netdev - [PATCH] llc: Fix race condition in llc_ui

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Message-Id: <1326981477-1698-1-git-send-email-riliescu@ixiacom.com>
Date:	Thu, 19 Jan 2012 15:57:57 +0200
From:	Radu Iliescu <radui@...csys.com>
To:	acme@...stprotocols.net, davem@...emloft.net
Cc:	netdev@...r.kernel.org, dbaluta@...acom.com,
	Radu Iliescu <riliescu@...acom.com>
Subject: [PATCH] llc: Fix race condition in llc_ui_recvmsg

There is a race on sk_receive_queue between llc_ui_recvmsg and
sock_queue_rcv_skb.

Our current solution is to protect skb_eat in llc_ui_recvmsg
with the queue spinlock.

Perhaps there is a better solution.
Maybe there is a lock missing in llc_sap_state_process or above.
I've tried to follow the locking in tcp on sk_receive_queue,
but is not clear how is done.

Please take a look and comment.

Signed-off-by: Radu Iliescu <riliescu@...acom.com>
---
 net/llc/af_llc.c |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/net/llc/af_llc.c b/net/llc/af_llc.c
index a18e6c3..46a60a4 100644
--- a/net/llc/af_llc.c
+++ b/net/llc/af_llc.c
@@ -719,6 +719,7 @@ static int llc_ui_recvmsg(struct kiocb *iocb, struct socket *sock,
 	unsigned long used;
 	int target;	/* Read at least this many bytes */
 	long timeo;
+	long cpu_flags;
 
 	lock_sock(sk);
 	copied = -ENOTCONN;
@@ -838,7 +839,9 @@ static int llc_ui_recvmsg(struct kiocb *iocb, struct socket *sock,
 			goto copy_uaddr;
 
 		if (!(flags & MSG_PEEK)) {
+			spin_lock_irqsave(&sk->sk_receive_queue.lock, cpu_flags);
 			sk_eat_skb(sk, skb, 0);
+			spin_unlock_irqrestore(&sk->sk_receive_queue.lock, cpu_flags);
 			*seq = 0;
 		}
 
@@ -859,7 +862,9 @@ copy_uaddr:
 		llc_cmsg_rcv(msg, skb);
 
 	if (!(flags & MSG_PEEK)) {
+			spin_lock_irqsave(&sk->sk_receive_queue.lock, cpu_flags);
 			sk_eat_skb(sk, skb, 0);
+			spin_unlock_irqrestore(&sk->sk_receive_queue.lock, cpu_flags);
 			*seq = 0;
 	}
 
-- 
1.7.0.4

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