[4.2.y-ckt stable] Patch "x86/irq: Fix a race in x86_vector_free_irqs()" has been added to the 4.2.y-ckt tree

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    x86/irq: Fix a race in x86_vector_free_irqs()

to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree 
which can be found at:

    https://git.launchpad.net/~canonical-kernel/linux/+git/linux-stable-ckt/log/?h=linux-4.2.y-queue

This patch is scheduled to be released in version 4.2.8-ckt10.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 4.2.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

---8<------------------------------------------------------------

>From 52f980c88ba3278a419c1ed908f9d8c255a6be5d Mon Sep 17 00:00:00 2001
From: Jiang Liu <jiang.liu at linux.intel.com>
Date: Thu, 31 Dec 2015 16:30:44 +0000
Subject: x86/irq: Fix a race in x86_vector_free_irqs()

commit 111abeba67e0dbdc26537429de9155e4f1d807d8 upstream.

There's a race condition between

x86_vector_free_irqs()
{
	free_apic_chip_data(irq_data->chip_data);
	xxxxx	//irq_data->chip_data has been freed, but the pointer
		//hasn't been reset yet
	irq_domain_reset_irq_data(irq_data);
}

and

smp_irq_move_cleanup_interrupt()
{
	raw_spin_lock(&vector_lock);
	data = apic_chip_data(irq_desc_get_irq_data(desc));
	access data->xxxx	// may access freed memory
	raw_spin_unlock(&desc->lock);
}

which may cause smp_irq_move_cleanup_interrupt() to access freed memory.

Call irq_domain_reset_irq_data(), which clears the pointer with vector lock
held.

[ tglx: Free memory outside of lock held region. ]

Signed-off-by: Jiang Liu <jiang.liu at linux.intel.com>
Tested-by: Borislav Petkov <bp at alien8.de>
Tested-by: Joe Lawrence <joe.lawrence at stratus.com>
Cc: Jeremiah Mahler <jmmahler at gmail.com>
Cc: andy.shevchenko at gmail.com
Cc: Guenter Roeck <linux at roeck-us.net>
Link: http://lkml.kernel.org/r/1450880014-11741-3-git-send-email-jiang.liu@linux.intel.com
Signed-off-by: Thomas Gleixner <tglx at linutronix.de>
[ kamal: backport to 4.2-stable; prereq for
  1bdb897 x86/apic: Handle zero vector gracefully in clear_vector_irq() ]
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 arch/x86/kernel/apic/vector.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kernel/apic/vector.c b/arch/x86/kernel/apic/vector.c
index ea4ba83..7889bec 100644
--- a/arch/x86/kernel/apic/vector.c
+++ b/arch/x86/kernel/apic/vector.c
@@ -225,9 +225,7 @@ static int assign_irq_vector_policy(int irq, int node,
 static void clear_irq_vector(int irq, struct apic_chip_data *data)
 {
 	int cpu, vector;
-	unsigned long flags;

-	raw_spin_lock_irqsave(&vector_lock, flags);
 	BUG_ON(!data->cfg.vector);

 	vector = data->cfg.vector;
@@ -237,10 +235,8 @@ static void clear_irq_vector(int irq, struct apic_chip_data *data)
 	data->cfg.vector = 0;
 	cpumask_clear(data->domain);

-	if (likely(!data->move_in_progress)) {
-		raw_spin_unlock_irqrestore(&vector_lock, flags);
+	if (likely(!data->move_in_progress))
 		return;
-	}

 	for_each_cpu_and(cpu, data->old_domain, cpu_online_mask) {
 		for (vector = FIRST_EXTERNAL_VECTOR; vector < NR_VECTORS;
@@ -252,7 +248,6 @@ static void clear_irq_vector(int irq, struct apic_chip_data *data)
 		}
 	}
 	data->move_in_progress = 0;
-	raw_spin_unlock_irqrestore(&vector_lock, flags);
 }

 void init_irq_alloc_info(struct irq_alloc_info *info,
@@ -273,19 +268,24 @@ void copy_irq_alloc_info(struct irq_alloc_info *dst, struct irq_alloc_info *src)
 static void x86_vector_free_irqs(struct irq_domain *domain,
 				 unsigned int virq, unsigned int nr_irqs)
 {
+	struct apic_chip_data *apic_data;
 	struct irq_data *irq_data;
+	unsigned long flags;
 	int i;

 	for (i = 0; i < nr_irqs; i++) {
 		irq_data = irq_domain_get_irq_data(x86_vector_domain, virq + i);
 		if (irq_data && irq_data->chip_data) {
+			raw_spin_lock_irqsave(&vector_lock, flags);
 			clear_irq_vector(virq + i, irq_data->chip_data);
-			free_apic_chip_data(irq_data->chip_data);
+			apic_data = irq_data->chip_data;
+			irq_domain_reset_irq_data(irq_data);
+			raw_spin_unlock_irqrestore(&vector_lock, flags);
+			free_apic_chip_data(apic_data);
 #ifdef	CONFIG_X86_IO_APIC
 			if (virq + i < nr_legacy_irqs())
 				legacy_irq_data[virq + i] = NULL;
 #endif
-			irq_domain_reset_irq_data(irq_data);
 		}
 	}
 }
--
2.7.4