Re: [Xen-devel] [PATCH] console: avoid buffer overflow in guest_console_write()

[Jan Beulich <jbeulich@xxxxxxxx>]

On 29.11.2019 13:15, Andrew Cooper wrote:
> On 29/11/2019 12:13, Jan Beulich wrote:
>> On 29.11.2019 13:01, Ian Jackson wrote:
>>> Jan Beulich writes ("Re: [PATCH] console: avoid buffer overflow in 
>>> guest_console_write()"):
>>>> On 29.11.2019 11:22, Andrew Cooper wrote:
>>>>> Is sizeof(array[0]) always 0, or is this just a GCC-ism ?  Godbolt
>>>>> suggests is 0 on all compiler we support.
>>>>>
>>>>> Either way, isn't the more common idiom + 0ul ?  Personally, I feel that
>>>>> is clearer to follow.
>>>> I decided against + 0ul or alike because in principle size_t
>>>> and unsigned long are different types. In particular 32-bit
>>>> x86 gcc uses unsigned int for size_t, and hence min()'s
>>>> type safety check would cause the build to fail there. The
>>>> same risk obviously exists for any 32-bit arch (e.g. Arm32,
>>>> but I haven't checked what type it actually uses).
>>> I don't know what i wrong with
>>>    (size_t)0
>>> which is shorter, even !
>> True. Yet it contains a cast, no matter how risk-free it may be
>> in this case. With a cast, I could as well have written (yet
>> shorter) (size_t)count.
> 
> Given that min() has a very strict typecheck, I think we should permit
> any use of an explicit cast in a single operand, because it *is* safer
> than switching to the min_t() route to make things compile.

Well, I can switch to (size_t)count if this is liked better
overall.

Jan

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