On Tue, Jun 2, 2020 at 11:34 PM Gustavo A. R. Silva
<gustavoars@xxxxxxxxxx> wrote:
>
> The current codebase makes use of one-element arrays in the following
> form:
>
> struct something {
> int length;
> u8 data[1];
> };
>
> struct something *instance;
>
> instance = kmalloc(sizeof(*instance) + size, GFP_KERNEL);
> instance->length = size;
> memcpy(instance->data, source, size);
>
> but the preferred mechanism to declare variable-length types such as
> these ones is a flexible array member[1][2], introduced in C99:
>
> struct foo {
> int stuff;
> struct boo array[];
> };
>
> By making use of the mechanism above, we will get a compiler warning
> in case the flexible array does not occur last in the structure, which
> will help us prevent some kind of undefined behavior bugs from being
> inadvertently introduced[3] to the codebase from now on.
>
> This issue was found with the help of Coccinelle and audited _manually_.
>
> [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
> [2] https://github.com/KSPP/linux/issues/21
> [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")
>
> Signed-off-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>
Erik, can you take this to the upstream, please?
> ---
> Changes in v2:
> - Don't use struct_size() for now.
> - Update subject line and changelog text.
>
> drivers/acpi/acpica/utids.c | 2 +-
> include/acpi/actypes.h | 2 +-
> 2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/acpi/acpica/utids.c b/drivers/acpi/acpica/utids.c
> index 3bb06935a2ad3..225f3c60203c7 100644
> --- a/drivers/acpi/acpica/utids.c
> +++ b/drivers/acpi/acpica/utids.c
> @@ -263,7 +263,7 @@ acpi_ut_execute_CID(struct acpi_namespace_node *device_node,
> * 3) Size of the actual CID strings
> */
> cid_list_size = sizeof(struct acpi_pnp_device_id_list) +
> - ((count - 1) * sizeof(struct acpi_pnp_device_id)) +
> + count * sizeof(struct acpi_pnp_device_id) +
> string_area_size;
>
> cid_list = ACPI_ALLOCATE_ZEROED(cid_list_size);
> diff --git a/include/acpi/actypes.h b/include/acpi/actypes.h
> index 4defed58ea338..c7bcda0ad366a 100644
> --- a/include/acpi/actypes.h
> +++ b/include/acpi/actypes.h
> @@ -1145,7 +1145,7 @@ struct acpi_pnp_device_id {
> struct acpi_pnp_device_id_list {
> u32 count; /* Number of IDs in Ids array */
> u32 list_size; /* Size of list, including ID strings */
> - struct acpi_pnp_device_id ids[1]; /* ID array */
> + struct acpi_pnp_device_id ids[]; /* ID array */
> };
>
> /*
> --
> 2.27.0
>
