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prism54: Replace zero-length array with flexible-array member

PATCH In review Gustavo A. R. Silva 3 participants 3 messages Feb 25, 2020 – Mar 23, 2020

Subsystems (3)
Networking Network drivers P54 wireless driver
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Gustavo A. R. Silva

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#0 lore raw

PATCH 1/1 prism54: 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 <[email protected]>
---
 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(-)
drivers/net/wireless/intersil/prism54/isl_oid.h +4 -4
index 5441c1f9f2fc..1afc2ccf94ca 100644
@@ -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;
 
 /*
drivers/net/wireless/intersil/prism54/islpci_mgt.h +1 -1
index d6bbbac46b4a..1f87d0aea60c 100644
@@ -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
Signature · 1 line
2.25.0
#1 lore raw
Quoted 22 lines · 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]

Quoted 7 lines

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]>

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

#2 lore raw

drivers/net/wireless spring cleaning

(changing the subject)

Quoted 29 lines · Luis Chamberlain
Quoted 28 lines · 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")

Quoted 6 lines
Quoted 1 line
Signed-off-by Gustavo A. R. Silva <[email protected]>

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?

Signature · 1 line
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