linux-kernel - [PATCH 3.12 018/111] perf: Limit perf_event_attr::sample

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Message-Id: <ed8acba3f62f4cb479628215582b487872c398d7.1403512281.git.jslaby@suse.cz>
Date:	Mon, 23 Jun 2014 10:30:53 +0200
From:	Jiri Slaby <jslaby@...e.cz>
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 018/111] perf: Limit perf_event_attr::sample_period to 63 bits

From: Peter Zijlstra <peterz@...radead.org>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

commit 0819b2e30ccb93edf04876237b6205eef84ec8d2 upstream.

Vince reported that using a large sample_period (one with bit 63 set)
results in wreckage since while the sample_period is fundamentally
unsigned (negative periods don't make sense) the way we implement
things very much rely on signed logic.

So limit sample_period to 63 bits to avoid tripping over this.

Reported-by: Vince Weaver <vincent.weaver@...ne.edu>
Signed-off-by: Peter Zijlstra <peterz@...radead.org>
Link: http://lkml.kernel.org/n/tip-p25fhunibl4y3qi0zuqmyf4b@git.kernel.org
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 kernel/events/core.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 6e0f9648fa68..01eeaf6cc95a 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6956,6 +6956,9 @@ SYSCALL_DEFINE5(perf_event_open,
 	if (attr.freq) {
 		if (attr.sample_freq > sysctl_perf_event_sample_rate)
 			return -EINVAL;
+	} else {
+		if (attr.sample_period & (1ULL << 63))
+			return -EINVAL;
 	}
 
 	/*
-- 
2.0.0

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