linux-kernel - Re: KASAN: invalid-free in p9stat

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Date:   Tue, 28 Aug 2018 00:40:37 +0200
From:   Dominique Martinet <asmadeus@...ewreck.org>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     syzbot <syzbot+d4252148d198410b864f@...kaller.appspotmail.com>,
        David Miller <davem@...emloft.net>,
        Eric Van Hensbergen <ericvh@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Latchesar Ionkov <lucho@...kov.net>,
        netdev <netdev@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        v9fs-developer@...ts.sourceforge.net
Subject: Re: KASAN: invalid-free in p9stat_free

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