From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:46488) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dUX3h-0005O9-Vy for qemu-devel@nongnu.org; Mon, 10 Jul 2017 07:40:59 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dUX3e-0006Bd-18 for qemu-devel@nongnu.org; Mon, 10 Jul 2017 07:40:58 -0400 Date: Mon, 10 Jul 2017 13:40:48 +0200 From: Kevin Wolf Message-ID: <20170710114048.GC5772@noname.redhat.com> References: <1496857819-12466-1-git-send-email-kwolf@redhat.com> <1496857819-12466-6-git-send-email-kwolf@redhat.com> <20170613164628.GG4383@noname.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Subject: Re: [Qemu-devel] [PULL 5/8] commit: Fix use after free in completion List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Maydell Cc: Qemu-block , QEMU Developers Am 09.07.2017 um 19:09 hat Peter Maydell geschrieben: > On 13 June 2017 at 17:46, Kevin Wolf wrote: > > Am 13.06.2017 um 18:12 hat Peter Maydell geschrieben: > >> On 7 June 2017 at 18:50, Kevin Wolf wrote: > >> > diff --git a/block/commit.c b/block/commit.c > >> > index a3028b2..af6fa68 100644 > >> > --- a/block/commit.c > >> > +++ b/block/commit.c > >> > @@ -89,6 +89,10 @@ static void commit_complete(BlockJob *job, void *opaque) > >> > int ret = data->ret; > >> > bool remove_commit_top_bs = false; > >> > > >> > + /* Make sure overlay_bs and top stay around until bdrv_set_backing_hd() */ > >> > + bdrv_ref(top); > >> > + bdrv_ref(overlay_bs); > >> > + > >> > /* Remove base node parent that still uses BLK_PERM_WRITE/RESIZE before > >> > * the normal backing chain can be restored. */ > >> > blk_unref(s->base); > >> > >> Hi -- coverity complains about this change, because bdrv_ref() > >> assumes that its argument is not NULL, but later on in commit_complete() > >> we have a check > >> "if (overlay_bs && ...)" > >> which assumes its argument might be NULL. (CID 1376205) > >> > >> Which is correct? > > > > I saw the Coverity report and am looking into it. It's not completely > > clear to me yet which is correct, but I suspect it can be NULL. > > Just a nudge on this one -- I don't think there's been a patch sent > to the list for this check-after-use ? > > (It's one of just 7 coverity issues left which haven't had at least > a patch sent to the list now...) As far as I can tell, this can't currently be triggered. I intended to fix it with some work on the commit block job that I need to do anyway, and which would potentially enable a way to trigger it. But it turned out that this is a bit more complicated than I thought. So maybe I'd better just post a very small patch that silences Coverity (without making a practical difference) until I can finish the real thing. Kevin