[PATCH v3] IB/mlx4: Fix refcount leak in add_port() error path

[Guangshuo Li <lgs201920130244@gmail.com>]

After kobject_init_and_add(), the lifetime of the embedded struct
kobject is expected to be managed through the kobject core reference
counting.

In add_port(), if kobject_init_and_add() fails, the error path frees p
directly instead of releasing the kobject reference with kobject_put().
This may leave the reference count of the embedded struct kobject
unbalanced, resulting in a refcount leak and potentially leading to a
use-after-free.

The issue was identified by a static analysis tool I developed and
confirmed by manual review.

Fix this by using kobject_put(&p->kobj) in the kobject_init_and_add()
failure path.

Fixes: c1e7e466120b ("IB/mlx4: Add iov directory in sysfs under the ib device")
Cc: stable@vger.kernel.org
Signed-off-by: Guangshuo Li <lgs201920130244@gmail.com>
---
v3:
  - make mlx4_port_release() tolerate NULL attribute arrays
  - drop the parent kobject reference on the kobject_init_and_add()
    failure path before putting the embedded kobject

v2:
  - note that the issue was identified by my static analysis tool
  - and confirmed by manual review

 drivers/infiniband/hw/mlx4/sysfs.c | 25 ++++++++++++++++++-------
 1 file changed, 18 insertions(+), 7 deletions(-)

diff --git a/drivers/infiniband/hw/mlx4/sysfs.c b/drivers/infiniband/hw/mlx4/sysfs.c
index b8fa4ecfc961..38c64b5fb23a 100644
--- a/drivers/infiniband/hw/mlx4/sysfs.c
+++ b/drivers/infiniband/hw/mlx4/sysfs.c
@@ -380,12 +380,17 @@ static void mlx4_port_release(struct kobject *kobj)
 	struct attribute *a;
 	int i;
 
-	for (i = 0; (a = p->pkey_group.attrs[i]); ++i)
-		kfree(a);
-	kfree(p->pkey_group.attrs);
-	for (i = 0; (a = p->gid_group.attrs[i]); ++i)
-		kfree(a);
-	kfree(p->gid_group.attrs);
+	if (p->pkey_group.attrs) {
+		for (i = 0; (a = p->pkey_group.attrs[i]); ++i)
+			kfree(a);
+		kfree(p->pkey_group.attrs);
+	}
+
+	if (p->gid_group.attrs) {
+		for (i = 0; (a = p->gid_group.attrs[i]); ++i)
+			kfree(a);
+		kfree(p->gid_group.attrs);
+	}
 	kfree(p);
 }
 
@@ -640,7 +645,7 @@ static int add_port(struct mlx4_ib_dev *dev, int port_num, int slave)
 				   kobject_get(dev->dev_ports_parent[slave]),
 				   "%d", port_num);
 	if (ret)
-		goto err_alloc;
+		goto err_kobj;
 
 	p->pkey_group.name  = "pkey_idx";
 	p->pkey_group.attrs =
@@ -687,6 +692,12 @@ static int add_port(struct mlx4_ib_dev *dev, int port_num, int slave)
 	kobject_put(dev->dev_ports_parent[slave]);
 	kfree(p);
 	return ret;
+
+err_kobj:
+	kobject_put(dev->dev_ports_parent[slave]);
+	kobject_put(&p->kobj);
+	return ret;
+
 }
 
 static int register_one_pkey_tree(struct mlx4_ib_dev *dev, int slave)
-- 
2.43.0