mm/vmalloc.c:__vmalloc_area_node(): avoid 32-bit overflow

mainline inclusion
from mainline-v5.11-rc1
commit 34fe6537
category: bugfix
bugzilla: NA
CVE: NA

-----------------------------------------------

With a machine with 3 TB (more than 2 TB memory).  If you use vmalloc to
allocate > 2 TB memory, the array_size below will be overflowed.

The array_size is an unsigned int and can only be used to allocate less
than 2 TB memory.  If you pass 2*1028*1028*1024*1024 = 2 * 2^40 in the
argument of vmalloc.  The array_size will become 2*2^31 = 2^32.  The 2^32
cannot be store with a 32 bit integer.

The fix is to change the type of array_size to unsigned long.

[akpm@linux-foundation.org: rework for current mainline]

Link: https://bugzilla.kernel.org/show_bug.cgi?id=210023
Reported-by: <hsinhuiwu@gmail.com>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

conflict:
	mm/vmalloc.c
Signed-off-by: NTong Tiangen <tongtiangen@huawei.com>
Reviewed-by: NChen Wandun <chenwandun@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

mm/vmalloc.c

@@ -2250,7 +2250,9 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
 				 pgprot_t prot, int node)
 {
 	struct page **pages;
-	unsigned int nr_pages, array_size, i;
+	unsigned int nr_pages;
+	unsigned long array_size;
+	unsigned int i;
 	const gfp_t nested_gfp = (gfp_mask & GFP_RECLAIM_MASK) | __GFP_ZERO;
 	const gfp_t alloc_mask = gfp_mask | __GFP_NOWARN;
 	const gfp_t highmem_mask = (gfp_mask & (GFP_DMA | GFP_DMA32)) ?
@@ -2258,7 +2260,7 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
 					__GFP_HIGHMEM;
 
 	nr_pages = get_vm_area_size(area) >> PAGE_SHIFT;
-	array_size = (nr_pages * sizeof(struct page *));
+	array_size = (unsigned long)nr_pages * sizeof(struct page *);
 
 	/* Please note that the recursion is strictly bounded. */
 	if (array_size > PAGE_SIZE) {