mm/vmalloc: use physical page count for vrealloc() grow-in-place check

Update the grow-in-place check in vrealloc() to compare the requested size
against the actual physical page count (vm->nr_pages) rather than the
virtual area size (alloced_size, derived from get_vm_area_size()).

Currently both values are equivalent, but the upcoming vrealloc() shrink
functionality will free pages without reducing the virtual reservation
size.  After such a shrink, the old alloced_size-based comparison would
incorrectly allow a grow-in-place operation to succeed and attempt to
access freed pages.  Switch to vm->nr_pages now so the check remains
correct once shrink support is added.

Link: https://lore.kernel.org/[email protected]
Signed-off-by: Shivam Kalra <[email protected]>
Reviewed-by: Uladzislau Rezki (Sony) <[email protected]>
Cc: Alice Ryhl <[email protected]>
Cc: Danilo Krummrich <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

mm/vmalloc.c

@@ -4343,6 +4343,12 @@ void *vrealloc_node_align_noprof(const void *p, size_t size, unsigned long align
 		if (unlikely(flags & __GFP_THISNODE) && nid != NUMA_NO_NODE &&
 			     nid != page_to_nid(vmalloc_to_page(p)))
 			goto need_realloc;
+	} else {
+		/*
+		 * If p is NULL, vrealloc behaves exactly like vmalloc.
+		 * Skip the shrink and in-place grow paths.
+		 */
+		goto need_realloc;
 	}
 
 	/*
@@ -4361,7 +4367,7 @@ void *vrealloc_node_align_noprof(const void *p, size_t size, unsigned long align
 	/*
 	 * We already have the bytes available in the allocation; use them.
 	 */
-	if (size <= alloced_size) {
+	if (size <= vm->nr_pages << PAGE_SHIFT) {
 		/*
 		 * No need to zero memory here, as unused memory will have
 		 * already been zeroed at initial allocation time or during