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cfg80211: Replace zero-length array with flexible-array

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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 7649773293 ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Link: https://lore.kernel.org/r/20200507183909.GA12993@embeddedor
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
This commit is contained in:
Gustavo A. R. Silva 2020-05-07 13:39:09 -05:00 committed by Johannes Berg
parent fedd0fe4e8
commit 396fba0a59
3 changed files with 8 additions and 8 deletions
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6
include/linux/ieee80211.h
View file

@ -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;
/**

8
include/net/cfg80211.h
View file

@ -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)

2
net/wireless/core.h
View file

@ -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);