llc: set SOCK_RCU_FREE in llc_sap_add_socket()

WHen an llc sock is added into the sk_laddr_hash of an llc_sap,
it is not marked with SOCK_RCU_FREE.

This causes that the sock could be freed while it is still being
read by __llc_lookup_established() with RCU read lock. sock is
refcounted, but with RCU read lock, nothing prevents the readers
getting a zero refcnt.

Fix it by setting SOCK_RCU_FREE in llc_sap_add_socket().

Reported-by: syzbot+11e05f04c15e03be5254@syzkaller.appspotmail.com
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/llc/llc_conn.c b/net/llc/llc_conn.c
index c0ac522b48a1404c6b06c1ac1d85dae463316768..4ff89cb7c86f785a175b048c0c7c6a82c2f8fe8c 100644 (file)
--- a/net/llc/llc_conn.c
+++ b/net/llc/llc_conn.c
@@ -734,6 +734,7 @@ void llc_sap_add_socket(struct llc_sap *sap, struct sock *sk)
        llc_sk(sk)->sap = sap;
 
        spin_lock_bh(&sap->sk_lock);
+       sock_set_flag(sk, SOCK_RCU_FREE);
        sap->sk_count++;
        sk_nulls_add_node_rcu(sk, laddr_hb);
        hlist_add_head(&llc->dev_hash_node, dev_hb);