linux-kernel - Re: [PATCH] net: Fix suspicious RCU usage in bpf_sk_reuseport

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Date:   Tue, 16 Aug 2022 18:39:30 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Martin KaFai Lau <kafai@...com>
Cc:     David Howells <dhowells@...hat.com>,
        Hawkins Jiawei <yin31149@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        bpf@...r.kernel.org, Jakub Sitnicki <jakub@...udflare.com>
Subject: Re: [PATCH] net: Fix suspicious RCU usage in
 bpf_sk_reuseport_detach()

On Tue, 16 Aug 2022 17:43:19 -0700 Martin KaFai Lau wrote:
> > I like your version because it documents what the lock protecting this
> > field is.
> > 
> > In fact should we also add && sock_owned_by_user(). Martin, WDYT? Would
> > that work for reuseport? Jakub S is fixing l2tp to hold the socket lock
> > while setting this field, yet most places take the callback lock...  
>
> It needs to take a closer look at where the lock_sock() has already
> been acquired and also need to consider the lock ordering with reuseport_lock.
> It probably should work but may need a separate patch to discuss those
> considerations ?

Right, the users of the field with a bit allocated protect the writes
with the callback lock, so we can hard code the check against the
callback lock for now and revisit later if needed.