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().
Signed-off-by: Julius Werner <jwer...@chromium.org>
---
drivers/usb/host/xhci-mem.c | 8 ++++++--
1 files changed, 6 insertions(+), 2 deletions(-)
diff --git a/drivers/usb/host/xhci-mem.c b/drivers/usb/host/xhci-mem.c
index 487bc08..420ba37 100644
--- a/drivers/usb/host/xhci-mem.c
+++ b/drivers/usb/host/xhci-mem.c
@@ -205,7 +205,11 @@ 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;
+ do {
+ next = prev->next;
+ xhci_segment_free(xhci, prev);
+ } while ((prev = next));
return -ENOMEM;
}
xhci_link_segments(xhci, prev, next, type);
@@ -258,7 +262,7 @@ static struct xhci_ring *xhci_ring_alloc(struct xhci_hcd
*xhci,
return ring;
fail:
- xhci_ring_free(xhci, ring);
+ kfree(ring);
return NULL;
}
--
1.7.8.6
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