Re: [PATCH] net: Fix suspicious RCU usage in bpf_sk_reuseport_detach()

From: Jakub Kicinski <kuba@kernel.org>
To: Martin KaFai Lau <kafai@fb.com>
Cc: David Howells <dhowells@redhat.com>,
	Hawkins Jiawei <yin31149@gmail.com>,
	"David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Paolo Abeni <pabeni@redhat.com>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andrii@kernel.org>,
	Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
	John Fastabend <john.fastabend@gmail.com>,
	KP Singh <kpsingh@kernel.org>,
	linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
	linux-kernel-mentees@lists.linuxfoundation.org,
	bpf@vger.kernel.org, Jakub Sitnicki <jakub@cloudflare.com>
Subject: Re: [PATCH] net: Fix suspicious RCU usage in bpf_sk_reuseport_detach()
Date: Tue, 16 Aug 2022 18:39:30 -0700	[thread overview]
Message-ID: <20220816183930.2328d46d@kernel.org> (raw)
In-Reply-To: <20220817004319.fd7dekpqeumbvmsh@kafai-mbp>

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.