linux-kernel - Re: [PATCH] dup2: Fix return value with oldfd == newfd and invalid fd

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Message-ID: <4A0875E5.9080005@suse.com>
Date:	Mon, 11 May 2009 15:00:53 -0400
From:	Jeff Mahoney <jeffm@...e.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Al Viro <viro@....linux.org.uk>
Subject: Re: [PATCH] dup2: Fix return value with oldfd == newfd and invalid
 fd

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Linus Torvalds wrote:
> 
> On Mon, 11 May 2009, Jeff Mahoney wrote:
>>  The return value of dup2 when oldfd == newfd and the fd isn't valid is not
>>  getting properly sign extended. We end up with 4294967287 instead of -EBADF.
> 
> Indeed.
> 
>>  This patch uses a signed int for the error value so it is properly extended.
> 
> However, I'd rather move the new variable into the block where it is used, 
> and keep the whole corner-case thing self-contained.
> 
> So can you verify that this trivial variation on the patch is ok by you, 
> and I'll commit it as yours with your message? (I realize it's really 
> trivial, and I could just do this myself, but good to get the change 
> ack'ed anyway).

Oh, of course. That's fine with me.

- -Jeff

> 
> 		Linus
> 
> ---
>  fs/fcntl.c |    6 ++++--
>  1 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/fcntl.c b/fs/fcntl.c
> index cc8e4de..1ad7031 100644
> --- a/fs/fcntl.c
> +++ b/fs/fcntl.c
> @@ -117,11 +117,13 @@ SYSCALL_DEFINE2(dup2, unsigned int, oldfd, unsigned int, newfd)
>  {
>  	if (unlikely(newfd == oldfd)) { /* corner case */
>  		struct files_struct *files = current->files;
> +		int retval = oldfd;
> +
>  		rcu_read_lock();
>  		if (!fcheck_files(files, oldfd))
> -			oldfd = -EBADF;
> +			retval = -EBADF;
>  		rcu_read_unlock();
> -		return oldfd;
> +		return retval;
>  	}
>  	return sys_dup3(oldfd, newfd, 0);
>  }


- --
Jeff Mahoney
SUSE Labs
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