linux-kernel - Re: [PATCH net 2/4] vsock/bpf: Warn on socket without transport

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Message-ID: <ff1d32c8-e01e-45e3-8811-eb19a5cb6960@rbox.co>
Date: Mon, 17 Feb 2025 20:45:06 +0100
From: Michal Luczaj <mhal@...x.co>
To: Stefano Garzarella <sgarzare@...hat.com>
Cc: John Fastabend <john.fastabend@...il.com>,
 Jakub Sitnicki <jakub@...udflare.com>, Eric Dumazet <edumazet@...gle.com>,
 Kuniyuki Iwashima <kuniyu@...zon.com>, Paolo Abeni <pabeni@...hat.com>,
 Willem de Bruijn <willemb@...gle.com>, "David S. Miller"
 <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>,
 Simon Horman <horms@...nel.org>, "Michael S. Tsirkin" <mst@...hat.com>,
 Bobby Eshleman <bobby.eshleman@...edance.com>,
 Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>,
 Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau
 <martin.lau@...ux.dev>, Eduard Zingerman <eddyz87@...il.com>,
 Song Liu <song@...nel.org>, Yonghong Song <yonghong.song@...ux.dev>,
 KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>,
 Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
 Mykola Lysenko <mykolal@...com>, Shuah Khan <shuah@...nel.org>,
 netdev@...r.kernel.org, bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-kselftest@...r.kernel.org
Subject: Re: [PATCH net 2/4] vsock/bpf: Warn on socket without transport

On 2/17/25 11:59, Stefano Garzarella wrote:
> On Thu, Feb 13, 2025 at 12:58:50PM +0100, Michal Luczaj wrote:
>> In the spirit of commit 91751e248256 ("vsock: prevent null-ptr-deref in
>> vsock_*[has_data|has_space]"), armorize the "impossible" cases with a
>> warning.
>>
>> Fixes: 634f1a7110b4 ("vsock: support sockmap")
>> Signed-off-by: Michal Luczaj <mhal@...x.co>
>> ---
>> net/vmw_vsock/af_vsock.c  | 3 +++
>> net/vmw_vsock/vsock_bpf.c | 2 +-
>> 2 files changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
>> index 53a081d49d28ac1c04e7f8057c8a55e7b73cc131..7e3db87ae4333cf63327ec105ca99253569bb9fe 100644
>> --- a/net/vmw_vsock/af_vsock.c
>> +++ b/net/vmw_vsock/af_vsock.c
>> @@ -1189,6 +1189,9 @@ static int vsock_read_skb(struct sock *sk, skb_read_actor_t read_actor)
>> {
>> 	struct vsock_sock *vsk = vsock_sk(sk);
>>
>> +	if (WARN_ON_ONCE(!vsk->transport))
>> +		return -ENODEV;
>> +
>> 	return vsk->transport->read_skb(vsk, read_actor);
>> }
>>
>> diff --git a/net/vmw_vsock/vsock_bpf.c b/net/vmw_vsock/vsock_bpf.c
>> index f201d9eca1df2f8143638cf7a4d08671e8368c11..07b96d56f3a577af71021b1b8132743554996c4f 100644
>> --- a/net/vmw_vsock/vsock_bpf.c
>> +++ b/net/vmw_vsock/vsock_bpf.c
>> @@ -87,7 +87,7 @@ static int vsock_bpf_recvmsg(struct sock *sk, struct msghdr *msg,
>> 	lock_sock(sk);
>> 	vsk = vsock_sk(sk);
>>
>> -	if (!vsk->transport) {
>> +	if (WARN_ON_ONCE(!vsk->transport)) {
>> 		copied = -ENODEV;
>> 		goto out;
>> 	}
> 
> I'm not a sockmap expert, so I don't understand why here print an
> error.
> 
> Since there was already a check, I expected it to be a case that can 
> happen, but instead calling `rcvmsg()` on a socket not yet connected is 
> impossible?

That's right, calling vsock_bpf_recvmsg() on a not-yet-connected
connectible socket is impossible since PATCH 1/4 of this series.

That is because to reach vsock_bpf_recvmsg(), you must have sock's proto
replaced in vsock_bpf_update_proto(). For that you need to run
sock_map_init_proto(), which you can't because the patched
sock_map_sk_state_allowed() will stop you.