Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Tue, 28 Aug 2018 00:40:37 +0200
From:   Dominique Martinet <asmadeus@codewreck.org>
To:     Dmitry Vyukov <dvyukov@google.com>
Cc:     syzbot <syzbot+d4252148d198410b864f@syzkaller.appspotmail.com>,
        David Miller <davem@davemloft.net>,
        Eric Van Hensbergen <ericvh@gmail.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Latchesar Ionkov <lucho@ionkov.net>,
        netdev <netdev@vger.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
        v9fs-developer@lists.sourceforge.net
Subject: Re: KASAN: invalid-free in p9stat_free
Message-ID: <20180827224037.GA18923@nautica>
References: <000000000000af648b057456e234@google.com>
 <20180827052412.GA26294@nautica>
 <CACT4Y+b1B5_Eg+j91GxaVbPk5sb8+SVOU_z5k9HYb4R716X9kQ@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <CACT4Y+b1B5_Eg+j91GxaVbPk5sb8+SVOU_z5k9HYb4R716X9kQ@mail.gmail.com>
User-Agent: Mutt/1.5.21 (2010-09-15)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Dmitry Vyukov wrote on Mon, Aug 27, 2018:
> kfree and then null pointer is pretty common, try to run:
> 
> find -name "*.c" -exec grep -A 1 "kfree(" {} \; | grep -B 1 " = NULL;"

Hmm, right, it looks like somewhere between 5 and 10% of the kfree()
calls are followed by NULL assignment, that's "common enough" - not
generalized but not rare either.

> Leaving dangling pointers behind is not the best idea.
> And from what I remember a bunch of similar double frees were fixed by
> nulling the pointer after the first kfree.

In this case it really is an error to call p9stat_free again, so let's
just do both.
Will send the patches shortly.


Thanks,
-- 
Dominique