linux-kernel - Re: [PATCH] init/do_mounts.c: Harden split_fs

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Date:   Thu, 16 Sep 2021 07:39:10 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     Vivek Goyal <vgoyal@...hat.com>
Cc:     viro@...iv.linux.org.uk,
        Linux fsdevel mailing list <linux-fsdevel@...r.kernel.org>,
        linux kernel mailing list <linux-kernel@...r.kernel.org>,
        Jan Kara <jack@...e.cz>, xu.xin16@....com.cn,
        Christoph Hellwig <hch@...radead.org>, zhang.yunkai@....com.cn
Subject: Re: [PATCH] init/do_mounts.c: Harden split_fs_names() against buffer
 overflow

On Wed, Sep 15, 2021 at 11:22:04AM -0400, Vivek Goyal wrote:
> Will be nice to pass size of input buffer to split_fs_names() and
> put enough checks in place so such buffer overrun possibilities
> do not occur.

Will be nice sounds weird.

> 
> Hence this patch adds "size" parameter to split_fs_names() and makes
> sure we do not access memory beyond size. If input string "names"
> is larger than passed in buffer, input string will be truncated to
> fit in buffer.

There's really two aspects here:  checking for a max size and explicitly
passing one.  I'm fine with passing the argument even if it always is
PAGE_SIZE, but this should probably be documented a little better.

Otherwise looks good:

Reviewed-by: Christoph Hellwig <hch@....de>