[PATCH v2 1/6] dt-overlay: Fix NULL pointer dereference

[Michal Orzel <michal.orzel@xxxxxxx>]

Attempt to attach an overlay (xl dt-overlay attach) to a domain without
first adding this overlay to Xen (xl dt-overlay add) results in an
overlay track entry being NULL in handle_attach_overlay_nodes(). This
leads to NULL pointer dereference and the following data abort crash:

(XEN) Cannot find any matching tracker with input dtbo. Operation is supported 
only for prior added dtbo.
(XEN) Data Abort Trap. Syndrome=0x5
(XEN) Walking Hypervisor VA 0x40 on CPU0 via TTBR 0x0000000046948000
(XEN) 0TH[0x000] = 0x46940f7f
(XEN) 1ST[0x000] = 0x0
(XEN) CPU0: Unexpected Trap: Data Abort
(XEN) ----[ Xen-4.20-unstable  arm64  debug=y  Not tainted ]----
...
(XEN) Xen call trace:
(XEN)    [<00000a0000208b30>] dt_overlay_domctl+0x304/0x370 (PC)
(XEN)    [<00000a0000208b30>] dt_overlay_domctl+0x304/0x370 (LR)
(XEN)    [<00000a0000274b7c>] arch_do_domctl+0x48/0x328

Fixes: 4c733873b5c2 ("xen/arm: Add XEN_DOMCTL_dt_overlay and device attachment 
to domains")
Signed-off-by: Michal Orzel <michal.orzel@xxxxxxx>
Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
---
Changes in v2:
 - Add Rb
---
 xen/common/dt-overlay.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/xen/common/dt-overlay.c b/xen/common/dt-overlay.c
index d53b4706cd2f..8606b14d1e8e 100644
--- a/xen/common/dt-overlay.c
+++ b/xen/common/dt-overlay.c
@@ -908,8 +908,11 @@ static long handle_attach_overlay_nodes(struct domain *d,
  out:
     spin_unlock(&overlay_lock);
 
-    rangeset_destroy(entry->irq_ranges);
-    rangeset_destroy(entry->iomem_ranges);
+    if ( entry )
+    {
+        rangeset_destroy(entry->irq_ranges);
+        rangeset_destroy(entry->iomem_ranges);
+    }
 
     return rc;
 }
-- 
2.25.1