Re: [Cluster-devel] [BUG] fs: gfs2: possible null-pointer dereferences in gfs2_rgrp_bh_get()

From: Steven Whitehouse
Date: Wed Jul 24 2019 - 05:05:02 EST


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:
ÂÂÂ 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:
ÂÂÂ gfs2_rgrp_ondisk2lvb(..., rgd->rd_bits[0].bi_bh->b_data);
and on line 1228:
ÂÂÂ if (!gfs2_rgrp_lvb_valid(rgd))

Note that in gfs2_rgrp_lvb_valid(rgd), there is a statement on line 1114:
ÂÂÂ 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,