linux-kernel - Re: [PATCH -next 1/1] iomap: Fix a false positive of UBSAN in iomap_seek

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Date:   Sun, 4 Jul 2021 14:51:45 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Zhen Lei <thunder.leizhen@...wei.com>,
        "Darrick J . Wong" <djwong@...nel.org>,
        linux-xfs <linux-xfs@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -next 1/1] iomap: Fix a false positive of UBSAN in
 iomap_seek_data()

On Fri, Jul 02, 2021 at 10:34:23AM +0100, Christoph Hellwig wrote:
> We might as well just kill off the length variable while we're at it:

Acked-by: Matthew Wilcox (Oracle) <willy@...radead.org>

> diff --git a/fs/iomap/seek.c b/fs/iomap/seek.c
> index dab1b02eba5b7f..942e354e9e13e6 100644
> --- a/fs/iomap/seek.c
> +++ b/fs/iomap/seek.c
> @@ -35,23 +35,21 @@ loff_t
>  iomap_seek_hole(struct inode *inode, loff_t offset, const struct iomap_ops *ops)
>  {
>  	loff_t size = i_size_read(inode);
> -	loff_t length = size - offset;
>  	loff_t ret;
>  
>  	/* Nothing to be found before or beyond the end of the file. */
>  	if (offset < 0 || offset >= size)
>  		return -ENXIO;
>  
> -	while (length > 0) {
> -		ret = iomap_apply(inode, offset, length, IOMAP_REPORT, ops,
> -				  &offset, iomap_seek_hole_actor);
> +	while (offset < size) {
> +		ret = iomap_apply(inode, offset, size - offset, IOMAP_REPORT,
> +				  ops, &offset, iomap_seek_hole_actor);
>  		if (ret < 0)
>  			return ret;
>  		if (ret == 0)
>  			break;
>  
>  		offset += ret;
> -		length -= ret;
>  	}
>  
>  	return offset;