cfg80211: Replace zero-length array with flexible-array
PATCH 1/1 cfg80211: Replace zero-length array with flexible-array
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]
sizeof(flexible-array-member) triggers a warning because flexible array members have incomplete type[1]. There are some instances of code in which the sizeof operator is being incorrectly/erroneously applied to zero-length arrays and the result is zero. Such instances may be hiding some bugs. So, this work (flexible-array member conversions) will also help to get completely rid of those sorts of issues.
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")
--- include/linux/ieee80211.h | 6 +++--- include/net/cfg80211.h | 8 ++++---- net/wireless/core.h | 2 +- 3 files changed, 8 insertions(+), 8 deletions(-)
include/linux/ieee80211.h +3 -3
@@ -716,7 +716,7 @@ struct ieee80211_msrment_ie {u8 token;u8 mode;u8 type; -u8 request[0 ]; +u8 request[]; } __packed;/**
@@ -1641,7 +1641,7 @@ struct ieee80211_he_operation {__le32 he_oper_params;__le16 he_mcs_nss_set;/* Optional 0,1,3,4,5,7 or 8 bytes: depends on @he_oper_params */ -u8 optional[0 ]; +u8 optional[]; } __packed;/**
@@ -1653,7 +1653,7 @@ struct ieee80211_he_operation {struct ieee80211_he_spr {u8 he_sr_control;/* Optional 0 to 19 bytes: depends on @he_sr_control */ -u8 optional[0 ]; +u8 optional[]; } __packed;/**
include/net/cfg80211.h +4 -4
@@ -2029,7 +2029,7 @@ struct cfg80211_scan_request {bool no_cck;/* keep last */ -struct ieee80211_channel *channels[0 ]; +struct ieee80211_channel *channels[]; };static inline void get_random_mask_addr (u8 *buf,const u8 *addr,const u8 *mask)
@@ -2175,7 +2175,7 @@ struct cfg80211_sched_scan_request {struct list_head list;/* keep last */ -struct ieee80211_channel *channels[0 ]; +struct ieee80211_channel *channels[]; };/**
@@ -2297,7 +2297,7 @@ struct cfg80211_bss {u8 bssid_index;u8 max_bssid_indicator; -u8 priv[0 ]__aligned(sizeof(void *)) ; +u8 priv[]__aligned(sizeof(void *)) ; };/**
@@ -4829,7 +4829,7 @@ struct wiphy {u8 max_data_retry_count; -char priv[0 ]__aligned(NETDEV_ALIGN) ; +char priv[]__aligned(NETDEV_ALIGN) ; };static inline struct net *wiphy_net (struct wiphy *wiphy)
net/wireless/core.h +1 -1
@@ -290,7 +290,7 @@ struct cfg80211_cqm_config {u32 rssi_hyst;s32 last_rssi_event_value;int n_rssi_thresholds; -s32 rssi_thresholds[0 ]; +s32 rssi_thresholds[]; };void cfg80211_destroy_ifaces (struct cfg80211_registered_device *rdev);