netdev - Re: [PATCH net v3] net: fix pos incrementment in ipv6_route_seq

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Message-ID: <20201015102358.0cdef2ca@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Thu, 15 Oct 2020 10:23:58 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Yonghong Song <yhs@...com>
Cc:     <bpf@...r.kernel.org>, <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>, <kernel-team@...com>,
        Andrii Nakryiko <andriin@...com>,
        Vasily Averin <vvs@...tuozzo.com>
Subject: Re: [PATCH net v3] net: fix pos incrementment in
 ipv6_route_seq_next

On Wed, 14 Oct 2020 07:46:12 -0700 Yonghong Song wrote:
> Commit 4fc427e05158 ("ipv6_route_seq_next should increase position index")
> tried to fix the issue where seq_file pos is not increased
> if a NULL element is returned with seq_ops->next(). See bug
>   https://bugzilla.kernel.org/show_bug.cgi?id=206283
> The commit effectively does:
>   - increase pos for all seq_ops->start()
>   - increase pos for all seq_ops->next()
> 
> For ipv6_route, increasing pos for all seq_ops->next() is correct.
> But increasing pos for seq_ops->start() is not correct
> since pos is used to determine how many items to skip during
> seq_ops->start():
>   iter->skip = *pos;
> seq_ops->start() just fetches the *current* pos item.
> The item can be skipped only after seq_ops->show() which essentially
> is the beginning of seq_ops->next().

Applied, queued for stable, thanks!