify(int exit_code)
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/* Let the debugger run. */
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/* Let the debugger run. */
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spin_lock_irq(¤t->sighand->siglock);
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spin_lock_irq(¤t->sighand->siglock);
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ptrace_stop(exit_code, 0, &info);
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ptrace_stop(exit_code, 1, &info);
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spin_unlock_irq(¤t->sighand->siglock);
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spin_unlock_irq(¤t->sighand->siglock);
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}
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}
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@ -1782,7 +1783,7 @@ int get_signal_to_deliver(siginfo_t *info, struct k_sigaction *return_ka,
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ptrace_signal_deliver(regs, cookie);
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ptrace_signal_deliver(regs, cookie);
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/* Let the debugger run. */
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/* Let the debugger run. */
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ptrace_stop(signr, signr, info);
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ptrace_stop(signr, 0, info);
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/* We're back. Did the debugger cancel the sig? */
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/* We're back. Did the debugger cancel the sig? */
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signr = current->exit_code;
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signr = current->exit_code;
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