linux-kernel - Re: [Cluster-devel] [BUG] fs: gfs2: possible null-pointer dereferences in gfs2_rgrp_bh

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Message-ID: <cd7c0bb4-53d2-8a67-0719-c26d043a31fc@redhat.com>
Date:   Wed, 24 Jul 2019 10:04:55 +0100
From:   Steven Whitehouse <swhiteho@...hat.com>
To:     Jia-Ju Bai <baijiaju1990@...il.com>, rpeterso@...hat.com,
        agruenba@...hat.com
Cc:     cluster-devel@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [Cluster-devel] [BUG] fs: gfs2: possible null-pointer
 dereferences in gfs2_rgrp_bh_get()

Hi,

On 24/07/2019 09:50, Jia-Ju Bai wrote:
> In gfs2_rgrp_bh_get, there is an if statement on line 1191 to check 
> whether "rgd->rd_bits[0].bi_bh" is NULL.

That is how we detect whether the rgrp has already been read in, so the 
function is skipped in the case that we've already read in the rgrp.


> When "rgd->rd_bits[0].bi_bh" is NULL, it is used on line 1216:
>     gfs2_rgrp_in(rgd, (rgd->rd_bits[0].bi_bh)->b_data);

No it isn't. See line 1196 where bi_bh is set, and where we also bail 
out (line 1198) in case it has not been set.


> and on line 1225:
>     gfs2_rgrp_ondisk2lvb(..., rgd->rd_bits[0].bi_bh->b_data);
> and on line 1228:
>     if (!gfs2_rgrp_lvb_valid(rgd))
>
> Note that in gfs2_rgrp_lvb_valid(rgd), there is a statement on line 1114:
>     struct gfs2_rgrp *str = (struct gfs2_rgrp 
> *)rgd->rd_bits[0].bi_bh->b_data;
>
> Thus, possible null-pointer dereferences may occur.
>
> These bugs are found by a static analysis tool STCheck written by us.
> I do not know how to correctly fix these bugs, so I only report bugs.
>
>
> Best wishes,
> Jia-Ju Bai
>
So I'm not seeing how there can be a NULL deref in those later lines. I 
think this is another false positive,

Steve.