Received-SPF: pass (google.com: best guess record for domain of linux-wireless-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
References: <20191121224139.58281-1-briannorris@chromium.org> <e86eb7a3-95e1-f9e1-4ab9-aa38a4f4481e@phrozen.org>
In-Reply-To: <e86eb7a3-95e1-f9e1-4ab9-aa38a4f4481e@phrozen.org>
From:   Brian Norris <briannorris@chromium.org>
Date:   Thu, 21 Nov 2019 15:30:14 -0800
Message-ID: <CA+ASDXPZA5ObVJmhm11OQFP2ngeDZhsr_FAgxSz8P8QX+e7WEA@mail.gmail.com>
Subject: Re: [PATCH] iw: scan: fix double-free in error paths
To:     John Crispin <john@phrozen.org>
Cc:     Johannes Berg <johannes@sipsolutions.net>,
        linux-wireless <linux-wireless@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-wireless-owner@vger.kernel.org
Precedence: bulk

On Thu, Nov 21, 2019 at 3:24 PM John Crispin <john@phrozen.org> wrote:
>
> On 21/11/2019 23:41, Brian Norris wrote:
> > Hit when, for instance, I'm stupid enough to type an invalid scan
> > command:
> >
> >    # iw wlan0 scan -h
> >    BUG at file position lib/msg.c:572:void nlmsg_free(struct nl_msg *)
> >    iw: lib/msg.c:572: void nlmsg_free(struct nl_msg *): Assertion `0' failed.
> >    Aborted (core dumped)
> >
> > Fixes: 2f74c59cf11e ("iw: fix memory leaks inside handle_scan")
> > Cc: John Crispin <john@phrozen.org>
> wasn't me, nobody saw do anything
> try
> 367e7dd3 (Amit Khatri            2015-06-26 09:02:36 +0000  451)
>                 nlmsg_free(ssids);
> 367e7dd3 (Amit Khatri            2015-06-26 09:02:36 +0000  452)
>                 nlmsg_free(freqs);
> ???

I don't really care about "who", but it's nice to correctly note "what":

Your patch added 'goto nla_put_failure' in the DONE case (or
fallthrough from NONE), which introduced the double-free. Previously,
it was just a 'return', which meant we needed to do the cleanup in
'case DONE'.

For Amit's patch: note how there's a 'return', which makes his code
the only possible call to nlmsg_free() (i.e., no double-free).

Brian