[PATCH][next] prism54: Replace zero-length array with flexible-array member

[PATCH][next] prism54: Replace zero-length array with flexible-array member

[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/prism54/isl_oid.h    | 8 ++++----
 drivers/net/wireless/intersil/prism54/islpci_mgt.h | 2 +-
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/net/wireless/intersil/prism54/isl_oid.h b/drivers/net/wireless/intersil/prism54/isl_oid.h
index 5441c1f9f2fc..1afc2ccf94ca 100644
--- a/drivers/net/wireless/intersil/prism54/isl_oid.h
+++ b/drivers/net/wireless/intersil/prism54/isl_oid.h
@@ -37,7 +37,7 @@ struct obj_mlmeex {
 	u16 state;
 	u16 code;
 	u16 size;
-	u8 data[0];
+	u8 data[];
 } __packed;
 
 struct obj_buffer {
@@ -68,12 +68,12 @@ struct obj_bss {
 
 struct obj_bsslist {
 	u32 nr;
-	struct obj_bss bsslist[0];
+	struct obj_bss bsslist[];
 } __packed;
 
 struct obj_frequencies {
 	u16 nr;
-	u16 mhz[0];
+	u16 mhz[];
 } __packed;
 
 struct obj_attachment {
@@ -81,7 +81,7 @@ struct obj_attachment {
 	char reserved;
 	short id;
 	short size;
-	char data[0];
+	char data[];
 } __packed;
 
 /*
diff --git a/drivers/net/wireless/intersil/prism54/islpci_mgt.h b/drivers/net/wireless/intersil/prism54/islpci_mgt.h
index d6bbbac46b4a..1f87d0aea60c 100644
--- a/drivers/net/wireless/intersil/prism54/islpci_mgt.h
+++ b/drivers/net/wireless/intersil/prism54/islpci_mgt.h
@@ -99,7 +99,7 @@ struct islpci_mgmtframe {
 	pimfor_header_t *header;      /* payload header, points into buf */
 	void *data;		      /* payload ex header, points into buf */
         struct work_struct ws;	      /* argument for schedule_work() */
-	char buf[0];		      /* fragment buffer */
+	char buf[];		      /* fragment buffer */
 };
 
 int
-- 
2.25.0

Re: [PATCH][next] prism54: Replace zero-length array with flexible-array member

[Luis Chamberlain]

On Mon, Feb 24, 2020 at 07:20:08PM -0600, Gustavo A. R. Silva 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>

I'd rather we just remove this driver completely, as it has a
replacement upstream p54, and remained upstream just for a theoretical
period of time someone was not able to use p54 anymore. I'll follow up
with a removal of the driver.

  Luis

drivers/net/wireless spring cleaning

[Kalle Valo]

(changing the subject)

Luis Chamberlain <mcgrof@kernel.org> writes:

> On Mon, Feb 24, 2020 at 07:20:08PM -0600, Gustavo A. R. Silva 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>
>
> I'd rather we just remove this driver completely, as it has a
> replacement upstream p54, and remained upstream just for a theoretical
> period of time someone was not able to use p54 anymore. I'll follow up
> with a removal of the driver.

Yeah, please do.

I wonder if we should do other spring cleanup as well and remove drivers
like ray_cs and wl3501, I have not seen any activity on those for years.
Also rndis_wlan would be other candidate for removal.

Anyone know if these drivers are used or if they even work anymore?

-- 
https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches