[PATCH 5.10.y] xen/gntdev: Fix gntdev_dmabuf ref leak in dmabuf_exp_wait_released()

[Sasha Levin <sashal@kernel.org>]

From: Wentao Liang <vulab@iscas.ac.cn>

[ Upstream commit 6f165abe2b40ede71c98956cd74cd17c18505e75 ]

dmabuf_exp_wait_released() takes a reference on the exported
gntdev_dmabuf with dmabuf_exp_wait_obj_get_dmabuf() and passes it to
dmabuf_exp_wait_obj_new(), which drops that reference after adding the
wait object to the wait list.  When the wait object allocation fails,
dmabuf_exp_wait_obj_new() returns ERR_PTR(-ENOMEM) early and the
reference is never dropped, leaking a reference to the exported
gntdev_dmabuf.

Drop the reference on the allocation failure path so the reference is
consumed whether the wait object is created or not.

Fixes: 932d6562179e ("xen/gntdev: Add initial support for dma-buf UAPI")
Cc: stable@vger.kernel.org
Signed-off-by: Wentao Liang <vulab@iscas.ac.cn>
Reviewed-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Message-ID: <20260916170956.2086505-1-vulab@iscas.ac.cn>
[ sashal: adjusted allocation context for kzalloc(sizeof(*obj), GFP_KERNEL) instead of kzalloc_obj(*obj) ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/xen/gntdev-dmabuf.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/xen/gntdev-dmabuf.c b/drivers/xen/gntdev-dmabuf.c
index 398ea69c176c1..8ed7aba6a6734 100644
--- a/drivers/xen/gntdev-dmabuf.c
+++ b/drivers/xen/gntdev-dmabuf.c
@@ -102,8 +102,10 @@ dmabuf_exp_wait_obj_new(struct gntdev_dmabuf_priv *priv,
 	struct gntdev_dmabuf_wait_obj *obj;
 
 	obj = kzalloc(sizeof(*obj), GFP_KERNEL);
-	if (!obj)
+	if (!obj) {
+		kref_put(&gntdev_dmabuf->u.exp.refcount, dmabuf_exp_release);
 		return ERR_PTR(-ENOMEM);
+	}
 
 	init_completion(&obj->completion);
 	obj->gntdev_dmabuf = gntdev_dmabuf;
-- 
2.53.0