linux-kernel - [PATCH 3.16.y-ckt 044/126] tcp: md5: fix lockdep annotation

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Message-Id: <1452076655-12851-45-git-send-email-luis.henriques@canonical.com>
Date:	Wed,  6 Jan 2016 10:36:13 +0000
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Eric Dumazet <edumazet@...gle.com>,
	"David S. Miller" <davem@...emloft.net>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 044/126] tcp: md5: fix lockdep annotation

3.16.7-ckt22 -stable review patch.  If anyone has any objections, please let me know.

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

From: Eric Dumazet <edumazet@...gle.com>

commit 1b8e6a01e19f001e9f93b39c32387961c91ed3cc upstream.

When a passive TCP is created, we eventually call tcp_md5_do_add()
with sk pointing to the child. It is not owner by the user yet (we
will add this socket into listener accept queue a bit later anyway)

But we do own the spinlock, so amend the lockdep annotation to avoid
following splat :

[ 8451.090932] net/ipv4/tcp_ipv4.c:923 suspicious rcu_dereference_protected() usage!
[ 8451.090932]
[ 8451.090932] other info that might help us debug this:
[ 8451.090932]
[ 8451.090934]
[ 8451.090934] rcu_scheduler_active = 1, debug_locks = 1
[ 8451.090936] 3 locks held by socket_sockopt_/214795:
[ 8451.090936]  #0:  (rcu_read_lock){.+.+..}, at: [<ffffffff855c6ac1>] __netif_receive_skb_core+0x151/0xe90
[ 8451.090947]  #1:  (rcu_read_lock){.+.+..}, at: [<ffffffff85618143>] ip_local_deliver_finish+0x43/0x2b0
[ 8451.090952]  #2:  (slock-AF_INET){+.-...}, at: [<ffffffff855acda5>] sk_clone_lock+0x1c5/0x500
[ 8451.090958]
[ 8451.090958] stack backtrace:
[ 8451.090960] CPU: 7 PID: 214795 Comm: socket_sockopt_

[ 8451.091215] Call Trace:
[ 8451.091216]  <IRQ>  [<ffffffff856fb29c>] dump_stack+0x55/0x76
[ 8451.091229]  [<ffffffff85123b5b>] lockdep_rcu_suspicious+0xeb/0x110
[ 8451.091235]  [<ffffffff8564544f>] tcp_md5_do_add+0x1bf/0x1e0
[ 8451.091239]  [<ffffffff85645751>] tcp_v4_syn_recv_sock+0x1f1/0x4c0
[ 8451.091242]  [<ffffffff85642b27>] ? tcp_v4_md5_hash_skb+0x167/0x190
[ 8451.091246]  [<ffffffff85647c78>] tcp_check_req+0x3c8/0x500
[ 8451.091249]  [<ffffffff856451ae>] ? tcp_v4_inbound_md5_hash+0x11e/0x190
[ 8451.091253]  [<ffffffff85647170>] tcp_v4_rcv+0x3c0/0x9f0
[ 8451.091256]  [<ffffffff85618143>] ? ip_local_deliver_finish+0x43/0x2b0
[ 8451.091260]  [<ffffffff856181b6>] ip_local_deliver_finish+0xb6/0x2b0
[ 8451.091263]  [<ffffffff85618143>] ? ip_local_deliver_finish+0x43/0x2b0
[ 8451.091267]  [<ffffffff85618d38>] ip_local_deliver+0x48/0x80
[ 8451.091270]  [<ffffffff85618510>] ip_rcv_finish+0x160/0x700
[ 8451.091273]  [<ffffffff8561900e>] ip_rcv+0x29e/0x3d0
[ 8451.091277]  [<ffffffff855c74b7>] __netif_receive_skb_core+0xb47/0xe90

Fixes: a8afca0329988 ("tcp: md5: protects md5sig_info with RCU")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Reported-by: Willem de Bruijn <willemb@...gle.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 net/ipv4/tcp_ipv4.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index b68fd0d65411..0fd3c84ffaf8 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -992,7 +992,8 @@ int tcp_md5_do_add(struct sock *sk, const union tcp_md5_addr *addr,
 	}
 
 	md5sig = rcu_dereference_protected(tp->md5sig_info,
-					   sock_owned_by_user(sk));
+					   sock_owned_by_user(sk) ||
+					   lockdep_is_held(&sk->sk_lock.slock));
 	if (!md5sig) {
 		md5sig = kmalloc(sizeof(*md5sig), gfp);
 		if (!md5sig)
--
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