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Groups > linux.kernel > #1659104

[PATCH 18/26] wait: Fix WSTOPPED on a ptraced child

From "Eric W. Biederman" <ebiederm@xmission.com>
Newsgroups linux.kernel
Subject [PATCH 18/26] wait: Fix WSTOPPED on a ptraced child
Date 2017-06-06 21:20 +0200
Message-ID <tPsbi-4vm-83@gated-at.bofh.it> (permalink)
References <tPs1B-4ry-43@gated-at.bofh.it> <tPsbf-4vm-1@gated-at.bofh.it>
Organization linux.* mail to news gateway

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When ptracing waitpid(pid, WUNTRACED) has two possible meanings.
- Wait for ptrace stops from the task with tid == pid
- Wait for ordinary stops from the process with tgid == pid

The only sensible behavior and the Linux behavior in 2.2 and
2.4 has been to consume both ptrace stops and group stops
in this case.  It looks like when Oleg disentangled thread
stops and group stops in 2.6.30 fixing a lot of other issues
the case when we want to reap both was overlooked.

Consume both the group and the ptrace stop state when
waitpid(pid, WUNTRACED) could be asking for both, and
the wait status for both is idenitical.  This keeps
us from double reporting the stop and causing confusion.

This is very slight user visible change and is only visible
in the unlikely case a ptracer specifies WUNTRACED aka
WSTOPPED.

Write this code in such a way that it doesn't matter which
list we are traversing when we find a child whose stop states
we care about.

Fixes: 90bc8d8b1a38 ("do_wait: fix waiting for the group stop with the dead leader")
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
 kernel/exit.c | 82 +++++++++++++++++++++++++++++------------------------------
 1 file changed, 40 insertions(+), 42 deletions(-)

diff --git a/kernel/exit.c b/kernel/exit.c
index ff2ed1d60a8c..4e2d2b6f5581 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -1151,22 +1151,23 @@ static int wait_task_zombie(struct wait_opts *wo, int old_state, struct task_str
 	return retval;
 }
 
-static int *task_stopped_code(struct task_struct *p, bool ptrace)
+static int *task_trace_stopped_code(struct task_struct *p)
 {
-	if (ptrace) {
-		if (task_is_traced(p) && !(p->jobctl & JOBCTL_LISTENING))
-			return &p->exit_code;
-	} else {
-		if (p->signal->flags & SIGNAL_STOP_STOPPED)
-			return &p->signal->group_exit_code;
-	}
+	if (task_is_traced(p) && !(p->jobctl & JOBCTL_LISTENING))
+		return &p->exit_code;
+	return NULL;
+}
+
+static int *task_group_stopped_code(struct task_struct *p)
+{
+	if (p->signal->flags & SIGNAL_STOP_STOPPED)
+		return &p->signal->group_exit_code;
 	return NULL;
 }
 
 /**
  * wait_task_stopped - Wait for %TASK_STOPPED or %TASK_TRACED
  * @wo: wait options
- * @ptrace: is the wait for ptrace
  * @p: task to wait for
  *
  * Handle sys_wait4() work for %p in state %TASK_STOPPED or %TASK_TRACED.
@@ -1181,49 +1182,47 @@ static int *task_stopped_code(struct task_struct *p, bool ptrace)
  * success, implies that tasklist_lock is released and wait condition
  * search should terminate.
  */
-static int wait_task_stopped(struct wait_opts *wo,
-				int ptrace, struct task_struct *p)
+static int wait_task_stopped(struct wait_opts *wo, struct task_struct *p)
 {
 	struct siginfo __user *infop;
-	int retval, exit_code, *p_code, why;
-	uid_t uid = 0; /* unneeded, required by compiler */
+	int retval, exit_code, *p_code, *g_code, why;
+	bool group, gstop, pstop;
+	uid_t uid;
 	pid_t pid;
 
