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

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>

1 files changed, 8 insertions, 4 deletions

diff --git a/fs/gfs2/rgrp.c b/fs/gfs2/rgrp.c
index 5bd216901e89..960aaf43d665 100644
--- a/fs/gfs2/rgrp.c
+++ b/fs/gfs2/rgrp.c
@@ -722,6 +722,7 @@ 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);
         }
@@ -916,9 +917,6 @@ 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_MASK;
-        rgd->rd_gl->gl_vm.end = PAGE_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)
@@ -926,14 +924,20 @@ 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;
 }