[023/222] xhci: fix null-pointer dereference when destroying half-built segment rings

Message ID 1358351822-7675-24-git-send-email-herton.krzesinski@canonical.com
State New
Headers show

Commit Message

Herton Ronaldo Krzesinski Jan. 16, 2013, 3:53 p.m. -stable review patch.  If anyone has any objections, please let me know.


From: Julius Werner <jwerner@chromium.org>

commit 68e5254adb88bede68285f11fb442a4d34fb550c upstream.

xhci_alloc_segments_for_ring() builds a list of xhci_segments and links
the tail to head at the end (forming a ring). When it bails out for OOM
reasons half-way through, it tries to destroy its half-built list with
xhci_free_segments_for_ring(), even though it is not a ring yet. This
causes a null-pointer dereference upon hitting the last element.

Furthermore, one of its callers (xhci_ring_alloc()) mistakenly believes
the output parameters to be valid upon this kind of OOM failure, and
calls xhci_ring_free() on them. Since the (incomplete) list/ring should
already be destroyed in that case, this would lead to a use after free.

This patch fixes those issues by having xhci_alloc_segments_for_ring()
destroy its half-built, non-circular list manually and destroying the
invalid struct xhci_ring in xhci_ring_alloc() with a plain kfree().

This patch should be backported to kernels as old as 2.6.31, that
contains the commit 0ebbab37422315a5d0cb29792271085bafdf38c0 "USB: xhci:
Ring allocation and initialization."

A separate patch will need to be developed for kernels older than 3.4,
since the ring allocation code was refactored in that kernel.

Signed-off-by: Julius Werner <jwerner@chromium.org>
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski@canonical.com>
 drivers/usb/host/xhci-mem.c |    9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)


diff --git a/drivers/usb/host/xhci-mem.c b/drivers/usb/host/xhci-mem.c
index 487bc08..fb51c70 100644
--- a/drivers/usb/host/xhci-mem.c
+++ b/drivers/usb/host/xhci-mem.c
@@ -205,7 +205,12 @@  static int xhci_alloc_segments_for_ring(struct xhci_hcd *xhci,
 		next = xhci_segment_alloc(xhci, cycle_state, flags);
 		if (!next) {
-			xhci_free_segments_for_ring(xhci, *first);
+			prev = *first;
+			while (prev) {
+				next = prev->next;
+				xhci_segment_free(xhci, prev);
+				prev = next;
+			}
 			return -ENOMEM;
 		xhci_link_segments(xhci, prev, next, type);
@@ -258,7 +263,7 @@  static struct xhci_ring *xhci_ring_alloc(struct xhci_hcd *xhci,
 	return ring;
-	xhci_ring_free(xhci, ring);
+	kfree(ring);
 	return NULL;