2019-06-10 16:15:50

by Gustavo A. R. Silva

Subject: [PATCH] block: bio: Use struct_size() in kmalloc()

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 bio_map_data {
...
struct iovec iov[];
};

instance = kmalloc(sizeof(sizeof(struct bio_map_data) + sizeof(struct iovec) *
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, iov, count), GFP_KERNEL);

This code was detected with the help of Coccinelle.

Signed-off-by: Gustavo A. R. Silva <[email protected]>
---
block/bio.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/block/bio.c b/block/bio.c
index 683cbb40f051..4bcdcd3f63f4 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -1120,8 +1120,7 @@ static struct bio_map_data *bio_alloc_map_data(struct iov_iter *data,
if (data->nr_segs > UIO_MAXIOV)
return NULL;

- bmd = kmalloc(sizeof(struct bio_map_data) +
- sizeof(struct iovec) * data->nr_segs, gfp_mask);
+ bmd = kmalloc(struct_size(bmd, iov, data->nr_segs), gfp_mask);
if (!bmd)
return NULL;
memcpy(bmd->iov, data->iov, sizeof(struct iovec) * data->nr_segs);
--
2.21.0

2019-06-10 17:53:43

by Kees Cook

Subject: Re: [PATCH] block: bio: Use struct_size() in kmalloc()

On Mon, Jun 10, 2019 at 10:04:12AM -0500, Gustavo A. R. Silva wrote:
> 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 bio_map_data {
> ...
> struct iovec iov[];
> };
>
> instance = kmalloc(sizeof(sizeof(struct bio_map_data) + sizeof(struct iovec) *
> 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, iov, count), GFP_KERNEL);
>
> This code was detected with the help of Coccinelle.
>
> Signed-off-by: Gustavo A. R. Silva <[email protected]>

Reviewed-by: Kees Cook <[email protected]>

-Kees

> ---
> block/bio.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/block/bio.c b/block/bio.c
> index 683cbb40f051..4bcdcd3f63f4 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -1120,8 +1120,7 @@ static struct bio_map_data *bio_alloc_map_data(struct iov_iter *data,
> if (data->nr_segs > UIO_MAXIOV)
> return NULL;
>
> - bmd = kmalloc(sizeof(struct bio_map_data) +
> - sizeof(struct iovec) * data->nr_segs, gfp_mask);
> + bmd = kmalloc(struct_size(bmd, iov, data->nr_segs), gfp_mask);
> if (!bmd)
> return NULL;
> memcpy(bmd->iov, data->iov, sizeof(struct iovec) * data->nr_segs);
> --
> 2.21.0
>

--
Kees Cook

2019-06-15 07:46:30

by Jens Axboe

Subject: Re: [PATCH] block: bio: Use struct_size() in kmalloc()

On 6/10/19 9:04 AM, Gustavo A. R. Silva wrote:
> 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 bio_map_data {
> ...
> struct iovec iov[];
> };
>
> instance = kmalloc(sizeof(sizeof(struct bio_map_data) + sizeof(struct iovec) *
> 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, iov, count), GFP_KERNEL);
>
> This code was detected with the help of Coccinelle.

Applied, thanks.

--
Jens Axboe