From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from userp2130.oracle.com ([156.151.31.86]:49548 "EHLO userp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726197AbfG2O6s (ORCPT ); Mon, 29 Jul 2019 10:58:48 -0400 Date: Mon, 29 Jul 2019 07:58:38 -0700 From: "Darrick J. Wong" Subject: Re: [PATCH] fs: xfs: Fix possible null-pointer dereferences in xchk_da_btree_block_check_sibling() Message-ID: <20190729145838.GN1561054@magnolia> References: <20190729032401.28081-1-baijiaju1990@gmail.com> <20190729042034.GM1561054@magnolia> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Sender: linux-xfs-owner@vger.kernel.org List-ID: List-Id: xfs To: Jia-Ju Bai Cc: bfoster@redhat.com, sandeen@sandeen.net, linux-xfs@vger.kernel.org, linux-kernel@vger.kernel.org On Mon, Jul 29, 2019 at 03:25:04PM +0800, Jia-Ju Bai wrote: > > > On 2019/7/29 12:20, Darrick J. Wong wrote: > > On Mon, Jul 29, 2019 at 11:24:01AM +0800, Jia-Ju Bai wrote: > > > In xchk_da_btree_block_check_sibling(), there is an if statement on > > > line 274 to check whether ds->state->altpath.blk[level].bp is NULL: > > > if (ds->state->altpath.blk[level].bp) > > > > > > When ds->state->altpath.blk[level].bp is NULL, it is used on line 281: > > > xfs_trans_brelse(..., ds->state->altpath.blk[level].bp); > > > struct xfs_buf_log_item *bip = bp->b_log_item; > > > ASSERT(bp->b_transp == tp); > > > > > > Thus, possible null-pointer dereferences may occur. > > > > > > To fix these bugs, ds->state->altpath.blk[level].bp is checked before > > > being used. > > > > > > These bugs are found by a static analysis tool STCheck written by us. > > > > > > Signed-off-by: Jia-Ju Bai > > > --- > > > fs/xfs/scrub/dabtree.c | 4 +++- > > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > > > diff --git a/fs/xfs/scrub/dabtree.c b/fs/xfs/scrub/dabtree.c > > > index 94c4f1de1922..33ff90c0dd70 100644 > > > --- a/fs/xfs/scrub/dabtree.c > > > +++ b/fs/xfs/scrub/dabtree.c > > > @@ -278,7 +278,9 @@ xchk_da_btree_block_check_sibling( > > > /* Compare upper level pointer to sibling pointer. */ > > > if (ds->state->altpath.blk[level].blkno != sibling) > > > xchk_da_set_corrupt(ds, level); > > > - xfs_trans_brelse(ds->dargs.trans, ds->state->altpath.blk[level].bp); > > > + if (ds->state->altpath.blk[level].bp) > > > + xfs_trans_brelse(ds->dargs.trans, > > > + ds->state->altpath.blk[level].bp); > > Indentation here (in xfs we use two spaces) > > Okay, I will fix this. > > > > > Also, uh, shouldn't we set ds->state->altpath.blk[level].bp to NULL > > since we've released the buffer? > > So I should set ds->state->altpath.blk[level].bp to NULL at the end of the > function xchk_da_btree_block_check_sibling()? > Like: >     if (ds->state->altpath.blk[level].bp) >         xfs_trans_brelse(ds->dargs.trans, >                 ds->state->altpath.blk[level].bp); >     ds->state->altpath.blk[level].bp = NULL; You could put the whole thing in a single if clause, e.g. if (ds->state->altpath.blk[level].bp) { xfs_trans_brelse(ds->dargs.trans, ds->state->altpath.blk[level].bp); ds->state->altpath.blk[level].bp = NULL; } --D > > > Best wishes, > Jia-Ju Bai