treewide: Use struct_size() for kmalloc()-family

One of the more common cases of allocation size calculations is finding
the size of a structure that has a zero-sized array at the end, along
with memory for some number of elements for that array. For example:

struct foo {
    int stuff;
    void *entry[];
};

instance = kmalloc(sizeof(struct foo) + sizeof(void *) * count, GFP_KERNEL);

Instead of leaving these open-coded and prone to type mistakes, we can
now use the new struct_size() helper:

instance = kmalloc(struct_size(instance, entry, count), GFP_KERNEL);

This patch makes the changes for kmalloc()-family (and kvmalloc()-family)
uses. It was done via automatic conversion with manual review for the
"CHECKME" non-standard cases noted below, using the following Coccinelle
script:

// pkey_cache = kmalloc(sizeof *pkey_cache + tprops->pkey_tbl_len *
//                      sizeof *pkey_cache->table, GFP_KERNEL);
@@
identifier alloc =~ "kmalloc|kzalloc|kvmalloc|kvzalloc";
expression GFP;
identifier VAR, ELEMENT;
expression COUNT;
@@

- alloc(sizeof(*VAR) + COUNT * sizeof(*VAR->ELEMENT), GFP)
+ alloc(struct_size(VAR, ELEMENT, COUNT), GFP)

// mr = kzalloc(sizeof(*mr) + m * sizeof(mr->map[0]), GFP_KERNEL);
@@
identifier alloc =~ "kmalloc|kzalloc|kvmalloc|kvzalloc";
expression GFP;
identifier VAR, ELEMENT;
expression COUNT;
@@

- alloc(sizeof(*VAR) + COUNT * sizeof(VAR->ELEMENT[0]), GFP)
+ alloc(struct_size(VAR, ELEMENT, COUNT), GFP)

// Same pattern, but can't trivially locate the trailing element name,
// or variable name.
@@
identifier alloc =~ "kmalloc|kzalloc|kvmalloc|kvzalloc";
expression GFP;
expression SOMETHING, COUNT, ELEMENT;
@@

- alloc(sizeof(SOMETHING) + COUNT * sizeof(ELEMENT), GFP)
+ alloc(CHECKME_struct_size(&SOMETHING, ELEMENT, COUNT), GFP)

Signed-off-by: Kees Cook <keescook@chromium.org>

drivers/infiniband/hw/mthca/mthca_memfree.c

@@ -367,7 +367,7 @@ struct mthca_icm_table *mthca_alloc_icm_table(struct mthca_dev *dev,
 	obj_per_chunk = MTHCA_TABLE_CHUNK_SIZE / obj_size;
 	num_icm = DIV_ROUND_UP(nobj, obj_per_chunk);
 
-	table = kmalloc(sizeof *table + num_icm * sizeof *table->icm, GFP_KERNEL);
+	table = kmalloc(struct_size(table, icm, num_icm), GFP_KERNEL);
 	if (!table)
 		return NULL;
 
@@ -529,7 +529,7 @@ struct mthca_user_db_table *mthca_init_user_db_tab(struct mthca_dev *dev)
 		return NULL;
 
 	npages = dev->uar_table.uarc_size / MTHCA_ICM_PAGE_SIZE;
-	db_tab = kmalloc(sizeof *db_tab + npages * sizeof *db_tab->page, GFP_KERNEL);
+	db_tab = kmalloc(struct_size(db_tab, page, npages), GFP_KERNEL);
 	if (!db_tab)
 		return ERR_PTR(-ENOMEM);