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

Hi,

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

Signed-off-by Bob Peterson <[email protected]>

---

fs/gfs2/rgrp.c +8 -4

index 5bd2169..960aaf4 100644
@@ -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;
  }