From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-19.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 34872C433B4 for ; Tue, 18 May 2021 01:10:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1528B613C3 for ; Tue, 18 May 2021 01:10:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345677AbhERBME (ORCPT ); Mon, 17 May 2021 21:12:04 -0400 Received: from mail.kernel.org ([198.145.29.99]:57814 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1345545AbhERBLg (ORCPT ); Mon, 17 May 2021 21:11:36 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id AA5EC613C1; Tue, 18 May 2021 01:10:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1621300219; bh=308Rgqzwzn8F6+BdjMW1/khn4yX6QfWk8pZLxSJPSbg=; h=From:To:Cc:Subject:Date:From; b=URmr45uXLYw/PScPtE0T753lKBNxFKJeP3Ia8T7MIXEUJK0SOiwoAM2hQrPRPYxsD 1Wu3og6nu6tPPYGlKAL5pLiEuj1XvMw7CWRqK/tzSuWoMl+zH+gAWyxab6vZqsw6Bn WiIRCjDkwVuK745Dq+YzSCslUzN1QLTHgpLYoNWxmsbt4t0+kULJM7J9CS+/sYrvi3 7CsSCAJTaqJ8jffnvCejifVfhgIMNRJBkgIa/0DsBIFvkX3f/yHGEo4MJLyS8/fIHa FDi1YGYaU4kZpmr9taI7uRGaAksDJ4s84bNSDeeeQsoVRTIh8mERjwGgr6l40FF8oU +ZqQ4K+u6WxnQ== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Oleg Nesterov , Simon Marchi , "Eric W. Biederman" , Pedro Alves , Jan Kratochvil , Linus Torvalds , Sasha Levin Subject: [PATCH AUTOSEL 4.4] ptrace: make ptrace() fail if the tracee changed its pid unexpectedly Date: Mon, 17 May 2021 21:10:17 -0400 Message-Id: <20210518011017.1486375-1-sashal@kernel.org> X-Mailer: git-send-email 2.30.2 MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Oleg Nesterov [ Upstream commit dbb5afad100a828c97e012c6106566d99f041db6 ] Suppose we have 2 threads, the group-leader L and a sub-theread T, both parked in ptrace_stop(). Debugger tries to resume both threads and does ptrace(PTRACE_CONT, T); ptrace(PTRACE_CONT, L); If the sub-thread T execs in between, the 2nd PTRACE_CONT doesn not resume the old leader L, it resumes the post-exec thread T which was actually now stopped in PTHREAD_EVENT_EXEC. In this case the PTHREAD_EVENT_EXEC event is lost, and the tracer can't know that the tracee changed its pid. This patch makes ptrace() fail in this case until debugger does wait() and consumes PTHREAD_EVENT_EXEC which reports old_pid. This affects all ptrace requests except the "asynchronous" PTRACE_INTERRUPT/KILL. The patch doesn't add the new PTRACE_ option to not complicate the API, and I _hope_ this won't cause any noticeable regression: - If debugger uses PTRACE_O_TRACEEXEC and the thread did an exec and the tracer does a ptrace request without having consumed the exec event, it's 100% sure that the thread the ptracer thinks it is targeting does not exist anymore, or isn't the same as the one it thinks it is targeting. - To some degree this patch adds nothing new. In the scenario above ptrace(L) can fail with -ESRCH if it is called after the execing sub-thread wakes the leader up and before it "steals" the leader's pid. Test-case: #include #include #include #include #include #include #include #include void *tf(void *arg) { execve("/usr/bin/true", NULL, NULL); assert(0); return NULL; } int main(void) { int leader = fork(); if (!leader) { kill(getpid(), SIGSTOP); pthread_t th; pthread_create(&th, NULL, tf, NULL); for (;;) pause(); return 0; } waitpid(leader, NULL, WSTOPPED); ptrace(PTRACE_SEIZE, leader, 0, PTRACE_O_TRACECLONE | PTRACE_O_TRACEEXEC); waitpid(leader, NULL, 0); ptrace(PTRACE_CONT, leader, 0,0); waitpid(leader, NULL, 0); int status, thread = waitpid(-1, &status, 0); assert(thread > 0 && thread != leader); assert(status == 0x80137f); ptrace(PTRACE_CONT, thread, 0,0); /* * waitid() because waitpid(leader, &status, WNOWAIT) does not * report status. Why ???? * * Why WEXITED? because we have another kernel problem connected * to mt-exec. */ siginfo_t info; assert(waitid(P_PID, leader, &info, WSTOPPED|WEXITED|WNOWAIT) == 0); assert(info.si_pid == leader && info.si_status == 0x0405); /* OK, it sleeps in ptrace(PTRACE_EVENT_EXEC == 0x04) */ assert(ptrace(PTRACE_CONT, leader, 0,0) == -1); assert(errno == ESRCH); assert(leader == waitpid(leader, &status, WNOHANG)); assert(status == 0x04057f); assert(ptrace(PTRACE_CONT, leader, 0,0) == 0); return 0; } Signed-off-by: Oleg Nesterov Reported-by: Simon Marchi Acked-by: "Eric W. Biederman" Acked-by: Pedro Alves Acked-by: Simon Marchi Acked-by: Jan Kratochvil Signed-off-by: Linus Torvalds Signed-off-by: Sasha Levin --- kernel/ptrace.c | 18 +++++++++++++++++- 1 file changed, 17 insertions(+), 1 deletion(-) diff --git a/kernel/ptrace.c b/kernel/ptrace.c index da8c358930fb..5a1d8cc7ef4e 100644 --- a/kernel/ptrace.c +++ b/kernel/ptrace.c @@ -129,6 +129,21 @@ void __ptrace_unlink(struct task_struct *child) spin_unlock(&child->sighand->siglock); } +static bool looks_like_a_spurious_pid(struct task_struct *task) +{ + if (task->exit_code != ((PTRACE_EVENT_EXEC << 8) | SIGTRAP)) + return false; + + if (task_pid_vnr(task) == task->ptrace_message) + return false; + /* + * The tracee changed its pid but the PTRACE_EVENT_EXEC event + * was not wait()'ed, most probably debugger targets the old + * leader which was destroyed in de_thread(). + */ + return true; +} + /* Ensure that nothing can wake it up, even SIGKILL */ static bool ptrace_freeze_traced(struct task_struct *task) { @@ -139,7 +154,8 @@ static bool ptrace_freeze_traced(struct task_struct *task) return ret; spin_lock_irq(&task->sighand->siglock); - if (task_is_traced(task) && !__fatal_signal_pending(task)) { + if (task_is_traced(task) && !looks_like_a_spurious_pid(task) && + !__fatal_signal_pending(task)) { task->state = __TASK_TRACED; ret = true; } -- 2.30.2