[PATCH 3.16 081/254] xhci: Don't add a virt_dev to the devs array before it's fully allocated

Ben Hutchings
2018-02-28T15:20:18Z

From: Mathias Nyman <mathias.nyman@linux.intel.com>

commit 5d9b70f7d52eb14bb37861c663bae44de9521c35 upstream.

Avoid null pointer dereference if some function is walking through the
devs array accessing members of a new virt_dev that is mid allocation.

Add the virt_dev to xhci->devs[i] _after_ the virt_device and all its
members are properly allocated.

issue found by KASAN: null-ptr-deref in xhci_find_slot_id_by_port

"Quick analysis suggests that xhci_alloc_virt_device() is not mutex
protected. If so, there is a time frame where xhci->devs[slot_id] is set
but not fully initialized. Specifically, xhci->devs[i]->udev can be NULL."

Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[bwh: Backported to 3.16: There is an extra failure path, so we may need to
free dev->eps[0].ring]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
--- a/drivers/usb/host/xhci-mem.c
+++ b/drivers/usb/host/xhci-mem.c
@@ -1018,10 +1018,9 @@ int xhci_alloc_virt_device(struct xhci_h
return 0;
}

- xhci->devs[slot_id] = kzalloc(sizeof(*xhci->devs[slot_id]), flags);
- if (!xhci->devs[slot_id])
+ dev = kzalloc(sizeof(*dev), flags);
+ if (!dev)
return 0;
- dev = xhci->devs[slot_id];

/* Allocate the (output) device context that will be used in the HC. */
dev->out_ctx = xhci_alloc_container_ctx(xhci, XHCI_CTX_TYPE_DEVICE, flags);
@@ -1069,9 +1068,19 @@ int xhci_alloc_virt_device(struct xhci_h
&xhci->dcbaa->dev_context_ptrs[slot_id],
le64_to_cpu(xhci->dcbaa->dev_context_ptrs[slot_id]));

+ xhci->devs[slot_id] = dev;
+
return 1;
fail:
- xhci_free_virt_device(xhci, slot_id);
+
+ if (dev->eps[0].ring)
+ xhci_ring_free(xhci, dev->eps[0].ring);
+ if (dev->in_ctx)
+ xhci_free_container_ctx(xhci, dev->in_ctx);
+ if (dev->out_ctx)
+ xhci_free_container_ctx(xhci, dev->out_ctx);
+ kfree(dev);
+
return 0;
}