linux-kernel - [PATCH 25/26] signal: In ptrace_stop use CLD

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Date:   Tue,  6 Jun 2017 14:03:37 -0500
From:   "Eric W. Biederman" <ebiederm@...ssion.com>
To:     linux-kernel@...r.kernel.org
Cc:     linux-api@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Kees Cook <keescook@...omium.org>,
        Roland McGrath <roland@...k.frob.com>,
        Al Viro <viro@...IV.linux.org.uk>,
        David Howells <dhowells@...hat.com>,
        "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>
Subject: [PATCH 25/26] signal: In ptrace_stop use CLD_TRAPPED in all ptrace signals

If the only job of the signal is to report a ptrace level event set
si_code to CLD_TRAPPED instead of possibly CLD_STOPPED.

This causes the siginfo of the signals that are sent to match the
signinfo of the signals returned by waitid.

This is a user visible difference but I don't expect anything will
care.

In fact this is a return to historical linux behavior.  In linux 2.4.0
all ptrace stops were reported through do_notify_parent with
CLD_TRAPPED.  When do_notify_parent_cldstop was added the CLD_TRAPPED
logic was not included and CLD_TRAPPED for ptrace stops was lost.  As
nothing was said about this case I assume it was an oversight.

When waitid was added a little earlier all stops were being
reported with do_notify_parent and all ptrace stops were setting
CLD_TRAPPED.  So initially signals and waitid were in sync with
respect to setting CLD_TRAPPED.

It is also worth knowing that posix uses documents CLD_TRAPPED
as "Traced child has trapped."

History Tree: https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git
Ref: ca3f74aa7baa ("[PATCH] waitid system call")
Fixes: Fixes: ebf5ebe31d2c ("[PATCH] signal-fixes-2.5.59-A4")
Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
---
 kernel/signal.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/signal.c b/kernel/signal.c
index ff41e6ee2b5e..0d4ca87f1fee 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1886,9 +1886,9 @@ static void ptrace_stop(int exit_code, int why, int clear_code, siginfo_t *info)
 		 * separately unless they are going to be identical.
 		 */
 		if (!identical)
-			do_notify_parent_cldstop(current, true, why);
+			do_notify_parent_cldstop(current, true, CLD_TRAPPED);
 		if (gstop_done)
-			do_notify_parent_cldstop(current, false, why);
+			do_notify_parent_cldstop(current, false, CLD_STOPPED);
 
 		/*
 		 * Don't want to allow preemption here, because
@@ -1912,7 +1912,7 @@ static void ptrace_stop(int exit_code, int why, int clear_code, siginfo_t *info)
 		 * the real parent of the group stop completion is enough.
 		 */
 		if (gstop_done)
-			do_notify_parent_cldstop(current, false, why);
+			do_notify_parent_cldstop(current, false, CLD_STOPPED);
 
 		/* tasklist protects us from ptrace_freeze_traced() */
 		__set_current_state(TASK_RUNNING);
-- 
2.10.1