linux-kernel - Re: [PATCH] mm: adjust max read count in generic_file_buffered

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Message-ID: <20180806102203.hmobd26cujmlfcsw@quack2.suse.cz>
Date:   Mon, 6 Aug 2018 12:22:03 +0200
From:   Jan Kara <jack@...e.cz>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Jan Kara <jack@...e.cz>, Chengguang Xu <cgxu519@....com>,
        mgorman@...hsingularity.net, jlayton@...hat.com,
        ak@...ux.intel.com, mawilcox@...rosoft.com,
        tim.c.chen@...ux.intel.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Al Viro <viro@...IV.linux.org.uk>
Subject: Re: [PATCH] mm: adjust max read count in generic_file_buffered_read()

On Fri 20-07-18 16:14:29, Andrew Morton wrote:
> On Thu, 19 Jul 2018 10:58:12 +0200 Jan Kara <jack@...e.cz> wrote:
> 
> > On Thu 19-07-18 16:17:26, Chengguang Xu wrote:
> > > When we try to truncate read count in generic_file_buffered_read(),
> > > should deliver (sb->s_maxbytes - offset) as maximum count not
> > > sb->s_maxbytes itself.
> > > 
> > > Signed-off-by: Chengguang Xu <cgxu519@....com>
> > 
> > Looks good to me. You can add:
> > 
> > Reviewed-by: Jan Kara <jack@...e.cz>
> 
> Yup.
> 
> What are the runtime effects of this bug?

Good question. I think ->readpage() could be called for index beyond
maximum file size supported by the filesystem leading to weird filesystem
behavior due to overflows in internal calculations.

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR