From 68e5254adb88bede68285f11fb442a4d34fb550c Mon Sep 17 00:00:00 2001 From: Julius Werner Date: Thu, 1 Nov 2012 12:47:59 -0700 Subject: [PATCH] xhci: fix null-pointer dereference when destroying half-built segment rings 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 Signed-off-by: Sarah Sharp Cc: stable@vger.kernel.org --- 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 487bc083dead..fb51c7085ad0 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; fail: - xhci_ring_free(xhci, ring); + kfree(ring); return NULL; } -- 2.20.1