[PATCH v2] kernel: module: Use struct_size() helper

[PATCH v2] kernel: module: Use struct_size() helper

[Gustavo A. R. Silva]

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 module_sect_attrs {
	...
        struct module_sect_attr attrs[0];
};

Make use of the struct_size() helper instead of an open-coded version
in order to avoid any potential type mistakes.

So, replace the following form:

sizeof(*sect_attrs) + nloaded * sizeof(sect_attrs->attrs[0]

with:

struct_size(sect_attrs, attrs, nloaded)

This code was detected with the help of Coccinelle.

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
---
Changes in v2:
 - Update changelog text by adding a better description for
   the motivation and usage of the struct_size() helper.

 kernel/module.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/kernel/module.c b/kernel/module.c
index 80c7c09584cf..3f3bb090fbf4 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -1492,8 +1492,7 @@ static void add_sect_attrs(struct module *mod, const struct load_info *info)
 	for (i = 0; i < info->hdr->e_shnum; i++)
 		if (!sect_empty(&info->sechdrs[i]))
 			nloaded++;
-	size[0] = ALIGN(sizeof(*sect_attrs)
-			+ nloaded * sizeof(sect_attrs->attrs[0]),
+	size[0] = ALIGN(struct_size(sect_attrs, attrs, nloaded),
 			sizeof(sect_attrs->grp.attrs[0]));
 	size[1] = (nloaded + 1) * sizeof(sect_attrs->grp.attrs[0]);
 	sect_attrs = kzalloc(size[0] + size[1], GFP_KERNEL);
-- 
2.21.0

Re: [PATCH v2] kernel: module: Use struct_size() helper

[Jessica Yu]

+++ Gustavo A. R. Silva [06/06/19 13:18 -0500]:
>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 module_sect_attrs {
>	...
>        struct module_sect_attr attrs[0];
>};
>
>Make use of the struct_size() helper instead of an open-coded version
>in order to avoid any potential type mistakes.
>
>So, replace the following form:
>
>sizeof(*sect_attrs) + nloaded * sizeof(sect_attrs->attrs[0]
>
>with:
>
>struct_size(sect_attrs, attrs, nloaded)
>
>This code was detected with the help of Coccinelle.
>
>Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
>---
>Changes in v2:
> - Update changelog text by adding a better description for
>   the motivation and usage of the struct_size() helper.

Applied. Thanks a lot!

Jessica