linux-kernel - [PATCH 7/9] ptrace: Simplify the wait_task_inactive call in ptrace_check

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Message-Id: <20220426225211.308418-7-ebiederm@xmission.com>
Date:   Tue, 26 Apr 2022 17:52:09 -0500
From:   "Eric W. Biederman" <ebiederm@...ssion.com>
To:     linux-kernel@...r.kernel.org
Cc:     rjw@...ysocki.net, Oleg Nesterov <oleg@...hat.com>,
        mingo@...nel.org, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, rostedt@...dmis.org, mgorman@...e.de,
        bigeasy@...utronix.de, Will Deacon <will@...nel.org>,
        tj@...nel.org, linux-pm@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Richard Weinberger <richard@....at>,
        Anton Ivanov <anton.ivanov@...bridgegreys.com>,
        Johannes Berg <johannes@...solutions.net>,
        linux-um@...ts.infradead.org, Chris Zankel <chris@...kel.net>,
        Max Filippov <jcmvbkbc@...il.com>,
        inux-xtensa@...ux-xtensa.org, Kees Cook <keescook@...omium.org>,
        Jann Horn <jannh@...gle.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>
Subject: [PATCH 7/9] ptrace: Simplify the wait_task_inactive call in ptrace_check_attach

Asking wait_task_inactive to verify that tsk->__state == __TASK_TRACED
was needed to detect the when ptrace_stop would decide not to stop
after calling "set_special_state(TASK_TRACED)".  With the recent
cleanups ptrace_stop will always stop after calling set_special_state.

Take advatnage of this by no longer asking wait_task_inactive to
verify the state.  If a bug is hit and wait_task_inactive does not
succeed warn and return -ESRCH.

Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
---
 kernel/ptrace.c | 14 +++-----------
 1 file changed, 3 insertions(+), 11 deletions(-)

diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 16d1a84a2cae..0634da7ac685 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -265,17 +265,9 @@ static int ptrace_check_attach(struct task_struct *child, bool ignore_state)
 	}
 	read_unlock(&tasklist_lock);
 
-	if (!ret && !ignore_state) {
-		if (!wait_task_inactive(child, __TASK_TRACED)) {
-			/*
-			 * This can only happen if may_ptrace_stop() fails and
-			 * ptrace_stop() changes ->state back to TASK_RUNNING,
-			 * so we should not worry about leaking __TASK_TRACED.
-			 */
-			WARN_ON(READ_ONCE(child->__state) == __TASK_TRACED);
-			ret = -ESRCH;
-		}
-	}
+	if (!ret && !ignore_state &&
+	    WARN_ON_ONCE(!wait_task_inactive(child, 0)))
+		ret = -ESRCH;
 
 	return ret;
 }
-- 
2.35.3