Date: Thu, 3 Jun 2010 23:10:31 +1000
From: Nick Piggin <npiggin@suse.de>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>,
       Jens Axboe <jaxboe@fusionio.com>, Dan Carpenter <error27@gmail.com>,
       Matthew Wilcox <matthew@wil.cx>,
       Alexander Viro <viro@zeniv.linux.org.uk>,
       Andrew Morton <akpm@linux-foundation.org>,
       Oleg Nesterov <oleg@redhat.com>, Greg Kroah-Hartman <gregkh@suse.de>,
       Peter Zijlstra <a.p.zijlstra@chello.nl>, linux-fsdevel@vger.kernel.org,
       linux-kernel@vger.kernel.org
Subject: Re: [patch v2] fcntl: return -EFAULT if copy_to_user fails
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On Thu, Jun 03, 2010 at 02:38:03PM +0200, Eric Dumazet wrote:
> Le jeudi 03 juin 2010 ? 21:16 +0900, Takuya Yoshikawa a ?crit :
> > (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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