3.16.47-rc1 review patch.  If anyone has any objections, please let me know.

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

From: "Michael J. Ruhl" <redacted>

commit 20c7840a77ddcb2ed2fbd66e8197db2868495751 upstream.

A list of MGID/MLID pairs is built when doing a multicast attach.  When
the multicast detach is called, the list is searched, and regardless of
the search outcome, the driver detach is called.

If an MGID/MLID pair is not on the list, driver detach should not be
called, and an error should be returned.  Calling the driver without
removing an MGID/MLID pair from the list can leave the core and driver
out of sync.

Fixes: f4e401562c11 ("IB/uverbs: track multicast group membership for userspace QPs")
Reviewed-by: Ira Weiny <redacted>
Reviewed-by: Leon Romanovsky <redacted>
Signed-off-by: Michael J. Ruhl <redacted>
Signed-off-by: Dennis Dalessandro <redacted>
Signed-off-by: Doug Ledford <redacted>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <redacted>
---
 drivers/infiniband/core/uverbs_cmd.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

--- a/drivers/infiniband/core/uverbs_cmd.c
+++ b/drivers/infiniband/core/uverbs_cmd.c

@@ -2577,6 +2577,7 @@ ssize_t ib_uverbs_detach_mcast(struct ib
 	struct ib_qp                 *qp;
 	struct ib_uverbs_mcast_entry *mcast;
 	int                           ret = -EINVAL;
+	bool                          found = false;
 
 	if (copy_from_user(&cmd, buf, sizeof cmd))
 		return -EFAULT;

@@ -2585,10 +2586,6 @@ ssize_t ib_uverbs_detach_mcast(struct ib
 	if (!qp)
 		return -EINVAL;
 
-	ret = ib_detach_mcast(qp, (union ib_gid *) cmd.gid, cmd.mlid);
-	if (ret)
-		goto out_put;
-
 	obj = container_of(qp->uobject, struct ib_uqp_object, uevent.uobject);
 
 	list_for_each_entry(mcast, &obj->mcast_list, list)

@@ -2596,9 +2593,17 @@ ssize_t ib_uverbs_detach_mcast(struct ib
 		    !memcmp(cmd.gid, mcast->gid.raw, sizeof mcast->gid.raw)) {
 			list_del(&mcast->list);
 			kfree(mcast);
+			found = true;
 			break;
 		}
 
+	if (!found) {
+		ret = -EINVAL;
+		goto out_put;
+	}
+
+	ret = ib_detach_mcast(qp, (union ib_gid *)cmd.gid, cmd.mlid);
+
 out_put:
 	put_qp_write(qp);