[PATCH][next] staging: wlan-ng: Replace one-element arrays with flexible-array members

[PATCH][next] staging: wlan-ng: Replace one-element arrays with flexible-array members

[Gustavo A. R. Silva]

There is a regular need in the kernel to provide a way to declare having
a dynamically sized set of trailing elements in a structure. Kernel code
should always use “flexible array members”[1] for these cases. The older
style of one-element or zero-length arrays should no longer be used[2].

This helps with the ongoing efforts to globally enable -Warray-bounds
and get us closer to being able to tighten the FORTIFY_SOURCE routines
on memcpy().

This issue was found with the help of Coccinelle and audited and fixed,
manually.

[1] https://en.wikipedia.org/wiki/Flexible_array_member
[2] https://www.kernel.org/doc/html/v5.16/process/deprecated.html#zero-length-and-one-element-arrays

Link: https://github.com/KSPP/linux/issues/79
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
 drivers/staging/wlan-ng/p80211mgmt.h  | 8 ++++----
 drivers/staging/wlan-ng/p80211types.h | 2 +-
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/staging/wlan-ng/p80211mgmt.h b/drivers/staging/wlan-ng/p80211mgmt.h
index 1ef30d3f3159..d6fe52de2c8f 100644
--- a/drivers/staging/wlan-ng/p80211mgmt.h
+++ b/drivers/staging/wlan-ng/p80211mgmt.h
@@ -229,14 +229,14 @@ struct wlan_ie {
 struct wlan_ie_ssid {
 	u8 eid;
 	u8 len;
-	u8 ssid[1];		/* may be zero, ptrs may overlap */
+	u8 ssid[];		/* may be zero, ptrs may overlap */
 } __packed;
 
 /*-- Supported Rates  -----------------------------*/
 struct wlan_ie_supp_rates {
 	u8 eid;
 	u8 len;
-	u8 rates[1];		/* had better be at LEAST one! */
+	u8 rates[];		/* had better be at LEAST one! */
 } __packed;
 
 /*-- FH Parameter Set  ----------------------------*/
@@ -274,7 +274,7 @@ struct wlan_ie_tim {
 	u8 dtim_cnt;
 	u8 dtim_period;
 	u8 bitmap_ctl;
-	u8 virt_bm[1];
+	u8 virt_bm[];
 } __packed;
 
 /*-- IBSS Parameter Set ---------------------------*/
@@ -288,7 +288,7 @@ struct wlan_ie_ibss_parms {
 struct wlan_ie_challenge {
 	u8 eid;
 	u8 len;
-	u8 challenge[1];
+	u8 challenge[];
 } __packed;
 
 /*-------------------------------------------------*/
diff --git a/drivers/staging/wlan-ng/p80211types.h b/drivers/staging/wlan-ng/p80211types.h
index 6486612a8f31..b2ffd09881b0 100644
--- a/drivers/staging/wlan-ng/p80211types.h
+++ b/drivers/staging/wlan-ng/p80211types.h
@@ -234,7 +234,7 @@ struct p80211pstr32 {
 /* MAC address array */
 struct p80211macarray {
 	u32 cnt;
-	u8 data[1][MAXLEN_PSTR6];
+	u8 data[][MAXLEN_PSTR6];
 } __packed;
 
 /* prototype template */
-- 
2.27.0

Re: [PATCH][next] staging: wlan-ng: Replace one-element arrays with flexible-array members

[Dan Carpenter]

On Fri, Feb 04, 2022 at 05:30:15PM -0600, Gustavo A. R. Silva wrote:
> There is a regular need in the kernel to provide a way to declare having
> a dynamically sized set of trailing elements in a structure. Kernel code
> should always use “flexible array members”[1] for these cases. The older
> style of one-element or zero-length arrays should no longer be used[2].
> 
> This helps with the ongoing efforts to globally enable -Warray-bounds
> and get us closer to being able to tighten the FORTIFY_SOURCE routines
> on memcpy().
> 
> This issue was found with the help of Coccinelle and audited and fixed,
> manually.

How are you auditing this manually?  I have to re-audit it manually
myself as a reviewer and I'm find it tricky.

>  /*-- IBSS Parameter Set ---------------------------*/
> @@ -288,7 +288,7 @@ struct wlan_ie_ibss_parms {
>  struct wlan_ie_challenge {
>  	u8 eid;
>  	u8 len;
> -	u8 challenge[1];
> +	u8 challenge[];
>  } __packed;

This is dead code.  It would have been better to just delete that.  I
have a lot of experience at reviewing "Delete Dead Code" patches.

regards,
dan carpenter