linux-kernel - Re: compat_sys_times() bogus until jiffies >= 0.

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Message-Id: <200711081927.19394.vda.linux@googlemail.com>
Date:	Thu, 8 Nov 2007 19:27:19 +0000
From:	Denys Vlasenko <vda.linux@...glemail.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Paul Mackerras <paulus@...ba.org>, lkml@...idb.org,
	linux-kernel@...r.kernel.org, drepper@...hat.com,
	mtk-manpages@....net
Subject: Re: compat_sys_times() bogus until jiffies >= 0.

On Thursday 08 November 2007 03:07, Andrew Morton wrote:
> > On Thu, 8 Nov 2007 12:53:57 +1100 Paul Mackerras <paulus@...ba.org> wrote:
> > Andrew Morton writes:
> > 
> > > Given all this stuff, the return value from sys_times() doesn't seem a
> > > particularly useful or reliable kernel interface.
> > 
> > I think the best thing would be to ignore any error from copy_to_user
> > and always return the number of clock ticks.  We should call
> > force_successful_syscall_return, and glibc on x86 should be taught not
> > to interpret negative values as an error.
> 
> Changing glibc might be hard ;)
> 
> > POSIX doesn't require us to return an EFAULT error if the buf argument
> > is bogus.  If userspace does supply a bogus buf pointer, then either
> > it will dereference it itself and get a segfault, or it won't
> > dereference it, in which case it obviously didn't care about the
> > values we tried to put there.
> > 
> > If we try to return an error under some circumstances, then there is
> > at least one 32-bit value for the number of ticks that will cause
> > confusion.  We can either change that value (or values) to some other
> > value, which seems pretty bogus, or we can just decide not to return
> > any errors.  The latter seems to me to have no significant downside
> > and to be the simplest solution to the problem.
> 
> "the latter" is what my protopatch does isn't it?  It wraps at 0x7fffffff.
> It appears that glibc treats all of 0x80000000-0xffffffff as an error.

The best solution is to change the kernel to never return an error
and to change glibc to never treat return as an error.
--
vda
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