 	/*
-	 * Hide group stop state from real parent; otherwise a single
-	 * stop can be reported twice as group and ptrace stop.  If a
-	 * ptracer wants to distinguish these two events for its own
-	 * children it should create a separate process which takes the
-	 * role of real parent.
-	 */
-	if (!ptrace && p->ptrace && !ptrace_reparented(p))
-		ptrace = 1;
-
-	/*
 	 * Traditionally we see ptrace'd stopped tasks regardless of options.
 	 */
-	if (!ptrace && !(wo->wo_flags & WUNTRACED))
+	group = thread_group_leader(p) && !ptrace_reparented(p);
+	pstop = same_thread_group(current, p->parent);
+	gstop = group && (wo->wo_flags & WUNTRACED);
+	if (!pstop && !gstop)
 		return 0;
 
-	if (!task_stopped_code(p, ptrace))
+	if ((!pstop || !task_trace_stopped_code(p)) &&
+	    (!gstop || !task_group_stopped_code(p)))
 		return 0;
 
 	exit_code = 0;
 	spin_lock_irq(&p->sighand->siglock);
 
-	p_code = task_stopped_code(p, ptrace);
-	if (unlikely(!p_code))
-		goto unlock_sig;
-
-	exit_code = *p_code;
-	if (!exit_code)
-		goto unlock_sig;
-
-	if (!unlikely(wo->wo_flags & WNOWAIT))
-		*p_code = 0;
-
-	uid = from_kuid_munged(current_user_ns(), task_uid(p));
-unlock_sig:
+	p_code = g_code = NULL;
+	if (pstop)
+		p_code = task_trace_stopped_code(p);
+	if (gstop)
+		g_code = task_group_stopped_code(p);
+	if (p_code) {
+		exit_code = *p_code;
+		why = CLD_TRAPPED;
+		if (!(wo->wo_flags & WNOWAIT))
+			*p_code = 0;
+	}
+	if (g_code && (!exit_code || (*g_code == exit_code))) {
+		exit_code = *g_code;
+		why = CLD_STOPPED;
+		if (!(wo->wo_flags & WNOWAIT))
+			*g_code = 0;
+	}
 	spin_unlock_irq(&p->sighand->siglock);
 	if (!exit_code)
 		return 0;
@@ -1236,8 +1235,8 @@ static int wait_task_stopped(struct wait_opts *wo,
 	 * possibly take page faults for user memory.
 	 */
 	get_task_struct(p);
+	uid = from_kuid_munged(current_user_ns(), task_uid(p));
 	pid = task_pid_vnr(p);
-	why = ptrace ? CLD_TRAPPED : CLD_STOPPED;
 	read_unlock(&tasklist_lock);
 	sched_annotate_sleep();
 
@@ -1403,10 +1402,9 @@ static int wait_consider_task(struct wait_opts *wo, int ptrace,
 	}
 
 	/*
-	 * Wait for stopped.  Depending on @ptrace, different stopped state
-	 * is used and the two don't interact with each other.
+	 * Wait for stopped.
 	 */
-	ret = wait_task_stopped(wo, ptrace, p);
+	ret = wait_task_stopped(wo, p);
 	if (ret)
 		return ret;
 
