From 3b2167cc50f31531ee7cae375801489d1105d547 Mon Sep 17 00:00:00 2001 From: Julius Werner Date: Thu, 1 Nov 2012 12:47:59 -0700 Subject: xhci: fix null-pointer dereference when destroying half-built segment rings 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 Signed-off-by: Sarah Sharp Signed-off-by: Julius Werner Signed-off-by: Sarah Sharp [bwh: Backported to 3.2: - Adjust context - Since segment allocation is done directly in xhci_ring_alloc(), walk the list starting from ring->first_seg when freeing] Signed-off-by: Ben Hutchings Signed-off-by: CAI Qian Signed-off-by: Greg Kroah-Hartman --- drivers/usb/host/xhci-mem.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/drivers/usb/host/xhci-mem.c b/drivers/usb/host/xhci-mem.c index a2b20fe..af65322 100644 --- a/drivers/usb/host/xhci-mem.c +++ b/drivers/usb/host/xhci-mem.c @@ -180,8 +180,15 @@ static struct xhci_ring *xhci_ring_alloc(struct xhci_hcd *xhci, struct xhci_segment *next; next = xhci_segment_alloc(xhci, flags); - if (!next) + if (!next) { + prev = ring->first_seg; + while (prev) { + next = prev->next; + xhci_segment_free(xhci, prev); + prev = next; + } goto fail; + } xhci_link_segments(xhci, prev, next, link_trbs, isoc); prev = next; @@ -201,7 +208,7 @@ static struct xhci_ring *xhci_ring_alloc(struct xhci_hcd *xhci, return ring; fail: - xhci_ring_free(xhci, ring); + kfree(ring); return NULL; } -- cgit v1.1