From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dan Carpenter Subject: Re: [PATCH] Ceph: Fix a use-after-free bug in ceph_destroy_client(). Date: Sun, 26 Dec 2010 01:46:58 +0300 Message-ID: <20101225224658.GC19019@bicker> References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: richard -rw- weinberger , ceph-devel@vger.kernel.org, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, Sage Weil , "David S. Miller" To: Jesper Juhl Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Sat, Dec 25, 2010 at 10:24:57PM +0100, Jesper Juhl wrote: > On Sat, 25 Dec 2010, richard -rw- weinberger wrote: > > > On Sat, Dec 25, 2010 at 7:17 PM, Jesper Juhl wrote: > > > Hello, > > > > > > In net/ceph/ceph_common.c::ceph_destroy_client() the pointer 'client' is > > > freed by kfree() and subsequently used in a call to dout() - use after > > > free bug. > > > > Not really. %p reads only the address of "client". > > kfree() does not alter this address. > > > > Ok, I see your point and you are correct. But still, the patch does not > change behaviour and it makes it absolutely clear that there's no > use-after-free bug, so it might still have merit... or? > I see these with Smatch as well. This type of usage is quite common. People do it deliberately and I guess they feel it's readable. Don't change them. If it were something that a static checker couldn't figure out, then I'd say change it, but really the static checkers should just be made smarter. Some day I'm going to make Smatch complain if it's a %s in the string instead of a %p, but for now I just ignore the false positives. regards, dan carpenter