[PATCH] mm/vmalloc: reject overflowing vm_map_ram page counts

["Shubhang Kaushik (Ampere)" <sh@gentwo.org>]

vm_map_ram() converts its unsigned int page count to an unsigned long
byte size without checking for overflow.

On 32-bit kernels, a count greater than ULONG_MAX >> PAGE_SHIFT wraps
the byte size.  vm_map_ram() passes that size to both alloc_vmap_area()
and vmap_pages_range(), so it can allocate and map only the wrapped
number of pages while returning success for the original larger request.

For example, with 4 KiB pages, a count of 1048577 produces a
PAGE_SIZE byte size after wrapping, allowing a one-page mapping.

Reject page counts whose byte size cannot be represented.

Fixes: db64fe02258f ("mm: rewrite vmap layer")
Signed-off-by: Shubhang Kaushik (Ampere) <sh@gentwo.org>
---
 mm/vmalloc.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index bea9f76ed7e74247d4ce919250c2f02dd5c36483..e98d3aa551fe205ebd9826daad9ad6bd578b91ea 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -3083,10 +3083,15 @@ EXPORT_SYMBOL(vm_unmap_ram);
  */
 void *vm_map_ram(struct page **pages, unsigned int count, int node)
 {
-	unsigned long size = (unsigned long)count << PAGE_SHIFT;
+	unsigned long size;
 	unsigned long addr;
 	void *mem;
 
+	if (count > ULONG_MAX >> PAGE_SHIFT)
+		return NULL;
+
+	size = (unsigned long)count << PAGE_SHIFT;
+
 	if (likely(count <= VMAP_MAX_ALLOC)) {
 		mem = vb_alloc(size, GFP_KERNEL);
 		if (IS_ERR(mem))

---
base-commit: 7be4bc52fd9e0e55dc9a2e0232b89427d2c4b614
change-id: 20261022-vmalloc-reject-overflow-e532c556f3fa

Best regards,
-- 
Shubhang Kaushik (Ampere) <sh@gentwo.org>