linux-kernel - [PATCH 4.19 091/125] usb: gadget: composite: Fix possible double free memory bug

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Date:   Mon, 11 Nov 2019 19:28:50 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Chandana Kishori Chiluveru <cchiluve@...eaurora.org>,
        Felipe Balbi <felipe.balbi@...ux.intel.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.19 091/125] usb: gadget: composite: Fix possible double free memory bug

From: Chandana Kishori Chiluveru <cchiluve@...eaurora.org>

[ Upstream commit 1c20c89b0421b52b2417bb0f62a611bc669eda1d ]

composite_dev_cleanup call from the failure of configfs_composite_bind
frees up the cdev->os_desc_req and cdev->req. If the previous calls of
bind and unbind is successful these will carry stale values.

Consider the below sequence of function calls:
configfs_composite_bind()
        composite_dev_prepare()
                - Allocate cdev->req, cdev->req->buf
        composite_os_desc_req_prepare()
                - Allocate cdev->os_desc_req, cdev->os_desc_req->buf
configfs_composite_unbind()
        composite_dev_cleanup()
                - free the cdev->os_desc_req->buf and cdev->req->buf
Next composition switch
configfs_composite_bind()
        - If it fails goto err_comp_cleanup will call the
	  composite_dev_cleanup() function
        composite_dev_cleanup()
	        - calls kfree up with the stale values of cdev->req->buf and
		  cdev->os_desc_req from the previous configfs_composite_bind
		  call. The free call on these stale values leads to double free.

Hence, Fix this issue by setting request and buffer pointer to NULL after
kfree.

Signed-off-by: Chandana Kishori Chiluveru <cchiluve@...eaurora.org>
Signed-off-by: Felipe Balbi <felipe.balbi@...ux.intel.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/usb/gadget/composite.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/usb/gadget/composite.c b/drivers/usb/gadget/composite.c
index dfcabadeed01b..33115e19756c6 100644
--- a/drivers/usb/gadget/composite.c
+++ b/drivers/usb/gadget/composite.c
@@ -2156,14 +2156,18 @@ void composite_dev_cleanup(struct usb_composite_dev *cdev)
 			usb_ep_dequeue(cdev->gadget->ep0, cdev->os_desc_req);
 
 		kfree(cdev->os_desc_req->buf);
+		cdev->os_desc_req->buf = NULL;
 		usb_ep_free_request(cdev->gadget->ep0, cdev->os_desc_req);
+		cdev->os_desc_req = NULL;
 	}
 	if (cdev->req) {
 		if (cdev->setup_pending)
 			usb_ep_dequeue(cdev->gadget->ep0, cdev->req);
 
 		kfree(cdev->req->buf);
+		cdev->req->buf = NULL;
 		usb_ep_free_request(cdev->gadget->ep0, cdev->req);
+		cdev->req = NULL;
 	}
 	cdev->next_string_id = 0;
 	device_remove_file(&cdev->gadget->dev, &dev_attr_suspended);
-- 
2.20.1