2020-02-11 23:13:10

by Gustavo A. R. Silva

Subject: [PATCH] efi/apple-properties: Replace zero-length array with flexible-array member

The current codebase makes use of the zero-length array language
extension to the C90 standard, 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
inadvertenly introduced[3] to the codebase from now on.

This issue was found with the help of Coccinelle.

[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 <[email protected]>
---
drivers/firmware/efi/apple-properties.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/firmware/efi/apple-properties.c b/drivers/firmware/efi/apple-properties.c
index 0e206c9e0d7a..590c9003f3b4 100644
--- a/drivers/firmware/efi/apple-properties.c
+++ b/drivers/firmware/efi/apple-properties.c
@@ -31,7 +31,7 @@ __setup("dump_apple_properties", dump_properties_enable);
struct dev_header {
u32 len;
u32 prop_count;
- struct efi_dev_path path[0];
+ struct efi_dev_path path[];
/*
* followed by key/value pairs, each key and value preceded by u32 len,
* len includes itself, value may be empty (in which case its len is 4)
@@ -42,7 +42,7 @@ struct properties_header {
u32 len;
u32 version;
u32 dev_count;
- struct dev_header dev_header[0];
+ struct dev_header dev_header[];
};

static void __init unmarshal_key_value_pairs(struct dev_header *dev_header,
--
2.25.0

2020-02-12 07:22:55

by Ard Biesheuvel

Subject: Re: [PATCH] efi/apple-properties: Replace zero-length array with flexible-array member

On Wed, 12 Feb 2020 at 00:11, Gustavo A. R. Silva
<[email protected]> wrote:
>
> The current codebase makes use of the zero-length array language
> extension to the C90 standard, 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
> inadvertenly introduced[3] to the codebase from now on.
>
> This issue was found with the help of Coccinelle.
>
> [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 <[email protected]>

Queued in efi/next

Thanks,

> ---
> drivers/firmware/efi/apple-properties.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/firmware/efi/apple-properties.c b/drivers/firmware/efi/apple-properties.c
> index 0e206c9e0d7a..590c9003f3b4 100644
> --- a/drivers/firmware/efi/apple-properties.c
> +++ b/drivers/firmware/efi/apple-properties.c
> @@ -31,7 +31,7 @@ __setup("dump_apple_properties", dump_properties_enable);
> struct dev_header {
> u32 len;
> u32 prop_count;
> - struct efi_dev_path path[0];
> + struct efi_dev_path path[];
> /*
> * followed by key/value pairs, each key and value preceded by u32 len,
> * len includes itself, value may be empty (in which case its len is 4)
> @@ -42,7 +42,7 @@ struct properties_header {
> u32 len;
> u32 version;
> u32 dev_count;
> - struct dev_header dev_header[0];
> + struct dev_header dev_header[];
> };
>
> static void __init unmarshal_key_value_pairs(struct dev_header *dev_header,
> --
> 2.25.0
>