perf: Prevent divide by zero exception in kernel/events/core.c

PATCH In review Knut Petersen 3 participants 4 messages Sep 25, 2013 – Oct 4, 2013

Subsystems (2)

perf events Proc sysctl

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Knut Petersen

author

2013-09-25 12:07 UTC #0 lore raw

PATCH 1/1 perf: Prevent divide by zero exception in kernel/events/core.c

Any value written to /proc/sys/kernel/perf_event_max_sample_rate is accepted and used as a divisor in perf_proc_update_handler().

Obviously that is wrong. 0 will cause a divide by 0 exception, and negative values are unreasonable.

The attached patch enforces a lower limit of 1.

cu,
Knut

Quoted 1 line

From 7f468bd7bad2f2fec2e93c89a48008d1cba99001 Mon Sep 17 00:00:00 2001

From: Knut Petersen <[email protected]>
Date: Wed, 25 Sep 2013 13:34:57 +0200
Subject: [PATCH] Enforce 1 as lower limit for perf_event_max_sample_rate

/proc/sys/kernel/perf_event_max_sample_rate will accept negative values as well as 0.

Negative values are unreasonable, and 0 causes a divide by zero exception in perf_proc_update_handler.

This patch enforces a lower limit of 1.

Signed-off-by Knut Petersen <[email protected]>

---
 kernel/events/core.c | 3 +++
 1 file changed, 3 insertions(+)

kernel/events/core.c +3 -0

index dd236b6..350bb53 100644
@@ -198,6 +198,9 @@ int perf_proc_update_handler(struct ctl_table *table, int write,
 	if (ret || !write)
 		return ret;
 
+	if (sysctl_perf_event_sample_rate <= 0)
+		sysctl_perf_event_sample_rate = 1;
+
 	max_samples_per_tick = DIV_ROUND_UP(sysctl_perf_event_sample_rate, HZ);
 	perf_sample_period_ns = NSEC_PER_SEC / sysctl_perf_event_sample_rate;
 	update_perf_cpu_limits();

Signature · 1 line

1.8.1.4

Peter Zijlstra

maintainer

2013-09-25 12:13 UTC #1 lore raw

Quoted 22 lines · Knut Petersen

From: Knut Petersen <[email protected]>
Date: Wed, 25 Sep 2013 13:34:57 +0200
Subject: [PATCH] Enforce 1 as lower limit for perf_event_max_sample_rate
/proc/sys/kernel/perf_event_max_sample_rate will accept negative values as well as 0.
Negative values are unreasonable, and 0 causes a divide by zero exception in perf_proc_update_handler.
This patch enforces a lower limit of 1.
Signed-off-by Knut Petersen <[email protected]>
---
 kernel/events/core.c | 3 +++
 1 file changed, 3 insertions(+)
kernel/events/core.c +0 -0
index dd236b6..350bb53 100644

kernel/events/core.c int perf_proc_update_handler(struct ctl_table *table, int write, · line 206

Quoted 9 lines

kernel/events/core.c +3 -0

@@ -198,6 +198,9 @@ int perf_proc_update_handler(struct ctl_table *table, int write,
 	if (ret || !write)
 		return ret;
 
+	if (sysctl_perf_event_sample_rate <= 0)
+		sysctl_perf_event_sample_rate = 1;
+
 	max_samples_per_tick = DIV_ROUND_UP(sysctl_perf_event_sample_rate, HZ);
 	perf_sample_period_ns = NSEC_PER_SEC / sysctl_perf_event_sample_rate;
 	update_perf_cpu_limits();

The 'normal' way of doing that is changing the sysctl table entry to use proc_dointvec_minmax and set .extra = &one. See for example &sysctl_sched_cfs_bandwidth_slice in kernel/sysctl.c

Knut Petersen

author

2013-09-25 12:46 UTC #2 lore raw

Quoted 3 lines · Peter Zijlstra

The 'normal' way of doing that is changing the sysctl table entry to use proc_dointvec_minmax and set .extra = &one. See for example &sysctl_sched_cfs_bandwidth_slice in kernel/sysctl.c

Thanks. V2 attached.

cu,
Knut

Quoted 1 line

From 4ef9dabdd27a02e2ebd45c2d98afda7e43e82ab3 Mon Sep 17 00:00:00 2001

From: Knut Petersen <[email protected]>
Date: Wed, 25 Sep 2013 14:29:37 +0200
Subject: [PATCH] Enforce 1 as lower limit for perf_event_max_sample_rate

/proc/sys/kernel/perf_event_max_sample_rate will accept negative values as well as 0.

