tipc: fix race between poll() and setsockopt()

Letting tipc_poll() dereference a socket's pointer to struct tipc_group
entails a race risk, as the group item may be deleted in a concurrent
tipc_sk_join() or tipc_sk_leave() thread.

We now move the 'open' flag in struct tipc_group to struct tipc_sock,
and let the former retain only a pointer to the moved field. This will
eliminate the race risk.

Reported-by: syzbot+799dafde0286795858ac@syzkaller.appspotmail.com
Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 3 insertions, 4 deletions

diff --git a/net/tipc/socket.c b/net/tipc/socket.c
index d799e50ff722..473a096b6fba 100644
--- a/net/tipc/socket.c
+++ b/net/tipc/socket.c
@@ -116,6 +116,7 @@ struct tipc_sock {
         struct tipc_mc_method mc_method;
         struct rcu_head rcu;
         struct tipc_group *group;
+        bool group_is_open;
 };
 
 static int tipc_sk_backlog_rcv(struct sock *sk, struct sk_buff *skb);
@@ -715,7 +716,6 @@ static unsigned int tipc_poll(struct file *file, struct socket *sock,
 {
         struct sock *sk = sock->sk;
         struct tipc_sock *tsk = tipc_sk(sk);
-        struct tipc_group *grp;
         u32 revents = 0;
 
         sock_poll_wait(file, sk_sleep(sk), wait);
@@ -736,8 +736,7 @@ static unsigned int tipc_poll(struct file *file, struct socket *sock,
                         revents |= POLLIN | POLLRDNORM;
                 break;
         case TIPC_OPEN:
-                grp = tsk->group;
-                if ((!grp || tipc_group_is_open(grp)) && !tsk->cong_link_cnt)
+                if (tsk->group_is_open && !tsk->cong_link_cnt)
                         revents |= POLLOUT;
                 if (!tipc_sk_type_connectionless(sk))
                         break;
@@ -2758,7 +2757,7 @@ static int tipc_sk_join(struct tipc_sock *tsk, struct tipc_group_req *mreq)
                 return -EINVAL;
         if (grp)
                 return -EACCES;
-        grp = tipc_group_create(net, tsk->portid, mreq);
+        grp = tipc_group_create(net, tsk->portid, mreq, &tsk->group_is_open);
         if (!grp)
                 return -ENOMEM;
         tsk->group = grp;