RE: [PATCH v2] ACPICA: Replace one-element array with flexible-array

[Kaneda, Erik]

> -----Original Message-----
> From: linux-acpi-owner@xxxxxxxxxxxxxxx <linux-acpi-
> owner@xxxxxxxxxxxxxxx> On Behalf Of Rafael J. Wysocki
> Sent: Wednesday, June 3, 2020 6:04 AM
> To: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>; Kaneda, Erik
> <erik.kaneda@xxxxxxxxx>
> Cc: Moore, Robert <robert.moore@xxxxxxxxx>; Wysocki, Rafael J
> <rafael.j.wysocki@xxxxxxxxx>; Len Brown <lenb@xxxxxxxxxx>; ACPI Devel
> Maling List <linux-acpi@xxxxxxxxxxxxxxx>; open list:ACPI COMPONENT
> ARCHITECTURE (ACPICA) <devel@xxxxxxxxxx>; Linux Kernel Mailing List
> <linux-kernel@xxxxxxxxxxxxxxx>; Gustavo A. R. Silva
> <gustavo@xxxxxxxxxxxxxx>
> Subject: Re: [PATCH v2] ACPICA: Replace one-element array with flexible-
> array
> 
> 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?
Yes, We'll have to make additional changes to other structures with one-element arrays but we'll get this in time for the upcoming ACPICA release.

Thanks,
Erik
> 
> > ---
> > 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
> >