Re: [PATCH 1/2] kernel/sys.c: return the current gid when error occurs

From: Chen Gang
Date: Wed Aug 07 2013 - 21:49:14 EST

On 08/08/2013 09:35 AM, Andy Lutomirski wrote:
> On Wed, Aug 7, 2013 at 6:30 PM, Chen Gang <gang.chen@xxxxxxxxxxx> wrote:
>> On 08/08/2013 12:58 AM, Andy Lutomirski wrote:
>>> On Wed, Aug 7, 2013 at 9:21 AM, Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
>>>> On 08/06, Andy Lutomirski wrote:
>>>>> I assume that what the man page means is that the return value is
>>>>> whatever fsgid was prior to the call. On error, fsgid isn't changed, so
>>>>> the return value is still "current".
>>>> Probably... Still
>>>> On success, the previous value of fsuid is returned.
>>>> On error, the current value of fsuid is returned.
>>>> looks confusing. sys_setfsuid() always returns the old value.
>>>>> (FWIW, this behavior is awful and is probably the cause of a security
>>>>> bug or three, since success and failure are indistinguishable.
>>>> At least this all looks strange.
>>>> I dunno if we can change this old behaviour. I won't be surprized
>>>> if someone already uses setfsuid(-1) as getfsuid().
>> Oh, really it is.
>> Hmm... as a pair function, we need add getfsuid() too, if we do not add
>> it, it will make negative effect with setfsuid().
>> Since it is a system call, we have to keep compitable.
>> So in my opinion, better add getfsuid2()/setfsuid2() instead of current
>> setfsuid()
> How about getfsuid() and setfsuid2()?

Hmm... I have 2 reasons, please check.

1st reason: I checked history (just like Kees Cook suggested),
getfsuid() is mentioned before (you can google to find it), so need use
getfsuid2() to bypass the history complex.

And 2nd reason: getfsuid() seems more like the pair of setfsuid(), not
for setfsuid2().

> --Andy

Chen Gang
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at