[PATCH AUTOSEL 5.4 117/187] net/smc: add fallback check to connect()

Sasha Levin
2019-12-27T17:43:28Z

From: Ursula Braun <ubraun@linux.ibm.com>

[ Upstream commit 86434744fedf0cfe07a9eee3f4632c0e25c1d136 ]

FASTOPEN setsockopt() or sendmsg() may switch the SMC socket to fallback
mode. Once fallback mode is active, the native TCP socket functions are
called. Nevertheless there is a small race window, when FASTOPEN
setsockopt/sendmsg runs in parallel to a connect(), and switch the
socket into fallback mode before connect() takes the sock lock.
Make sure the SMC-specific connect setup is omitted in this case.

This way a syzbot-reported refcount problem is fixed, triggered by
different threads running non-blocking connect() and FASTOPEN_KEY
setsockopt.

Reported-by: syzbot+96d3f9ff6a86d37e44c8@syzkaller.appspotmail.com
Fixes: 6d6dd528d5af ("net/smc: fix refcount non-blocking connect() -part 2")
Signed-off-by: Ursula Braun <ubraun@linux.ibm.com>
Signed-off-by: Karsten Graul <kgraul@linux.ibm.com>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/smc/af_smc.c | 14 ++++++++------
1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
index 737b49909a7a..6a6d3b2aa5a9 100644
--- a/net/smc/af_smc.c
+++ b/net/smc/af_smc.c
@@ -854,6 +854,8 @@ static int smc_connect(struct socket *sock, struct sockaddr *addr,
goto out;

sock_hold(&smc->sk); /* sock put in passive closing */
+ if (smc->use_fallback)
+ goto out;
if (flags & O_NONBLOCK) {
if (schedule_work(&smc->connect_work))
smc->connect_nonblock = 1;
@@ -1716,8 +1718,6 @@ static int smc_setsockopt(struct socket *sock, int level, int optname,
sk->sk_err = smc->clcsock->sk->sk_err;
sk->sk_error_report(sk);
}
- if (rc)
- return rc;

if (optlen < sizeof(int))
return -EINVAL;
@@ -1725,6 +1725,8 @@ static int smc_setsockopt(struct socket *sock, int level, int optname,
return -EFAULT;

lock_sock(sk);
+ if (rc || smc->use_fallback)
+ goto out;
switch (optname) {
case TCP_ULP:
case TCP_FASTOPEN:
@@ -1736,15 +1738,14 @@ static int smc_setsockopt(struct socket *sock, int level, int optname,
smc_switch_to_fallback(smc);
smc->fallback_rsn = SMC_CLC_DECL_OPTUNSUPP;
} else {
- if (!smc->use_fallback)
- rc = -EINVAL;
+ rc = -EINVAL;
}
break;
case TCP_NODELAY:
if (sk->sk_state != SMC_INIT &&
sk->sk_state != SMC_LISTEN &&
sk->sk_state != SMC_CLOSED) {
- if (val && !smc->use_fallback)
+ if (val)
mod_delayed_work(system_wq, &smc->conn.tx_work,
0);
}
@@ -1753,7 +1754,7 @@ static int smc_setsockopt(struct socket *sock, int level, int optname,
if (sk->sk_state != SMC_INIT &&
sk->sk_state != SMC_LISTEN &&
sk->sk_state != SMC_CLOSED) {
- if (!val && !smc->use_fallback)
+ if (!val)
mod_delayed_work(system_wq, &smc->conn.tx_work,
0);
}
@@ -1764,6 +1765,7 @@ static int smc_setsockopt(struct socket *sock, int level, int optname,
default:
break;
}
+out:
release_sock(sk);

return rc;
--
2.20.1