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+0bf2e01269f1274b4...@syzkaller.appspotmail.com
> Reported-by: syzbot+e3132895630f95730...@syzkaller.appspotmail.com
> Signed-off-by: Myungho Jung <mhju...@gmail.com>
> ---
> 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.
> + 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)
>
