Re: [PATCH 1/2] fibmap: Warn and return an error in case of block > INT_MAX

[Eric Biggers <ebiggers@kernel.org>]

On Fri, Apr 24, 2020 at 12:52:17PM +0530, Ritesh Harjani wrote:
> We better warn the fibmap user and not return a truncated and therefore
> an incorrect block map address if the bmap() returned block address
> is greater than INT_MAX (since user supplied integer pointer).
> 
> It's better to WARN all user of ioctl_fibmap() and return a proper error
> code rather than silently letting a FS corruption happen if the user tries
> to fiddle around with the returned block map address.
> 
> We fix this by returning an error code of -ERANGE and returning 0 as the
> block mapping address in case if it is > INT_MAX.
> 
> Signed-off-by: Ritesh Harjani <riteshh@linux.ibm.com>
> ---
>  fs/ioctl.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/fs/ioctl.c b/fs/ioctl.c
> index f1d93263186c..3489f3a12c1d 100644
> --- a/fs/ioctl.c
> +++ b/fs/ioctl.c
> @@ -71,6 +71,11 @@ static int ioctl_fibmap(struct file *filp, int __user *p)
>  	block = ur_block;
>  	error = bmap(inode, &block);
>  
> +	if (block > INT_MAX) {
> +		error = -ERANGE;
> +		WARN(1, "would truncate fibmap result\n");
> +	}
> +

WARN() is only for kernel bugs.  This case would be a userspace bug, not a
kernel bug, right?  If so, it should use pr_warn(), not WARN().

- Eric