From mboxrd@z Thu Jan 1 00:00:00 1970 From: Steven Whitehouse Date: Fri, 10 Jun 2016 11:31:33 +0100 Subject: [Cluster-devel] [GFS2 PATCH] GFS2: don't set rgrp gl_object until it's inserted into rgrp tree In-Reply-To: <881894074.17586850.1465504077063.JavaMail.zimbra@redhat.com> References: <881894074.17586850.1465504077063.JavaMail.zimbra@redhat.com> Message-ID: <575A9705.5010705@redhat.com> List-Id: To: cluster-devel.redhat.com MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Hi, Acked-by: Steven Whitehouse Steve. On 09/06/16 21:27, Bob Peterson wrote: > 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 > --- > diff --git a/fs/gfs2/rgrp.c b/fs/gfs2/rgrp.c > index 5bd2169..960aaf4 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; > } >