linux-kernel - [PATCH] ptrace: fix clearing of JOBCTL_TRACED in ptrace_unfreeze

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Date:   Wed,  6 Jul 2022 12:16:25 +0200
From:   Sven Schnelle <svens@...ux.ibm.com>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Kees Cook <keescook@...omium.org>, linux-kernel@...r.kernel.org
Subject: [PATCH] ptrace: fix clearing of JOBCTL_TRACED in ptrace_unfreeze_traced()

CI reported the following splat while running the strace testsuite:

[ 3976.640309] WARNING: CPU: 1 PID: 3570031 at kernel/ptrace.c:272 ptrace_check_attach+0x12e/0x178
[ 3976.640391] CPU: 1 PID: 3570031 Comm: strace Tainted: G           OE     5.19.0-20220624.rc3.git0.ee819a77d4e7.300.fc36.s390x #1
[ 3976.640410] Hardware name: IBM 3906 M04 704 (z/VM 7.1.0)
[ 3976.640452] Call Trace:
[ 3976.640454]  [<00000000ab4b645a>] ptrace_check_attach+0x132/0x178
[ 3976.640457] ([<00000000ab4b6450>] ptrace_check_attach+0x128/0x178)
[ 3976.640460]  [<00000000ab4b6cde>] __s390x_sys_ptrace+0x86/0x160
[ 3976.640463]  [<00000000ac03fcec>] __do_syscall+0x1d4/0x200
[ 3976.640468]  [<00000000ac04e312>] system_call+0x82/0xb0
[ 3976.640470] Last Breaking-Event-Address:
[ 3976.640471]  [<00000000ab4ea3c8>] wait_task_inactive+0x98/0x190

This is because JOBCTL_TRACED is set, but the task is not in TASK_TRACED
state. Caused by ptrace_unfreeze_traced() which does:

task->jobctl &= ~TASK_TRACED

but it should be:

task->jobctl &= ~JOBCTL_TRACED

Fixes: 31cae1eaae4f ("sched,signal,ptrace: Rework TASK_TRACED, TASK_STOPPED state")
Signed-off-by: Sven Schnelle <svens@...ux.ibm.com>
---
 kernel/ptrace.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 156a99283b11..1893d909e45c 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -222,7 +222,7 @@ static void ptrace_unfreeze_traced(struct task_struct *task)
 	if (lock_task_sighand(task, &flags)) {
 		task->jobctl &= ~JOBCTL_PTRACE_FROZEN;
 		if (__fatal_signal_pending(task)) {
-			task->jobctl &= ~TASK_TRACED;
+			task->jobctl &= ~JOBCTL_TRACED;
 			wake_up_state(task, __TASK_TRACED);
 		}
 		unlock_task_sighand(task, &flags);
-- 
2.34.1