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

From: Jia-Ju Bai
Date: Wed Jul 24 2019 - 04:50:06 EST

In gfs2_rgrp_bh_get, there is an if statement on line 1191 to check whether "rgd->rd_bits[0].bi_bh" is NULL.
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);
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