[PATCH] mm/vmalloc: Sanitize __get_vm_area() arguments

[Peter Zijlstra <peterz@infradead.org>]

__get_vm_area() is an exported symbol, make sure the callers stay in
the expected memory range. When calling this function with memory
ranges outside of the VMALLOC range *bad* things can happen.

(I noticed this when I managed to corrupt the kernel text by accident)

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 mm/vmalloc.c |    7 +++++++
 1 file changed, 7 insertions(+)

--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2130,6 +2130,13 @@ static struct vm_struct *__get_vm_area_n
 struct vm_struct *__get_vm_area(unsigned long size, unsigned long flags,
 				unsigned long start, unsigned long end)
 {
+	/*
+	 * Ensure callers stay in the vmalloc range.
+	 */
+	if (WARN_ON(start < VMALLOC_START || start > VMALLOC_END ||
+		    end < VMALLOC_START || end > VMALLOC_END))
+		return NULL;
+
 	return __get_vm_area_node(size, 1, flags, start, end, NUMA_NO_NODE,
 				  GFP_KERNEL, __builtin_return_address(0));
 }