Subject: Re: [PATCH net-next 1/5] net: add TIME_WAIT logic to sk_to_full_sk()

From: Martin KaFai Lau <[email-masked]>
Date: Fri, 4 Oct 2024 17:36:51 -0700

On 10/4/24 2:56 PM, Eric Dumazet wrote:
> On Fri, Oct 4, 2024 at 9:16 PM Eric Dumazet <[email-masked]> wrote:
>>
>> TCP will soon attach TIME_WAIT sockets to some ACK and RST.
>>
>> Make sure sk_to_full_sk() detects this and does not return
>> a non full socket.
>>
>> Signed-off-by: Eric Dumazet <[email-masked]>
>> ---
>>   include/net/inet_sock.h | 4 +++-
>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/include/net/inet_sock.h b/include/net/inet_sock.h
>> index 394c3b66065e20d34594d6e2a2010c55bb457810..cec093b78151b9a3b95ad4b3672a72b0aa9a8305 100644
>> --- a/include/net/inet_sock.h
>> +++ b/include/net/inet_sock.h
>> @@ -319,8 +319,10 @@ static inline unsigned long inet_cmsg_flags(const struct inet_sock *inet)
>>   static inline struct sock *sk_to_full_sk(struct sock *sk)
>>   {
>>   #ifdef CONFIG_INET
>> -       if (sk && sk->sk_state == TCP_NEW_SYN_RECV)
>> +       if (sk && READ_ONCE(sk->sk_state) == TCP_NEW_SYN_RECV)
>>                  sk = inet_reqsk(sk)->rsk_listener;
>> +       if (sk && READ_ONCE(sk->sk_state) == TCP_TIME_WAIT)
>> +               sk = NULL;
>>   #endif
>>          return sk;
>>   }
> 
> It appears some callers do not check if the return value could be NULL.
> I will have to add in v2 :
> 
> diff --git a/include/linux/bpf-cgroup.h b/include/linux/bpf-cgroup.h
> index ce91d9b2acb9f8991150ceead4475b130bead438..c3ffb45489a6924c1bc80355e862e243ec195b01
> 100644
> --- a/include/linux/bpf-cgroup.h
> +++ b/include/linux/bpf-cgroup.h
> @@ -209,7 +209,7 @@ static inline bool cgroup_bpf_sock_enabled(struct sock *sk,
>          int __ret = 0;                                                         \
>          if (cgroup_bpf_enabled(CGROUP_INET_EGRESS) && sk) {                    \

The above "&& sk" test can probably be removed after the "__sk &&" addition below.

>                  typeof(sk) __sk = sk_to_full_sk(sk);                           \
> -               if (sk_fullsock(__sk) && __sk == skb_to_full_sk(skb) &&        \
> +               if (__sk && sk_fullsock(__sk) && __sk == skb_to_full_sk(skb) &&        \

sk_to_full_sk() includes the TCP_TIME_WAIT check now. I wonder if testing __sk
for NULL is good enough and the sk_fullsock(__sk) check can be removed also.

Thanks for working on this series. It is useful for the bpf prog.

>                      cgroup_bpf_sock_enabled(__sk, CGROUP_INET_EGRESS))         \
>                          __ret = __cgroup_bpf_run_filter_skb(__sk, skb,         \
>                                                        CGROUP_INET_EGRESS); \
> diff --git a/net/core/filter.c b/net/core/filter.c
> index bd0d08bf76bb8de39ca2ca89cda99a97c9b0a034..533025618b2c06efa31548708f21d9e0ccbdc68d
> 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -6778,7 +6778,7 @@ __bpf_sk_lookup(struct sk_buff *skb, struct
> bpf_sock_tuple *tuple, u32 len,
>                  /* sk_to_full_sk() may return (sk)->rsk_listener, so
> make sure the original sk
>                   * sock refcnt is decremented to prevent a request_sock leak.
>                   */
> -               if (!sk_fullsock(sk2))
> +               if (sk2 && !sk_fullsock(sk2))
>                          sk2 = NULL;
>                  if (sk2 != sk) {
>                          sock_gen_put(sk);
> @@ -6826,7 +6826,7 @@ bpf_sk_lookup(struct sk_buff *skb, struct
> bpf_sock_tuple *tuple, u32 len,
>                  /* sk_to_full_sk() may return (sk)->rsk_listener, so
> make sure the original sk
>                   * sock refcnt is decremented to prevent a request_sock leak.
>                   */
> -               if (!sk_fullsock(sk2))
> +               if (sk2 && !sk_fullsock(sk2))
>                          sk2 = NULL;
>                  if (sk2 != sk) {
>                          sock_gen_put(sk);
> @@ -7276,7 +7276,7 @@ BPF_CALL_1(bpf_get_listener_sock, struct sock *, sk)
>   {
>          sk = sk_to_full_sk(sk);
> 
> -       if (sk->sk_state == TCP_LISTEN && sock_flag(sk, SOCK_RCU_FREE))
> +       if (sk && sk->sk_state == TCP_LISTEN && sock_flag(sk, SOCK_RCU_FREE))
>                  return (unsigned long)sk;
> 
>          return (unsigned long)NULL;