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

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Message-Id: <20071107190714.9c404e28.akpm@linux-foundation.org>
Date:	Wed, 7 Nov 2007 19:07:14 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Paul Mackerras <paulus@...ba.org>
Cc:	lkml@...idb.org, linux-kernel@...r.kernel.org, drepper@...hat.com,
	mtk-manpages@....net
Subject: Re: compat_sys_times() bogus until jiffies >= 0.

> 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.
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