* [PATCH][next] hostap: Replace zero-length array with flexible-array member
@ 2020-02-25 1:11 Gustavo A. R. Silva
2020-03-23 16:59 ` Kalle Valo
0 siblings, 1 reply; 2+ messages in thread
From: Gustavo A. R. Silva @ 2020-02-25 1:11 UTC (permalink / raw)
To: Jouni Malinen, Kalle Valo, David S. Miller
Cc: linux-wireless, netdev, linux-kernel, Gustavo A. R. Silva
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
inadvertently introduced[3] to the codebase from now on.
Also, notice that, dynamic memory allocations won't be affected by
this change:
"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]
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 <gustavo@embeddedor.com>
---
drivers/net/wireless/intersil/hostap/hostap_common.h | 2 +-
drivers/net/wireless/intersil/hostap/hostap_wlan.h | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/net/wireless/intersil/hostap/hostap_common.h b/drivers/net/wireless/intersil/hostap/hostap_common.h
index 22543538239b..dd29a8e8d349 100644
--- a/drivers/net/wireless/intersil/hostap/hostap_common.h
+++ b/drivers/net/wireless/intersil/hostap/hostap_common.h
@@ -322,7 +322,7 @@ struct prism2_download_param {
u32 addr; /* wlan card address */
u32 len;
void __user *ptr; /* pointer to data in user space */
- } data[0];
+ } data[];
};
#define PRISM2_MAX_DOWNLOAD_AREA_LEN 131072
diff --git a/drivers/net/wireless/intersil/hostap/hostap_wlan.h b/drivers/net/wireless/intersil/hostap/hostap_wlan.h
index 487883fbb58c..dd2603d9b5d3 100644
--- a/drivers/net/wireless/intersil/hostap/hostap_wlan.h
+++ b/drivers/net/wireless/intersil/hostap/hostap_wlan.h
@@ -615,7 +615,7 @@ struct prism2_download_data {
u32 addr; /* wlan card address */
u32 len;
u8 *data; /* allocated data */
- } data[0];
+ } data[];
};
--
2.25.0
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH][next] hostap: Replace zero-length array with flexible-array member
2020-02-25 1:11 [PATCH][next] hostap: Replace zero-length array with flexible-array member Gustavo A. R. Silva
@ 2020-03-23 16:59 ` Kalle Valo
0 siblings, 0 replies; 2+ messages in thread
From: Kalle Valo @ 2020-03-23 16:59 UTC (permalink / raw)
To: Gustavo A. R. Silva
Cc: Jouni Malinen, David S. Miller, linux-wireless, netdev,
linux-kernel, Gustavo A. R. Silva
"Gustavo A. R. Silva" <gustavo@embeddedor.com> 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
> inadvertently introduced[3] to the codebase from now on.
>
> Also, notice that, dynamic memory allocations won't be affected by
> this change:
>
> "Flexible array members have incomplete type, and so the sizeof operator
> may not be applied. As a quirk of the original implementation of
> zero-length arrays, sizeof evaluates to zero."[1]
>
> 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 <gustavo@embeddedor.com>
Patch applied to wireless-drivers-next.git, thanks.
bc1d50a1a485 hostap: Replace zero-length array with flexible-array member
--
https://patchwork.kernel.org/patch/11402357/
https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches
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