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?
>
> > + 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)
> >
>
