linux-kernel - [PATCH 4.18 107/150] llc: set SOCK_RCU_FREE in llc_sap_add

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Message-Id: <20181102182910.709949717@linuxfoundation.org>
Date:   Fri,  2 Nov 2018 19:34:29 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        syzbot+11e05f04c15e03be5254@...kaller.appspotmail.com,
        Cong Wang <xiyou.wangcong@...il.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 4.18 107/150] llc: set SOCK_RCU_FREE in llc_sap_add_socket()

4.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Cong Wang <xiyou.wangcong@...il.com>

[ Upstream commit 5a8e7aea953bdb6d4da13aff6f1e7f9c62023499 ]

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@...kaller.appspotmail.com
Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/llc/llc_conn.c |    1 +
 1 file changed, 1 insertion(+)

--- a/net/llc/llc_conn.c
+++ b/net/llc/llc_conn.c
@@ -734,6 +734,7 @@ void llc_sap_add_socket(struct llc_sap *
 	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);