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Date:   Wed, 15 Nov 2023 14:39:17 -0800
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Edward Adam Davis <eadavis@qq.com>
Cc:     syzbot+604424eb051c2f696163@syzkaller.appspotmail.com,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        phillip@squashfs.org.uk, squashfs-devel@lists.sourceforge.net,
        syzkaller-bugs@googlegroups.com
Subject: Re: [PATCH] squashfs: fix oob in squashfs_readahead
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On Wed, 15 Nov 2023 12:05:35 +0800 Edward Adam Davis <eadavis@qq.com> wrote:

> Before performing a read ahead operation in squashfs_read_folio() and 
> squashfs_readahead(), check if i_size is not 0 before continuing.

I'll merge this for testing, pending Phillip's review.  One thing:

> --- a/fs/squashfs/block.c
> +++ b/fs/squashfs/block.c
> @@ -323,7 +323,7 @@ int squashfs_read_data(struct super_block *sb, u64 index, int length,
>  	}
>  	if (length < 0 || length > output->length ||
>  			(index + length) > msblk->bytes_used) {
> -		res = -EIO;
> +		res = length < 0 ? -EIO : -EFBIG;
>  		goto out;
>  	}

Seems a bit ugly to test `length' twice for the same thing.  How about

	if (length < 0) {
		res = -EIO;
		got out;
	}
	if (length > output->length || (index + length) > msblk->bytes_used) {
		res = -EFBIG;
		goto out;
	}

?