| From 68e5254adb88bede68285f11fb442a4d34fb550c Mon Sep 17 00:00:00 2001 |
| From: Julius Werner <jwerner@chromium.org> |
| Date: Thu, 1 Nov 2012 12:47:59 -0700 |
| Subject: xhci: fix null-pointer dereference when destroying half-built segment rings |
| |
| 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: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| drivers/usb/host/xhci-mem.c | 9 +++++++-- |
| 1 file changed, 7 insertions(+), 2 deletions(-) |
| |
| --- 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( |
| |
| 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 |
| return ring; |
| |
| fail: |
| - xhci_ring_free(xhci, ring); |
| + kfree(ring); |
| return NULL; |
| } |
| |
