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Re: [libvirt] [PATCH] qemu: Fix crash on failed VM startup

On 06/01/2010 01:10 PM, Cole Robinson wrote:
> If VM startup fails early enough (can't find a referenced USB device),
> libvirtd will crash trying to clear the VNC port bit, since port = 0,
> which overflows us out of the bitmap bounds.
> Fix this by being more defensive in the bitmap operations, and only
> clearing a previously set VNC port.
> +++ b/src/util/bitmap.c
> @@ -118,7 +118,7 @@ int virBitmapSetBit(virBitmapPtr bitmap, size_t b)
>   */
>  int virBitmapClearBit(virBitmapPtr bitmap, size_t b)
>  {
> -    if (b > bitmap->size - 1)
> +    if (bitmap->size != 0 && b > bitmap->size - 1)

I think this could use a v2: virBitmapSetBit and virBitmapGetBit should
get the same treatment for bounds checking.

Meanwhile, we already reject attempts to create a bitmap with SIZE_MAX
bits.  Therefore, since b is unsigned, we can safely avoid the && and
instead do the computation via a single comparison:

if (bitmap->size <= b)
    return -1;

For that matter, should virBitmapAlloc(0) return NULL, instead of it's
current behavior of allocating an (empty) bitmap?

Eric Blake   eblake redhat com    +1-801-349-2682
Libvirt virtualization library http://libvirt.org

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