overflow.h: Add allocation size calculation helpers

In preparation for replacing unchecked overflows for memory allocations,
this creates helpers for the 3 most common calculations:

array_size(a, b): 2-dimensional array
array3_size(a, b, c): 3-dimensional array
struct_size(ptr, member, n): struct followed by n-many trailing members

Each of these return SIZE_MAX on overflow instead of wrapping around.

(Additionally renames a variable named "array_size" to avoid future
collision.)

Co-developed-by: Matthew Wilcox <mawilcox@microsoft.com>
Signed-off-by: Kees Cook <keescook@chromium.org>

1 files changed, 5 insertions, 5 deletions

diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 0589a4da12bb..caa51dd351b6 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -548,14 +548,14 @@ static int adjoin(struct dm_table *table, struct dm_target *ti)
  * On the other hand, dm-switch needs to process bulk data using messages and
  * excessive use of GFP_NOIO could cause trouble.
  */
-static char **realloc_argv(unsigned *array_size, char **old_argv)
+static char **realloc_argv(unsigned *size, char **old_argv)
 {
 	char **argv;
 	unsigned new_size;
 	gfp_t gfp;
 
-	if (*array_size) {
-		new_size = *array_size * 2;
+	if (*size) {
+		new_size = *size * 2;
 		gfp = GFP_KERNEL;
 	} else {
 		new_size = 8;
@@ -563,8 +563,8 @@ static char **realloc_argv(unsigned *array_size, char **old_argv)
 	}
 	argv = kmalloc(new_size * sizeof(*argv), gfp);
 	if (argv) {
-		memcpy(argv, old_argv, *array_size * sizeof(*argv));
-		*array_size = new_size;
+		memcpy(argv, old_argv, *size * sizeof(*argv));
+		*size = new_size;
 	}
 
 	kfree(old_argv);