linux-kernel - Re: [patch 1/1] Convert the semaphore to a mutex in net/tipc/socket.c

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Date:	Tue, 11 Dec 2007 16:44:45 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Kevin Winchester <kjwinchester@...il.com>
Cc:	mingo@...e.hu, per.liden@...csson.com, jon.maloy@...csson.com,
	allan.stephens@...driver.com,
	tipc-discussion@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org, kjwinchester@...il.com,
	netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>
Subject: Re: [patch 1/1] Convert the semaphore to a mutex in
 net/tipc/socket.c

On Sun, 09 Dec 2007 21:17:42 -0400
Kevin Winchester <kjwinchester@...il.com> wrote:

> Note also that in the release method, down_interruptible() was being called
> without checking the return value.  I converted it to mutex_lock_interruptible()
> and made the interrupted case return -ERESTARTSYS, as was done for all other
> calls to down_interruptible() in the file.

That's an outright bug.

static int release(struct socket *sock)
{
	struct tipc_sock *tsock = tipc_sk(sock->sk);
	struct sock *sk = sock->sk;
	int res = TIPC_OK;
	struct sk_buff *buf;

	dbg("sock_delete: %x\n",tsock);
	if (!tsock)
		return 0;
	down_interruptible(&tsock->sem);
	if (!sock->sk) {
		up(&tsock->sem);
		return 0;
	}

	...

	up(&tsock->sem);

	...	
}

So if the calling process has signal_pending(), down_interruptible() will
return without having downed the semaphore and then we merrily proceed to
do up() on it, so a subsequent down() won't actually take the lock and
things will deteriorate from there.

So I'd propose this:

--- a/net/tipc/socket.c~a
+++ a/net/tipc/socket.c
@@ -253,7 +253,7 @@ static int release(struct socket *sock)
 	dbg("sock_delete: %x\n",tsock);
 	if (!tsock)
 		return 0;
-	down_interruptible(&tsock->sem);
+	down(&tsock->sem);
 	if (!sock->sk) {
 		up(&tsock->sem);
 		return 0;
_

as a for-2.6.24 bugfix.  And for 2.6.23.  But someone who knows what
they're doing should take a look at this...

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