linux-kernel - [PATCH 3.12 070/123] usb: xhci: Bugfix for NULL pointer deference in xhci_endpoint

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Message-Id: <d4ad72d1edd56c015dc1f6742c310768bf7dab00.1438699154.git.jslaby@suse.cz>
Date:	Tue,  4 Aug 2015 16:40:14 +0200
From:	Jiri Slaby <jslaby@...e.cz>
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, AMAN DEEP <aman.deep@...sung.com>,
	Mathias Nyman <mathias.nyman@...ux.intel.com>,
	Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 070/123] usb: xhci: Bugfix for NULL pointer deference in xhci_endpoint_init() function

From: AMAN DEEP <aman.deep@...sung.com>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

commit 3496810663922617d4b706ef2780c279252ddd6a upstream.

virt_dev->num_cached_rings counts on freed ring and is not updated
correctly. In xhci_free_or_cache_endpoint_ring() function, the free ring
is added into cache and then num_rings_cache is incremented as below:
		virt_dev->ring_cache[rings_cached] =
			virt_dev->eps[ep_index].ring;
		virt_dev->num_rings_cached++;
here, free ring pointer is added to a current index and then
index is incremented.
So current index always points to empty location in the ring cache.
For getting available free ring, current index should be decremented
first and then corresponding ring buffer value should be taken from ring
cache.

But In function xhci_endpoint_init(), the num_rings_cached index is
accessed before decrement.
		virt_dev->eps[ep_index].new_ring =
			virt_dev->ring_cache[virt_dev->num_rings_cached];
		virt_dev->ring_cache[virt_dev->num_rings_cached] = NULL;
		virt_dev->num_rings_cached--;
This is bug in manipulating the index of ring cache.
And it should be as below:
		virt_dev->num_rings_cached--;
		virt_dev->eps[ep_index].new_ring =
			virt_dev->ring_cache[virt_dev->num_rings_cached];
		virt_dev->ring_cache[virt_dev->num_rings_cached] = NULL;

Signed-off-by: Aman Deep <aman.deep@...sung.com>
Signed-off-by: Mathias Nyman <mathias.nyman@...ux.intel.com>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 drivers/usb/host/xhci-mem.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/usb/host/xhci-mem.c b/drivers/usb/host/xhci-mem.c
index 837c333c827f..9af524c1f48f 100644
--- a/drivers/usb/host/xhci-mem.c
+++ b/drivers/usb/host/xhci-mem.c
@@ -1331,10 +1331,10 @@ int xhci_endpoint_init(struct xhci_hcd *xhci,
 		/* Attempt to use the ring cache */
 		if (virt_dev->num_rings_cached == 0)
 			return -ENOMEM;
+		virt_dev->num_rings_cached--;
 		virt_dev->eps[ep_index].new_ring =
 			virt_dev->ring_cache[virt_dev->num_rings_cached];
 		virt_dev->ring_cache[virt_dev->num_rings_cached] = NULL;
-		virt_dev->num_rings_cached--;
 		xhci_reinit_cached_ring(xhci, virt_dev->eps[ep_index].new_ring,
 					1, type);
 	}
-- 
2.5.0

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