Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754799AbaBEUGH (ORCPT ); Wed, 5 Feb 2014 15:06:07 -0500 Received: from mail.windriver.com ([147.11.1.11]:54791 "EHLO mail.windriver.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752507AbaBEUFk (ORCPT ); Wed, 5 Feb 2014 15:05:40 -0500 From: Paul Gortmaker To: , CC: Oleg Nesterov , Paul Gortmaker Subject: [v2.6.34-stable 087/213] ptrace: ptrace_resume() shouldn't wake up !TASK_TRACED thread Date: Wed, 5 Feb 2014 15:00:42 -0500 Message-ID: <1391630568-49251-88-git-send-email-paul.gortmaker@windriver.com> X-Mailer: git-send-email 1.8.5.2 In-Reply-To: <1391630568-49251-1-git-send-email-paul.gortmaker@windriver.com> References: <1391630568-49251-1-git-send-email-paul.gortmaker@windriver.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Oleg Nesterov ------------------- This is a commit scheduled for the next v2.6.34 longterm release. http://git.kernel.org/?p=linux/kernel/git/paulg/longterm-queue-2.6.34.git If you see a problem with using this for longterm, please comment. ------------------- commit 0666fb51b1483f27506e212cc7f7b2645b5c7acc upstream. It is not clear why ptrace_resume() does wake_up_process(). Unless the caller is PTRACE_KILL the tracee should be TASK_TRACED so we can use wake_up_state(__TASK_TRACED). If sys_ptrace() races with SIGKILL we do not need the extra and potentionally spurious wakeup. If the caller is PTRACE_KILL, wake_up_process() is even more wrong. The tracee can sleep in any state in any place, and if we have a buggy code which doesn't handle a spurious wakeup correctly PTRACE_KILL can be used to exploit it. For example: int main(void) { int child, status; child = fork(); if (!child) { int ret; assert(ptrace(PTRACE_TRACEME, 0,0,0) == 0); ret = pause(); printf("pause: %d %m\n", ret); return 0x23; } sleep(1); assert(ptrace(PTRACE_KILL, child, 0,0) == 0); assert(child == wait(&status)); printf("wait: %x\n", status); return 0; } prints "pause: -1 Unknown error 514", -ERESTARTNOHAND leaks to the userland. In this case sys_pause() is buggy as well and should be fixed. I do not know what was the original rationality behind PTRACE_KILL. The man page is simply wrong and afaics it was always wrong. Imho it should be deprecated, or may be it should do send_sig(SIGKILL) as Denys suggests, but in any case I do not think that the current behaviour was intentional. Note: there is another problem, ptrace_resume() changes ->exit_code and this can race with SIGKILL too. Eventually we should change ptrace to not use ->exit_code. Signed-off-by: Oleg Nesterov Signed-off-by: Paul Gortmaker --- kernel/ptrace.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/ptrace.c b/kernel/ptrace.c index b7b491e6c25b..9450ec22e5a6 100644 --- a/kernel/ptrace.c +++ b/kernel/ptrace.c @@ -507,7 +507,7 @@ static int ptrace_resume(struct task_struct *child, long request, long data) } child->exit_code = data; - wake_up_process(child); + wake_up_state(child, __TASK_TRACED); return 0; } -- 1.8.5.2 -- 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/