Re: [Xenomai-core] [PATCH] posix: Fix error checks when copying user strings

[Jan Kiszka <jan.kiszka@domain.hid>]

Jan Kiszka wrote:
> Gilles Chanteperdrix wrote:
>> Jan Kiszka wrote:
>>> Gilles Chanteperdrix wrote:
>>>> Jan Kiszka wrote:
>>>>> Gilles Chanteperdrix wrote:
>>>>>> Jan Kiszka wrote:
>>>>>>> Obviously a conversion error while switching to __xn_safe*.
>>>>>>>
>>>>>>> Signed-off-by: Jan Kiszka <jan.kiszka@domain.hid>
>>>>>> Well, I have just checked the kernel code, and 0 as a return value of
>>>>>> strncpy_from_user is treated as a value in most places, even if not -EFAULT.
>>>>>>
>>>>> Better check our code: :) __xn_safe_strncpy_from_user works differently.
>>>> Then I would tend to consider that xn_safe_strncpy is broken.
>>> No, because it not a derivate of strncpy_from_user, but an internal
>>> service optimized for the most common use cases (where you don't care
>>> about the precise return value).
>> So, what should I call if I care about the return value ?
> 
> The old combo of access_rok() and __xn_strncpy_from_user() - ah, I see
> the issue: POSIX requires the length to report overflows to the users.
> Hmm, then back to the old code, just adding the missing address range check.
> 

Forget that, now I should have looked into our code: The "safe" version
transparently calls __xn_strncpy_from_user, no need to go by foot here.

Jan

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