x86/xen: avoid freeing static 'name' when kasprintf() fails

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.

Suggested-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>

1 files changed, 5 insertions, 11 deletions

diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
index 23019b483908..69087341d9ae 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 };
 
@@ -420,39 +420,33 @@ 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;
+        struct xen_clock_event_device *xevt = &per_cpu(xen_clock_events, cpu);
+        struct clock_event_device *evt = &xevt->evt;
         int irq;
 
-        evt = &per_cpu(xen_clock_events, cpu).evt;
         WARN(evt->irq >= 0, "IRQ%d for CPU%d is already allocated\n", evt->irq, cpu);
         if (evt->irq >= 0)
                 xen_teardown_timer(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(xevt->name, sizeof(xevt->name), "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);
+                                      xevt->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;
 }