-- 
2.10.1

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Thread

[PATCH 00/26] Fixing wait, exit, ptrace, exec, and CLONE_THREAD ebiederm@xmission.com (Eric W. Biederman) - 2017-06-06 21:10 +0200
  [PATCH 01/26] alpha: Remove unused TASK_GROUP_LEADER "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
    [PATCH 12/26] wait: Directly test for the two cases where wait_task_zombie is called "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
    [PATCH 15/26] wait: Don't delay !ptrace_reparented leaders "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
    [PATCH 13/26] wait: Remove unused delay_group_leader "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
    [PATCH 17/26] exit: Rework the exit states for ptracees "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
    [PATCH 20/26] wait: Don't pass the list to wait_consider_task "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
    [PATCH 26/26] pidns: Ensure zap_pid_ns_processes always terminates "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
    [PATCH 19/26] wait: Simpler code for clearing notask_error in wait_consider_task "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
    [PATCH 24/26] signal: In ptrace_stop improve identical signal detection "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
    [PATCH 09/26] signal: Don't allow sending SIGKILL or SIGSTOP to init "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
    [PATCH 03/26] signal: Do not perform permission checks when sending pdeath_signal "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
      Re: [PATCH 03/26] signal: Do not perform permission checks when  sending pdeath_signal Linus Torvalds <torvalds@linux-foundation.org> - 2017-06-06 22:10 +0200
        Re: [PATCH 03/26] signal: Do not perform permission checks when sending pdeath_signal ebiederm@xmission.com (Eric W. Biederman) - 2017-06-07 13:40 +0200
      Re: [PATCH 03/26] signal: Do not perform permission checks when  sending pdeath_signal Richard Weinberger <richard.weinberger@gmail.com> - 2017-06-06 23:50 +0200
    [PATCH 07/26] pidns: Improve the error handling in alloc_pid "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
    [PATCH 22/26] exit: Fix auto-wait of ptraced children "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
    [PATCH 02/26] cgroup: Don't open code tasklist_empty() "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
    [PATCH 04/26] signal: Make group_send_sig_info static "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
    [PATCH 23/26] signal:  Fix SIGCONT before group stop completes. "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
    [PATCH 18/26] wait: Fix WSTOPPED on a ptraced child "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
    [PATCH 10/26] ptrace: Simplify ptrace_detach & exit_ptrace "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
    [PATCH 21/26] wait: Optmize waitpid "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
    [PATCH 14/26] wait: Move changing of ptrace from wait_consider_task into wait_task_stopped "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
    [PATCH 08/26] exit: Make the runqueue rcu safe "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
      Re: [PATCH 08/26] exit: Make the runqueue rcu safe Oleg Nesterov <oleg@redhat.com> - 2017-06-07 15:20 +0200
    [PATCH 06/26] rlimit: Remove unnecessary grab of tasklist_lock "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
      Re: [PATCH 06/26] rlimit: Remove unnecessary grab of tasklist_lock Oleg Nesterov <oleg@redhat.com> - 2017-06-07 14:40 +0200
        Re: [PATCH 06/26] rlimit: Remove unnecessary grab of tasklist_lock ebiederm@xmission.com (Eric W. Biederman) - 2017-06-07 16:20 +0200
    [PATCH 16/26] exit: Fix reporting a ptraced !reparented leader has exited "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
    [PATCH 11/26] wait: Properly implement __WCLONE handling in the presence of exec and ptrace "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
    [PATCH 05/26] exit:  Remove the pointless clearing of SIGPENDING in __exit_signal "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
    [PATCH 25/26] signal: In ptrace_stop use CLD_TRAPPED in all ptrace signals "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:30 +0200
  Re: [PATCH 00/26] Fixing wait, exit, ptrace, exec, and CLONE_THREAD Aleksa Sarai <asarai@suse.de> - 2017-06-06 21:50 +0200
    Re: [PATCH 00/26] Fixing wait, exit, ptrace, exec, and CLONE_THREAD ebiederm@xmission.com (Eric W. Biederman) - 2017-06-07 13:50 +0200
      Re: [PATCH 00/26] Fixing wait, exit, ptrace, exec, and CLONE_THREAD Aleksa Sarai <asarai@suse.de> - 2017-06-07 14:30 +0200
  Re: [PATCH 00/26] Fixing wait, exit, ptrace, exec, and CLONE_THREAD Linus Torvalds <torvalds@linux-foundation.org> - 2017-06-06 22:10 +0200
    Re: [PATCH 00/26] Fixing wait, exit, ptrace, exec, and CLONE_THREAD ebiederm@xmission.com (Eric W. Biederman) - 2017-06-07 18:10 +0200

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