linux-kernel - Re: [patch v2] fcntl: return -EFAULT if copy_to

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Message-ID: <20100603131031.GM6822@laptop>
Date:	Thu, 3 Jun 2010 23:10:31 +1000
From:	Nick Piggin <npiggin@...e.de>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Takuya Yoshikawa <yoshikawa.takuya@....ntt.co.jp>,
	Jens Axboe <jaxboe@...ionio.com>,
	Dan Carpenter <error27@...il.com>,
	Matthew Wilcox <matthew@....cx>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [patch v2] fcntl: return -EFAULT if copy_to_user fails

On Thu, Jun 03, 2010 at 02:38:03PM +0200, Eric Dumazet wrote:
> Le jeudi 03 juin 2010 à 21:16 +0900, Takuya Yoshikawa a écrit :
> > (2010/06/03 20:59), Jens Axboe wrote:
> > > On 2010-06-03 12:35, Dan Carpenter wrote:
> > >> copy_to_user() returns the number of bytes remaining, but we want to
> > >> return -EFAULT.
> > >> 	ret = fcntl(fd, F_SETOWN_EX, NULL);
> > >> With the original code ret would be 8 here.
> > >>
> > >> V2: Takuya Yoshikawa pointed out a similar issue in f_getown_ex()
> > >
> > > Pretty basic bug, how long has this been there?
> > 
> > IIUC, from the beginning, when these were introduced.
> 
> Maybe copy_to_user() was changed sometime to return a partial count
> instead of EFAULT ?

I think it's been like that since first introduced. Some functions
do need to know in order to do partial copies.

 
> I do think we should have a set of helper functions, instead of
> spreading special EFAULT cases in one housand places...
> 
> This is really ugly.
> 
> static inline int sec_copy_to_user(arg1, arg2, arg3)
> {
> 	int res = copy_to_user(arg1, arg2, arg3);
> 
> 	return (res > 0) ? -EFAULT : res;
> }

It would be unfortunate if it adds more confusion. I'd prefer to have
a sufficiently different name. memcpy_to_user/memcpy_from_user
perhaps?

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