linux-ext4 - Re: [PATCH 1/2] fibmap: Warn and return an error in case of block > INT

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Date:   Fri, 24 Apr 2020 12:17:39 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     Ritesh Harjani <riteshh@...ux.ibm.com>
Cc:     linux-fsdevel@...r.kernel.org, linux-xfs@...r.kernel.org,
        Alexander Viro <viro@...iv.linux.org.uk>,
        "Darrick J . Wong" <darrick.wong@...cle.com>,
        Christoph Hellwig <hch@...radead.org>,
        Jan Kara <jack@...e.com>, tytso@....edu,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
        linux-ext4@...r.kernel.org
Subject: Re: [PATCH 1/2] fibmap: Warn and return an error in case of block >
 INT_MAX

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@...ux.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