| Message ID | 20200507192647.GA16710@embeddedor (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | bd7db3021aa7a31f7d5122af1a863e66c75f88f5 |
| Delegated to: | Kalle Valo |
| Headers | show |
| Series | rndis_wlan: Replace zero-length array with flexible-array | expand |
"Gustavo A. R. Silva" <gustavoars@kernel.org> wrote: > 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 <gustavoars@kernel.org> Patch applied to wireless-drivers-next.git, thanks. bd7db3021aa7 rndis_wlan: Replace zero-length array with flexible-array
diff --git a/drivers/net/wireless/rndis_wlan.c b/drivers/net/wireless/rndis_wlan.c index c8f8fe5497a8..52375f3e430a 100644 --- a/drivers/net/wireless/rndis_wlan.c +++ b/drivers/net/wireless/rndis_wlan.c @@ -201,7 +201,7 @@ struct ndis_80211_pmkid_candidate { struct ndis_80211_pmkid_cand_list { __le32 version; __le32 num_candidates; - struct ndis_80211_pmkid_candidate candidate_list[0]; + struct ndis_80211_pmkid_candidate candidate_list[]; } __packed; struct ndis_80211_status_indication { @@ -246,12 +246,12 @@ struct ndis_80211_bssid_ex { __le32 net_infra; u8 rates[NDIS_802_11_LENGTH_RATES_EX]; __le32 ie_length; - u8 ies[0]; + u8 ies[]; } __packed; struct ndis_80211_bssid_list_ex { __le32 num_items; - struct ndis_80211_bssid_ex bssid[0]; + struct ndis_80211_bssid_ex bssid[]; } __packed; struct ndis_80211_fixed_ies { @@ -333,7 +333,7 @@ struct ndis_80211_bssid_info { struct ndis_80211_pmkid { __le32 length; __le32 bssid_info_count; - struct ndis_80211_bssid_info bssid_info[0]; + struct ndis_80211_bssid_info bssid_info[]; } __packed; /*
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 <gustavoars@kernel.org> --- drivers/net/wireless/rndis_wlan.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)