Negative values are unreasonable, and 0 causes a divide by zero exception in perf_proc_update_handler.

This patch enforces a lower limit of 1.

v2: Use proc_dointvec_minmax() as suggested by Peter Zijlstra.

Signed-off-by Knut Petersen <[email protected]>

---
 kernel/events/core.c | 2 +-
 kernel/sysctl.c      | 1 +
 2 files changed, 2 insertions(+), 1 deletion(-)

kernel/events/core.c +1 -1

index dd236b6..8721a17 100644
@@ -193,7 +193,7 @@ int perf_proc_update_handler(struct ctl_table *table, int write,
 		void __user *buffer, size_t *lenp,
 		loff_t *ppos)
 {
-	int ret = proc_dointvec(table, write, buffer, lenp, ppos);
+	int ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 
 	if (ret || !write)
 		return ret;

kernel/sysctl.c +1 -0

index b2f06f3..2a9db91 100644
@@ -1049,6 +1049,7 @@ static struct ctl_table kern_table[] = {
 		.maxlen		= sizeof(sysctl_perf_event_sample_rate),
 		.mode		= 0644,
 		.proc_handler	= perf_proc_update_handler,
+		.extra1		= &one,
 	},
 	{
 		.procname	= "perf_cpu_time_max_percent",

Signature · 1 line

1.8.1.4

tip-bot for Knut Petersen

merge bot

2013-10-04 17:32 UTC #3 lore raw

[tip:perf/core] perf: Enforce 1 as lower limit for perf_event_max_sample_rate

perf: Enforce 1 as lower limit for perf_event_max_sample_rate

Commit-ID:  723478c8a471403c53cf144999701f6e0c4bbd11
Gitweb:     http://git.kernel.org/tip/723478c8a471403c53cf144999701f6e0c4bbd11
Author:     Knut Petersen <[email protected]>
AuthorDate: Wed, 25 Sep 2013 14:29:37 +0200
Committer:  Ingo Molnar <[email protected]>
CommitDate: Fri, 4 Oct 2013 10:06:07 +0200

perf: Enforce 1 as lower limit for perf_event_max_sample_rate

/proc/sys/kernel/perf_event_max_sample_rate will accept negative values as well as 0.

Negative values are unreasonable, and 0 causes a divide by zero exception in perf_proc_update_handler.

This patch enforces a lower limit of 1.

Signed-off-by Knut Petersen <[email protected]>

Signed-off-by Peter Zijlstra <[email protected]>

Link http://lkml.kernel.org/r/[email protected] open here

Signed-off-by Ingo Molnar <[email protected]>

---
 kernel/events/core.c | 2 +-
 kernel/sysctl.c      | 1 +
 2 files changed, 2 insertions(+), 1 deletion(-)

kernel/events/core.c +1 -1

index d49a9d2..b25d65c 100644
@@ -193,7 +193,7 @@ int perf_proc_update_handler(struct ctl_table *table, int write,
 		void __user *buffer, size_t *lenp,
 		loff_t *ppos)
 {
-	int ret = proc_dointvec(table, write, buffer, lenp, ppos);
+	int ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 
 	if (ret || !write)
 		return ret;

kernel/sysctl.c +1 -0

index b2f06f3..2a9db91 100644
@@ -1049,6 +1049,7 @@ static struct ctl_table kern_table[] = {
 		.maxlen		= sizeof(sysctl_perf_event_sample_rate),
 		.mode		= 0644,
 		.proc_handler	= perf_proc_update_handler,
+		.extra1		= &one,
 	},
 	{
 		.procname	= "perf_cpu_time_max_percent",