linux-kernel - [PATCH 5/7] kprobes: Do not try to disarm already disarmed Kprobe

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Message-Id: <1424967232-2923-6-git-send-email-pmladek@suse.cz>
Date:	Thu, 26 Feb 2015 17:13:50 +0100
From:	Petr Mladek <pmladek@...e.cz>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	"David S. Miller" <davem@...emloft.net>,
	Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Ingo Molnar <mingo@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Jiri Kosina <jkosina@...e.cz>, linux-kernel@...r.kernel.org,
	Petr Mladek <pmladek@...e.cz>
Subject: [PATCH 5/7] kprobes: Do not try to disarm already disarmed Kprobe

The global kprobes_all_disarmed flag says that all Kprobes are disarmed
even when they are marked as enabled. This is properly handled in
register_kprobe() but it is ignored in __disable_kprobe().

This problem gets more serious after we started handling errors from
disarm_kprobe(). The second disarming fails and we do not longer
set KPROBE_FLAG_DISABLED. It might trigger BUG_ON(!kprobe_disarmed(ap))
in __unregister_kprobe_top() even when Kprobes were globally
disarmed.

Well, kprobe_disarmed(ap) should return false when the global
kprobes_all_disarmed flag is set. But let's solve this separately.

This patch fixes __disable_kprobe(), so that it does not disarm
when the Kprobe is not armed.

Note that I reverted the condition "if (kprobe_disabled(p))" and used "goto
out" there. It helped to keep the code nesting on a reasonable level.

Signed-off-by: Petr Mladek <pmladek@...e.cz>
---
 kernel/kprobes.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 1fcb19095b43..54bc2a6960b4 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1594,22 +1594,25 @@ static struct kprobe *__disable_kprobe(struct kprobe *p)
 	if (unlikely(orig_p == NULL))
 		return ERR_PTR(-EINVAL);
 
-	if (!kprobe_disabled(p)) {
-		/* Disable probe if it is a child probe */
-		if (p != orig_p)
-			p->flags |= KPROBE_FLAG_DISABLED;
+	if (kprobe_disabled(p))
+		goto out;
+
+	/* Disable probe if it is a child probe */
+	if (p != orig_p)
+		p->flags |= KPROBE_FLAG_DISABLED;
 
-		/* Try to disarm and disable this/parent probe */
-		if (p == orig_p || aggr_kprobe_disabled(orig_p)) {
+	/* Try to disarm and disable this/parent probe */
+	if (p == orig_p || aggr_kprobe_disabled(orig_p)) {
+		if (!kprobes_all_disarmed) {
 			err = disarm_kprobe(orig_p, true);
 			if (err) {
 				p->flags &= ~KPROBE_FLAG_DISABLED;
 				return ERR_PTR(err);
 			}
-			orig_p->flags |= KPROBE_FLAG_DISABLED;
 		}
+		orig_p->flags |= KPROBE_FLAG_DISABLED;
 	}
-
+out:
 	return orig_p;
 }
 
-- 
1.8.5.6

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