hostap: 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
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>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200225011151.GA30675@embeddedor

diff --git a/drivers/net/wireless/intersil/hostap/hostap_common.h b/drivers/net/wireless/intersil/hostap/hostap_common.h
index 22543538239b52beb74a66e8d5a961af0e8c5997..dd29a8e8d349614bba37d01ee3de72fb82daa9e5 100644 (file)
--- 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 487883fbb58c0cc63dc6eba318212c23ed2e1841..dd2603d9b5d37de161d95af2f6eaf0e021cbc56f 100644 (file)
--- 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[];
 };