linux-kernel - Re: [PATCH] kernel/itimer.c: for return value, using -EINVAL instead of -EFAULT

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Date:	Thu, 20 Jun 2013 09:44:05 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Chen Gang <gang.chen@...anux.com>
cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kernel/itimer.c: for return value, using -EINVAL instead
 of -EFAULT

On Thu, 20 Jun 2013, Chen Gang wrote:
> On 06/20/2013 02:59 PM, Thomas Gleixner wrote:
> > On Thu, 20 Jun 2013, Chen Gang wrote:
> > 
> >> > For the system call getitimer(), if the parameter 'value' is NULL, need
> >> > return -EINVAL, not -EFAULT.
> > Care to explain why? Because you are feeling so?
> > 
> 
> I am not feeling so, the original implementation really just checks the parameter 'value', if it is invalid, need return, is it incorrect ??
> 
> 
> > I recommend reading the man page of getitimer:
> > 
> >  ERRORS
> >        EFAULT new_value, old_value, or curr_value is not valid a pointer.
> > 
> > And NULL is definitely NOT a valid pointer.
> > 
> > The Posix spec does not specify an explicit error value for this
> > syscall, but the general policy is:
> > 
> > [EFAULT]
> >     Bad address. The system detected an invalid address in attempting
> >     to use an argument of a call. The reliable detection of this error
> >     cannot be guaranteed, and when not detected may result in the
> >     generation of a signal, indicating an address violation, which is
> >     sent to the process.
> > 
> > And we made use of this, which is correct and makes sense.
> > 
> > Returning EINVAL makes no sense at all, because EINVAL _IS_ a
> > specified error code for this syscall:
> > 
> > [EINVAL]
> >         The which argument is not recognized.
> 
> That means we need not check the parameter 'value' out side of copy_to_user().

We could do that, but that makes no sense. If we can detect it before
copy_to_user() we can return the exactly same return value which we
would return via copy_to_user(). That avoids to take a trap and run
through the fixup code.

Thanks,

	tglx

_
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