2024-03-30 17:56:28

by Erick Archer

Subject: [PATCH] mtd: maps: sa1100-flash: Prefer struct_size over open coded arithmetic

This is an effort to get rid of all multiplications from allocation
functions in order to prevent integer overflows [1][2].

As the "info" variable is a pointer to "struct sa_info" and this
structure ends in a flexible array:

struct sa_info {
[...]
struct sa_subdev_info subdev[];
};

the preferred way in the kernel is to use the struct_size() helper to
do the arithmetic instead of the calculation "size + size * count" in
the kzalloc() function.

This way, the code is more readable and safer.

This code was detected with the help of Coccinelle, and audited and
modified manually.

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#open-coded-arithmetic-in-allocator-arguments [1]
Link: https://github.com/KSPP/linux/issues/160 [2]
Signed-off-by: Erick Archer <[email protected]>
---
Hi,

The Coccinelle script used to detect this code pattern is the following:

virtual report

@rule1@
type t1;
type t2;
identifier i0;
identifier i1;
identifier i2;
identifier ALLOC =~ "kmalloc|kzalloc|kmalloc_node|kzalloc_node|vmalloc|vzalloc|kvmalloc|kvzalloc";
position p1;
@@

i0 = sizeof(t1) + sizeof(t2) * i1;
..
i2 = ALLOC@p1(..., i0, ...);

@script:python depends on report@
p1 << rule1.p1;
@@

msg = "WARNING: verify allocation on line %s" % (p1[0].line)
coccilib.report.print_report(p1[0],msg)

Regards,
Erick
---
drivers/mtd/maps/sa1100-flash.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/mtd/maps/sa1100-flash.c b/drivers/mtd/maps/sa1100-flash.c
index d4ce2376d33f..ac8a0a19a021 100644
--- a/drivers/mtd/maps/sa1100-flash.c
+++ b/drivers/mtd/maps/sa1100-flash.c
@@ -153,7 +153,7 @@ static struct sa_info *sa1100_setup_mtd(struct platform_device *pdev,
struct flash_platform_data *plat)
{
struct sa_info *info;
- int nr, size, i, ret = 0;
+ int nr, i, ret = 0;

/*
* Count number of devices.
@@ -167,12 +167,10 @@ static struct sa_info *sa1100_setup_mtd(struct platform_device *pdev,
goto out;
}

- size = sizeof(struct sa_info) + sizeof(struct sa_subdev_info) * nr;
-
/*
* Allocate the map_info structs in one go.
*/
- info = kzalloc(size, GFP_KERNEL);
+ info = kzalloc(struct_size(info, subdev, nr), GFP_KERNEL);
if (!info) {
ret = -ENOMEM;
goto out;
--
2.25.1

2024-04-09 06:41:06

by Miquel Raynal

Subject: Re: [PATCH] mtd: maps: sa1100-flash: Prefer struct_size over open coded arithmetic

On Sat, 2024-03-30 at 17:55:35 UTC, Erick Archer wrote:
> This is an effort to get rid of all multiplications from allocation
> functions in order to prevent integer overflows [1][2].
>
> As the "info" variable is a pointer to "struct sa_info" and this
> structure ends in a flexible array:
>
> struct sa_info {
> [...]
> struct sa_subdev_info subdev[];
> };
>
> the preferred way in the kernel is to use the struct_size() helper to
> do the arithmetic instead of the calculation "size + size * count" in
> the kzalloc() function.
>
> This way, the code is more readable and safer.
>
> This code was detected with the help of Coccinelle, and audited and
> modified manually.
>
> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#open-coded-arithmetic-in-allocator-arguments [1]
> Link: https://github.com/KSPP/linux/issues/160 [2]
> Signed-off-by: Erick Archer <[email protected]>

Applied to https://git.kernel.org/pub/scm/linux/kernel/git/mtd/linux.git mtd/next, thanks.

Miquel