linux-kernel - [127/244] drivers/cpufreq/pcc-cpufreq.c: avoid NULL pointer dereference

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Date:	Wed, 28 Sep 2011 15:01:31 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Naga Chumbalkar <nagananda.chumbalkar@...com>,
	Dave Jones <davej@...emonkey.org.uk>,
	Len Brown <lenb@...nel.org>
Subject: [127/244] drivers/cpufreq/pcc-cpufreq.c: avoid NULL pointer dereference

3.0-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Naga Chumbalkar <nagananda.chumbalkar@...com>

commit e71f5cc402ecb42b407ae52add7b173bf1c53daa upstream.

per_cpu(processors, n) can be NULL, resulting in:

  Loading CPUFreq modules[  437.661360] BUG: unable to handle kernel NULL pointer dereference at (null)
  IP: [<ffffffffa0434314>] pcc_cpufreq_cpu_init+0x74/0x220 [pcc_cpufreq]

It's better to avoid the oops by failing the driver, and allowing the
system to boot.

Signed-off-by: Naga Chumbalkar <nagananda.chumbalkar@...com>
Cc: Dave Jones <davej@...emonkey.org.uk>
Cc: Len Brown <lenb@...nel.org>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 drivers/cpufreq/pcc-cpufreq.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/drivers/cpufreq/pcc-cpufreq.c
+++ b/drivers/cpufreq/pcc-cpufreq.c
@@ -261,6 +261,9 @@ static int pcc_get_offset(int cpu)
 	pr = per_cpu(processors, cpu);
 	pcc_cpu_data = per_cpu_ptr(pcc_cpu_info, cpu);
 
+	if (!pr)
+		return -ENODEV;
+
 	status = acpi_evaluate_object(pr->handle, "PCCP", NULL, &buffer);
 	if (ACPI_FAILURE(status))
 		return -ENODEV;


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