linux-kernel - [PATCH 1/2] perf_event: Fix incorrect range check on cpu number

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Date:	Tue, 15 Dec 2009 19:40:32 +1100
From:	Paul Mackerras <paulus@...ba.org>
To:	Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org, Michael Neuling <mikey@...ling.org>
Subject: [PATCH 1/2] perf_event: Fix incorrect range check on cpu number

It is quite legitimate for CPUs to be numbered sparsely, meaning that
it possible for an online CPU to have a number which is greater than
the total count of possible CPUs.

Currently find_get_context() has a sanity check on the cpu number
where it checks it against num_possible_cpus().  This test can fail
for a legitimate cpu number if the cpu_possible_mask is sparsely
populated.

This fixes the problem by checking the CPU number against
nr_cpumask_bits instead, since that is the appropriate check to ensure
that the cpu number is same to pass to cpu_isset() subsequently.

Reported-by: Michael Neuling <mikey@...ling.org>
Tested-by: Michael Neuling <mikey@...ling.org>
Cc: stable@...nel.org
Signed-off-by: Paul Mackerras <paulus@...ba.org>
---
 kernel/perf_event.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 6b7ddba..78551b3 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -1604,7 +1604,7 @@ static struct perf_event_context *find_get_context(pid_t pid, int cpu)
 		if (perf_paranoid_cpu() && !capable(CAP_SYS_ADMIN))
 			return ERR_PTR(-EACCES);

-		if (cpu < 0 || cpu > num_possible_cpus())
+		if (cpu < 0 || cpu >= nr_cpumask_bits)
 			return ERR_PTR(-EINVAL);

 		/*
--
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