msm: kgsl: Add missing checks for alloc size and sglen

In _kgsl_sharedmem_page_alloc():

- Make len of type size_t to be in line with size.
- Check for boundary limits of requested alloc size before honoring.
- Make sure sglen is greater than zero before marking it as end
of sg list.

Bug: 27475454
Change-Id: I5389bcef3478f2ccf2be5f719049867496235f28
Signed-off-by: Yuan Lin <yualin@google.com>

drivers/gpu/msm/kgsl_sharedmem.c

@@ -580,10 +580,15 @@ _kgsl_sharedmem_page_alloc(struct kgsl_memdesc *memdesc,
 			size_t size)
 {
 	int order, ret = 0;
-	int len, page_size, sglen_alloc, sglen = 0;
+	int page_size, sglen_alloc, sglen = 0;
 	void *ptr;
+	size_t len;
 	unsigned int align;
 
+	size = PAGE_ALIGN(size);
+	if (size == 0 || size > UINT_MAX)
+		return -EINVAL;
+
 	align = (memdesc->flags & KGSL_MEMALIGN_MASK) >> KGSL_MEMALIGN_SHIFT;
 
 	page_size = (align >= ilog2(SZ_64K) && size >= SZ_64K)