Messages in this thread Patch in this message | | | Date | Thu, 22 Nov 2007 20:56:22 +0300 | From | Oleg Nesterov <> | Subject | [PATCH -mm 4/2] ptrace_stop: fix racy nonstop_code setting |
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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>
--- PT/kernel/signal.c~4_non_stop 2007-11-22 16:59:35.000000000 +0300 +++ PT/kernel/signal.c 2007-11-22 20:29:11.000000000 +0300 @@ -1601,10 +1601,10 @@ static inline int may_ptrace_stop(void) * That makes it a way to test a stopped process for * being ptrace-stopped vs being job-control-stopped. * - * If we actually decide not to stop at all because the tracer is gone, - * we leave nostop_code in current->exit_code. + * If we actually decide not to stop at all because the tracer + * is gone, we keep current->exit_code unless clear_code. */ -static void ptrace_stop(int exit_code, int nostop_code, siginfo_t *info) +static void ptrace_stop(int exit_code, int clear_code, siginfo_t *info) { /* * If there is a group stop in progress, @@ -1631,7 +1631,8 @@ static void ptrace_stop(int exit_code, i * Don't drop the lock yet, another tracer may come. */ __set_current_state(TASK_RUNNING); - current->exit_code = nostop_code; + if (clear_code) + current->exit_code = 0; read_unlock(&tasklist_lock); } @@ -1665,7 +1666,7 @@ void ptrace_notify(int exit_code) /* Let the debugger run. */ spin_lock_irq(¤t->sighand->siglock); - ptrace_stop(exit_code, 0, &info); + ptrace_stop(exit_code, 1, &info); spin_unlock_irq(¤t->sighand->siglock); } @@ -1813,7 +1814,7 @@ relock: ptrace_signal_deliver(regs, cookie); /* Let the debugger run. */ - ptrace_stop(signr, signr, info); + ptrace_stop(signr, 0, info); /* We're back. Did the debugger cancel the sig? */ signr = current->exit_code; - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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