On 12/18/2018 08:03 AM, Myungho Jung wrote:
> On Mon, Dec 17, 2018 at 03:58:58PM +0100, Ursula Braun wrote:
>>
>
> Hi Ursula,
>
> Thank you for your suggestion. I have a question on your comment.
>
>>
>> On 12/17/2018 06:21 AM, Myungho Jung wrote:
>>> clcsock can be released while kernel_accept() references it in TCP
>>> listen worker. Also, clcsock needs to wake up before released if TCP
>>> fallback is used and the clcsock is blocked by accept. Add a lock to
>>> safely release clcsock and call kernel_sock_shutdown() to wake up
>>> clcsock from accept in smc_release().
>>
>> Thanks for your effort to solve this problem. I have some minor
>> improvement proposals:
>>
>>>
>>> Reported-by: syzbot+0bf2e01269f1274b4b03@xxxxxxxxxxxxxxxxxxxxxxxxx
>>> Reported-by: syzbot+e3132895630f957306bc@xxxxxxxxxxxxxxxxxxxxxxxxx
>>> Signed-off-by: Myungho Jung <mhjungk@xxxxxxxxx>
>>> ---
>>> net/smc/af_smc.c | 14 ++++++++++++--
>>> net/smc/smc.h | 2 ++
>>> 2 files changed, 14 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
>>> index 5fbaf1901571..5d06fb1bbccf 100644
>>> --- a/net/smc/af_smc.c
>>> +++ b/net/smc/af_smc.c
>>> @@ -147,8 +147,14 @@ static int smc_release(struct socket *sock)
>>> sk->sk_shutdown |= SHUTDOWN_MASK;
>>> }
>>> if (smc->clcsock) {
>>> + if (smc->use_fallback && sk->sk_state == SMC_LISTEN) {
>>> + /* wake up clcsock accept */
>>> + rc = kernel_sock_shutdown(smc->clcsock, SHUT_RDWR);
>>> + }
>>
>> This part is not needed, since an SMC socket in state SMC_LISTEN is never
>> a use_fallback socket.
>
> In smc_sendmsg(), set use_fallback to true if SMC socket is SMC_INIT
> state and the message has MSG_FASTOPEN flag. After this, smc_listen()
> would trigger smc_tcp_listen_work(). Is this not an expected scenario?
> Then, what is the reason for not skipping smc_sendmsg() in SMC_INIT
> state?
>
You are right, I have not had the FASTOPEN case in mind, sorry. If we want
to allow fallback in case of FASTOPEN, we need the kernel_sock_shutdown() here
for proper cleanup. Nice!
>>
>>> + mutex_lock(&smc->clcsock_release_lock);
>>> sock_release(smc->clcsock);
>>> smc->clcsock = NULL;
>>> + mutex_unlock(&smc->clcsock_release_lock);
>>> }
>>> if (smc->use_fallback) {
>>> if (sk->sk_state != SMC_LISTEN && sk->sk_state != SMC_INIT)
>>> @@ -205,6 +211,7 @@ static struct sock *smc_sock_alloc(struct net *net, struct socket *sock,
>>> spin_lock_init(&smc->conn.send_lock);
>>> sk->sk_prot->hash(sk);
>>> sk_refcnt_debug_inc(sk);
>>> + mutex_init(&smc->clcsock_release_lock);
>>>
>>> return sk;
>>> }
>>> @@ -821,7 +828,7 @@ static int smc_clcsock_accept(struct smc_sock *lsmc, struct smc_sock **new_smc)
>>> struct socket *new_clcsock = NULL;
>>> struct sock *lsk = &lsmc->sk;
>>> struct sock *new_sk;
>>> - int rc;
>>> + int rc = 0;
>>
>> Without clcsock the good path should not be executed. Thus I suggest
>> to initialize with something negative like -EINVAL.
>>
>>>
>>> release_sock(lsk);
>>> new_sk = smc_sock_alloc(sock_net(lsk), NULL, lsk->sk_protocol);
>>> @@ -834,7 +841,10 @@ static int smc_clcsock_accept(struct smc_sock *lsmc, struct smc_sock **new_smc)
>>> }
>>> *new_smc = smc_sk(new_sk);
>>>
>>> - rc = kernel_accept(lsmc->clcsock, &new_clcsock, 0);
>>> + mutex_lock(&lsmc->clcsock_release_lock);
>>> + if (lsmc->clcsock)
>>> + rc = kernel_accept(lsmc->clcsock, &new_clcsock, 0);
>>> + mutex_unlock(&lsmc->clcsock_release_lock);
>>> lock_sock(lsk);
>>> if (rc < 0)
>>> lsk->sk_err = -rc;
>>> diff --git a/net/smc/smc.h b/net/smc/smc.h
>>> index 08786ace6010..9a2795cf5d30 100644
>>> --- a/net/smc/smc.h
>>> +++ b/net/smc/smc.h
>>> @@ -219,6 +219,8 @@ struct smc_sock { /* smc sock container */
>>> * started, waiting for unsent
>>> * data to be sent
>>> */
>>> + struct mutex clcsock_release_lock;
>>> + /* protects clcsock */
>>
>> I suggest to be more precise: "protects clcsock of a listen socket"
>>
>>> };
>>>
>>> static inline struct smc_sock *smc_sk(const struct sock *sk)
>>>
>>
>
