linux-kernel - qib_lookup_qpn() appears to leak pointer out of rcu_read

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Message-ID: <20140212003511.GA27242@linux.vnet.ibm.com>
Date:	Tue, 11 Feb 2014 16:35:11 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	roland@...nel.org, sean.hefty@...el.com, hal.rosenstock@...il.com
Cc:	linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: qib_lookup_qpn() appears to leak pointer out of rcu_read_unlock()

Hello!

The qib_lookup_qpn() function does RCU pointer traversals within RCU
read-side critical sections as required, but the qp pointer is returned
from this function after it does rcu_read_unlock().  One of the callers,
qib_rcv_hdrerr(), dereferences this pointer upon return.

This appears to me to be a bug.  From what I can see, the structure
pointed to by qp could be freed immediately after the rcu_read_unlock(),
which would result in a SEGV when qib_rcv_hdrerr() does its later
spin_lock(&qp->r_lock).

So what am I missing here?

							Thanx, Paul

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