[patch 4/9] IB/uverbs: Fix checking of userspace object ownership

[Greg KH <gregkh@suse.de>]

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2.6.22-stable review patch.  If anyone has any objections, please let us
know.

------------------
From: Roland Dreier <rolandd@cisco.com>

Upstream as cbfb50e6e2e9c580848c0f51d37c24cdfb1cb704

Commit 9ead190b ("IB/uverbs: Don't serialize with ib_uverbs_idr_mutex")
rewrote how userspace objects are looked up in the uverbs module's
idrs, and introduced a severe bug in the process: there is no checking
that an operation is being performed by the right process any more.
Fix this by adding the missing check of uobj->context in __idr_get_uobj().

Apparently everyone is being very careful to only touch their own
objects, because this bug was introduced in June 2006 in 2.6.18, and
has gone undetected until now.

Signed-off-by: Roland Dreier <rolandd@cisco.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
 drivers/infiniband/core/uverbs_cmd.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

--- a/drivers/infiniband/core/uverbs_cmd.c
+++ b/drivers/infiniband/core/uverbs_cmd.c
@@ -147,8 +147,12 @@ static struct ib_uobject *__idr_get_uobj
 
 	spin_lock(&ib_uverbs_idr_lock);
 	uobj = idr_find(idr, id);
-	if (uobj)
-		kref_get(&uobj->ref);
+	if (uobj) {
+		if (uobj->context == context)
+			kref_get(&uobj->ref);
+		else
+			uobj = NULL;
+	}
 	spin_unlock(&ib_uverbs_idr_lock);
 
 	return uobj;

--