Re: [PATCH] Typecasting required for comparing unlike datatypes

[Harsh Bora <harsh@linux.vnet.ibm.com>]

Hi Al,
Any comments?

On 12/08/2010 06:25 PM, Harsh Prateek Bora wrote:
> The existing code causes the if condition to pass when it should fail
> on a *64-bit kernel* because of implicit data type conversions. It can
> be observed by passing pos = -1 and count = some positive number.
> This results in function returning EOVERFLOW instead of EINVAL.
>
> With this patch, the function returns EINVAL when pos is -1 and count
> is a positive number. This can be tested by calling sendfile with
> offset = -1 and count = some positive number on a 64-bit kernel.
>
> Signed-off-by: Harsh Prateek Bora<harsh@linux.vnet.ibm.com>
> ---
>   fs/read_write.c |    2 +-
>   1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/fs/read_write.c b/fs/read_write.c
> index 431a0ed..a8eabd4 100644
> --- a/fs/read_write.c
> +++ b/fs/read_write.c
> @@ -38,7 +38,7 @@ __negative_fpos_check(struct file *file, loff_t pos, size_t count)
>   	 * pos or pos+count is negative here, check overflow.
>   	 * too big "count" will be caught in rw_verify_area().
>   	 */
> -	if ((pos<  0)&&  (pos + count<  pos))
> +	if ((pos<  0)&&  ( (loff_t) (pos + count)<  pos))
>   		return -EOVERFLOW;
>   	if (file->f_mode&  FMODE_UNSIGNED_OFFSET)
>   		return 0;