[Xen-devel] [PATCH] x86/xen: avoid freeing static 'name' when kasprintf() fails

[Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>]

In case kasprintf() fails in xen_setup_timer() we assign name to the static
string "<timer kasprintf failed>". We, however, don't check that fact before
issuing kfree() in xen_teardown_timer(), kernel is supposed to crash with
'kernel BUG at mm/slub.c:3341!'

Solve the issue by making name a fixed length string inside struct
xen_clock_event_device. 16 bytes should be enough.

The issue was discovered by Laszlo Ersek.

Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
---
 arch/x86/xen/time.c | 13 ++++---------
 1 file changed, 4 insertions(+), 9 deletions(-)

diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
index f473d26..221ebb6 100644
--- a/arch/x86/xen/time.c
+++ b/arch/x86/xen/time.c
@@ -391,7 +391,7 @@ static const struct clock_event_device *xen_clockevent =
 
 struct xen_clock_event_device {
        struct clock_event_device evt;
-       char *name;
+       char name[16];
 };
 static DEFINE_PER_CPU(struct xen_clock_event_device, xen_clock_events) = { 
.evt.irq = -1 };
 
@@ -420,14 +420,11 @@ void xen_teardown_timer(int cpu)
        if (evt->irq >= 0) {
                unbind_from_irqhandler(evt->irq, NULL);
                evt->irq = -1;
-               kfree(per_cpu(xen_clock_events, cpu).name);
-               per_cpu(xen_clock_events, cpu).name = NULL;
        }
 }
 
 void xen_setup_timer(int cpu)
 {
-       char *name;
        struct clock_event_device *evt;
        int irq;
 
@@ -438,21 +435,19 @@ void xen_setup_timer(int cpu)
 
        printk(KERN_INFO "installing Xen timer for CPU %d\n", cpu);
 
-       name = kasprintf(GFP_KERNEL, "timer%d", cpu);
-       if (!name)
-               name = "<timer kasprintf failed>";
+       snprintf(per_cpu(xen_clock_events, cpu).name, 16, "timer%d", cpu);
 
        irq = bind_virq_to_irqhandler(VIRQ_TIMER, cpu, xen_timer_interrupt,
                                      IRQF_PERCPU|IRQF_NOBALANCING|IRQF_TIMER|
                                      IRQF_FORCE_RESUME|IRQF_EARLY_RESUME,
-                                     name, NULL);
+                                     per_cpu(xen_clock_events, cpu).name,
+                                     NULL);
        (void)xen_set_irq_priority(irq, XEN_IRQ_PRIORITY_MAX);
 
        memcpy(evt, xen_clockevent, sizeof(*evt));
 
        evt->cpumask = cpumask_of(cpu);
        evt->irq = irq;
-       per_cpu(xen_clock_events, cpu).name = name;
 }
 
 
-- 
1.9.3


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