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



On 06/01/2010 04:03 PM, Eric Blake wrote:
> 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?
> 

Thanks, simplified that check and applied it to the other bitmap
functions. Updated patch sent.

- Cole


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