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

From: David Vrabel
Date: Mon Jan 05 2015 - 08:20:04 EST


On 05/01/15 13:06, Vitaly Kuznetsov wrote:
> 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.

Add Reported-by: Laszlo ... tag perhaps?

> --- 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;

struct xen_clock_event_device *xevt = ...;

> 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);

Use sizeof(xevt->name) here.

David
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