linux-kernel - Re: [PATCH v2] vfs: read file_handle only once in handle_to

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Message-ID: <55424464.9030906@oracle.com>
Date:	Thu, 30 Apr 2015 11:04:04 -0400
From:	Sasha Levin <sasha.levin@...cle.com>
To:	linux-kernel@...r.kernel.org
CC:	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v2] vfs: read file_handle only once in handle_to_path

ping?

On 01/28/2015 03:30 PM, Sasha Levin wrote:
> We used to read file_handle twice. Once to get the amount of extra bytes, and
> once to fetch the entire structure.
> 
> This may be problematic since we do size verifications only after the first
> read, so if the number of extra bytes changes in userspace between the first
> and second calls, we'll have an incoherent view of file_handle.
> 
> Instead, read the constant size once, and copy that over to the final
> structure without having to re-read it again.
> 
> Signed-off-by: Sasha Levin <sasha.levin@...cle.com>
> ---
> Change in v2:
>  - Use the f_handle pointer rather than size of struct
> 
>  fs/fhandle.c |    5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/fhandle.c b/fs/fhandle.c
> index 999ff5c..d59712d 100644
> --- a/fs/fhandle.c
> +++ b/fs/fhandle.c
> @@ -195,8 +195,9 @@ static int handle_to_path(int mountdirfd, struct file_handle __user *ufh,
>  		goto out_err;
>  	}
>  	/* copy the full handle */
> -	if (copy_from_user(handle, ufh,
> -			   sizeof(struct file_handle) +
> +	*handle = f_handle;
> +	if (copy_from_user(&handle->f_handle,
> +			   &ufh->f_handle,
>  			   f_handle.handle_bytes)) {
>  		retval = -EFAULT;
>  		goto out_handle;
> 

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