| Message ID | 20200225011151.GA30675@embeddedor (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | bc1d50a1a485981784158c62b67c0268fdec5a10 |
| Delegated to: | Kalle Valo |
| Headers | show |
| Series | [next] hostap: Replace zero-length array with flexible-array member | expand |
"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
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[]; };
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(-)