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>

3 files changed, 4 insertions, 6 deletions

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index a662bfcbea0e..2238661bf878 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -4775,8 +4775,8 @@ static struct cgroup *cgroup_create(struct cgroup *parent)
 	int ret;
 
 	/* allocate the cgroup and its ID, 0 is reserved for the root */
-	cgrp = kzalloc(sizeof(*cgrp) +
-		       sizeof(cgrp->ancestor_ids[0]) * (level + 1), GFP_KERNEL);
+	cgrp = kzalloc(struct_size(cgrp, ancestor_ids, (level + 1)),
+		       GFP_KERNEL);
 	if (!cgrp)
 		return ERR_PTR(-ENOMEM);
 
diff --git a/kernel/module.c b/kernel/module.c
index ce8066b88178..307272679a55 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -1604,8 +1604,7 @@ static void add_notes_attrs(struct module *mod, const struct load_info *info)
 	if (notes == 0)
 		return;
 
-	notes_attrs = kzalloc(sizeof(*notes_attrs)
-			      + notes * sizeof(notes_attrs->attrs[0]),
+	notes_attrs = kzalloc(struct_size(notes_attrs, attrs, notes),
 			      GFP_KERNEL);
 	if (notes_attrs == NULL)
 		return;
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index ca7959be8aaa..c976e2bfbac5 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -3700,8 +3700,7 @@ apply_wqattrs_prepare(struct workqueue_struct *wq,
 
 	lockdep_assert_held(&wq_pool_mutex);
 
-	ctx = kzalloc(sizeof(*ctx) + nr_node_ids * sizeof(ctx->pwq_tbl[0]),
-		      GFP_KERNEL);
+	ctx = kzalloc(struct_size(ctx, pwq_tbl, nr_node_ids), GFP_KERNEL);
 
 	new_attrs = alloc_workqueue_attrs(GFP_KERNEL);
 	tmp_attrs = alloc_workqueue_attrs(GFP_KERNEL);