linux-kernel - Re: slab corruption with current -git (was Re: [git pull] vfs pile 1 (splice))

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Message-ID: <CA+55aFzcweyWCqq-fRAnJkFB7neKwKsXH=TMcLtRQRs2Wn6XEQ@mail.gmail.com>
Date:   Mon, 10 Oct 2016 22:39:04 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Aaron Conole <aconole@...hat.com>
Cc:     Florian Westphal <fw@...len.de>, Al Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jens Axboe <axboe@...com>, "Ted Ts'o" <tytso@....edu>,
        Christoph Lameter <cl@...ux.com>,
        David Miller <davem@...emloft.net>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        NetFilter <netfilter-devel@...r.kernel.org>
Subject: Re: slab corruption with current -git (was Re: [git pull] vfs pile 1 (splice))

On Sun, Oct 9, 2016 at 8:41 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> This COMPLETELY UNTESTED patch tries to fix the nf_hook_entry code to do this.
>
> I repeat: it's ENTIRELY UNTESTED.

Gaah.

That patch was subtle garbage.

The "add to list" thing did this:

        rcu_assign_pointer(entry->next, p);
        rcu_assign_pointer(*pp, p);

which is not so subtly broken - that second assignment just assigns
"p" to "*pp", but that was what *pp already contained. Too much
cut-and-paste.

That also explains why I then get the NOT FOUND case, because the add
never actually worked.

It *should* be

        rcu_assign_pointer(entry->next, p);
        rcu_assign_pointer(*pp, entry);

and then the warnings about "not found" are gone.

Duh.

I guess I will have to double-check that the slub corruption is gone
still with that fixed.

Anyway, new version of the patch (just that one line changed) attached.

                Linus

View attachment "patch.diff" of type "text/plain" (5012 bytes)