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Re: [patch] Fix for heap overflow in wscanf (BZ 16618)

On 02/03/2015 01:01 PM, Rich Felker wrote:
> On Tue, Feb 03, 2015 at 11:24:08AM -0500, Carlos O'Donell wrote:
>> On 02/02/2015 01:59 PM, Paul Pluzhnikov wrote:
>>> On Mon, Feb 2, 2015 at 10:45 AM, Andreas Schwab <> wrote:
>>>                  \
>>>>> +               __set_errno (ENOMEM);                                     \
>>>> You already have a meaningful errno from the failed realloc.
>>> I see. And we are sure that "free(old)" will not touch errno?
>> Yes, free can never fail. If free were to touch errno it would be a bug,
>> or would only happen in cases of undefined behaviour.
> free can make a syscall that will set errno unless you suppress this
> behavior -- munmap can fail due to inability to split an existing vma
> due to hitting the vma limit or simply a kernel oom condition. In this
> case I suspect you get the result you want, ENOMEM, anyway, but in
> general if you want free to have a contract not to set errno, that
> requires some attention, and it's almost surely not satisfied if
> applications are allowed to replace free...

I would consider all of these things bugs and particularly in the use
case of the user-provide free() a conformance issue for modifying errno
without there being an error.


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