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

[Michal Luczaj <mhal@rbox.co>]

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@rbox.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.