GFS2: don't set rgrp gl_object until it's inserted into rgrp tree

commit 36e4ad0316c017d5b271378ed9a1c9a4b77fab5f upstream.

Before this patch, function read_rindex_entry would set a rgrp
glock's gl_object pointer to itself before inserting the rgrp into
the rgrp rbtree. The problem is: if another process was also reading
the rgrp in, and had already inserted its newly created rgrp, then
the second call to read_rindex_entry would overwrite that value,
then return a bad return code to the caller. Later, other functions
would reference the now-freed rgrp memory by way of gl_object.
In some cases, that could result in gfs2_rgrp_brelse being called
twice for the same rgrp: once for the failed attempt and once for
the "real" rgrp release. Eventually the kernel would panic.
There are also a number of other things that could go wrong when
a kernel module is accessing freed storage. For example, this could
result in rgrp corruption because the fake rgrp would point to a
fake bitmap in memory too, causing gfs2_inplace_reserve to search
some random memory for free blocks, and find some, since we were
never setting rgd->rd_bits to NULL before freeing it.

This patch fixes the problem by not setting gl_object until we
have successfully inserted the rgrp into the rbtree. Also, it sets
rd_bits to NULL as it frees them, which will ensure any accidental
access to the wrong rgrp will result in a kernel panic rather than
file system corruption, which is preferred.

Signed-off-by: Bob Peterson <rpeterso@redhat.com>
[bwh: Backported to 4.4: adjust context]
Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/fs/gfs2/rgrp.c b/fs/gfs2/rgrp.c
index ef24894edecc1b0468ccf1bdc64cb7ce77bb0501..9c159e6ad11642f62b6ce7257dcf7a9b401ee2b8 100644 (file)
--- a/fs/gfs2/rgrp.c
+++ b/fs/gfs2/rgrp.c
@@ -739,6 +739,7 @@ void gfs2_clear_rgrpd(struct gfs2_sbd *sdp)
 
                gfs2_free_clones(rgd);
                kfree(rgd->rd_bits);
+               rgd->rd_bits = NULL;
                return_all_reservations(rgd);
                kmem_cache_free(gfs2_rgrpd_cachep, rgd);
        }
@@ -933,10 +934,6 @@ static int read_rindex_entry(struct gfs2_inode *ip)
        if (error)
                goto fail;
 
-       rgd->rd_gl->gl_object = rgd;
-       rgd->rd_gl->gl_vm.start = (rgd->rd_addr * bsize) & PAGE_CACHE_MASK;
-       rgd->rd_gl->gl_vm.end = PAGE_CACHE_ALIGN((rgd->rd_addr +
-                                                 rgd->rd_length) * bsize) - 1;
        rgd->rd_rgl = (struct gfs2_rgrp_lvb *)rgd->rd_gl->gl_lksb.sb_lvbptr;
        rgd->rd_flags &= ~(GFS2_RDF_UPTODATE | GFS2_RDF_PREFERRED);
        if (rgd->rd_data > sdp->sd_max_rg_data)
@@ -944,14 +941,20 @@ static int read_rindex_entry(struct gfs2_inode *ip)
        spin_lock(&sdp->sd_rindex_spin);
        error = rgd_insert(rgd);
        spin_unlock(&sdp->sd_rindex_spin);
-       if (!error)
+       if (!error) {
+               rgd->rd_gl->gl_object = rgd;
+               rgd->rd_gl->gl_vm.start = (rgd->rd_addr * bsize) & PAGE_MASK;
+               rgd->rd_gl->gl_vm.end = PAGE_ALIGN((rgd->rd_addr +
+                                                   rgd->rd_length) * bsize) - 1;
                return 0;
+       }
 
        error = 0; /* someone else read in the rgrp; free it and ignore it */
        gfs2_glock_put(rgd->rd_gl);
 
 fail:
        kfree(rgd->rd_bits);
+       rgd->rd_bits = NULL;
        kmem_cache_free(gfs2_rgrpd_cachep, rgd);
        return error;
 }