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

From: Gustavo A. R. Silva
Date: Mon Jun 10 2019 - 11:08:40 EST

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 <gustavo@xxxxxxxxxxxxxx>
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);