From 396fba0a59f3c94d6fd6443fbeabd8bd9e3956eb Mon Sep 17 00:00:00 2001 From: "Gustavo A. R. Silva" Date: Thu, 7 May 2020 13:39:09 -0500 Subject: [PATCH] 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") Signed-off-by: Gustavo A. R. Silva Link: https://lore.kernel.org/r/20200507183909.GA12993@embeddedor Signed-off-by: Johannes Berg --- include/linux/ieee80211.h | 6 +++--- include/net/cfg80211.h | 8 ++++---- net/wireless/core.h | 2 +- 3 files changed, 8 insertions(+), 8 deletions(-) diff --git a/include/linux/ieee80211.h b/include/linux/ieee80211.h index 2153d465d752..0320ca4c7d28 100644 --- a/include/linux/ieee80211.h +++ b/include/linux/ieee80211.h @@ -800,7 +800,7 @@ struct ieee80211_msrment_ie { u8 token; u8 mode; u8 type; - u8 request[0]; + u8 request[]; } __packed; /** @@ -1781,7 +1781,7 @@ 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; /** @@ -1793,7 +1793,7 @@ 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; /** diff --git a/include/net/cfg80211.h b/include/net/cfg80211.h index 7415f77d99ca..021366cfb2b0 100644 --- a/include/net/cfg80211.h +++ b/include/net/cfg80211.h @@ -2037,7 +2037,7 @@ 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) @@ -2183,7 +2183,7 @@ struct cfg80211_sched_scan_request { struct list_head list; /* keep last */ - struct ieee80211_channel *channels[0]; + struct ieee80211_channel *channels[]; }; /** @@ -2305,7 +2305,7 @@ struct cfg80211_bss { u8 bssid_index; u8 max_bssid_indicator; - u8 priv[0] __aligned(sizeof(void *)); + u8 priv[] __aligned(sizeof(void *)); }; /** @@ -4852,7 +4852,7 @@ 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) diff --git a/net/wireless/core.h b/net/wireless/core.h index 639d41896573..e0e5b3ee9699 100644 --- a/net/wireless/core.h +++ b/net/wireless/core.h @@ -286,7 +286,7 @@ 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); -- 2.11.0