Re: [PATCH][next] staging: rtl8723bs: Replace one-element array with flexible-array member in struct ndis_80211_var_ie

[Dan Carpenter]

On Wed, Feb 10, 2021 at 04:49:37PM -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].
> 
> Refactor the code according to the use of a flexible-array member in
> struct ndis_80211_var_ie, instead of a one-element array.
> 
> Also, this helps with the ongoing efforts to enable -Warray-bounds and
> fix the following warnings:
> 
>   CC [M]  drivers/staging/rtl8723bs/core/rtw_wlan_util.o
> In file included from ./drivers/staging/rtl8723bs/include/drv_types.h:20,
>                  from drivers/staging/rtl8723bs/core/rtw_wlan_util.c:9:
> drivers/staging/rtl8723bs/core/rtw_wlan_util.c: In function ‘HT_caps_handler’:
> ./drivers/staging/rtl8723bs/include/basic_types.h:108:11: warning: array subscript 1 is above array bounds of ‘u8[1]’ {aka ‘unsigned char[1]’} [-Warray-bounds]
>   108 |  (EF1BYTE(*((u8 *)(__pstart))))
>       |           ^
> ./drivers/staging/rtl8723bs/include/basic_types.h:42:8: note: in definition of macro ‘EF1BYTE’
>    42 |  ((u8)(_val))
>       |        ^~~~
> ./drivers/staging/rtl8723bs/include/basic_types.h:127:4: note: in expansion of macro ‘LE_P1BYTE_TO_HOST_1BYTE’
>   127 |   (LE_P1BYTE_TO_HOST_1BYTE(__pstart) >> (__bitoffset)) & \
>       |    ^~~~~~~~~~~~~~~~~~~~~~~
> ./drivers/staging/rtl8723bs/include/rtw_ht.h:97:55: note: in expansion of macro ‘LE_BITS_TO_1BYTE’
>    97 | #define GET_HT_CAPABILITY_ELE_RX_STBC(_pEleStart)     LE_BITS_TO_1BYTE((_pEleStart)+1, 0, 2)
>       |                                                       ^~~~~~~~~~~~~~~~
> drivers/staging/rtl8723bs/core/rtw_wlan_util.c:1104:58: note: in expansion of macro ‘GET_HT_CAPABILITY_ELE_RX_STBC’
>  1104 |   if (TEST_FLAG(phtpriv->stbc_cap, STBC_HT_ENABLE_TX) && GET_HT_CAPABILITY_ELE_RX_STBC(pIE->data)) {
>       |                                                          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/staging/rtl8723bs/core/rtw_wlan_util.c:1051:75: warning: array subscript 2 is above array bounds of ‘u8[1]’ {aka ‘unsigned char[1]’} [-Warray-bounds]
>  1051 |    if ((pmlmeinfo->HT_caps.u.HT_cap_element.AMPDU_para & 0x3) > (pIE->data[i] & 0x3))
>       |                                                                  ~~~~~~~~~^~~
> drivers/staging/rtl8723bs/core/rtw_wlan_util.c: In function ‘check_assoc_AP’:
> drivers/staging/rtl8723bs/core/rtw_wlan_util.c:1606:19: warning: array subscript 4 is above array bounds of ‘u8[1]’ {aka ‘unsigned char[1]’} [-Warray-bounds]
>  1606 |      if (pIE->data[4] == 1)
>       |          ~~~~~~~~~^~~
> drivers/staging/rtl8723bs/core/rtw_wlan_util.c:1609:20: warning: array subscript 5 is above array bounds of ‘u8[1]’ {aka ‘unsigned char[1]’} [-Warray-bounds]
>  1609 |       if (pIE->data[5] & RT_HT_CAP_USE_92SE)
>       |           ~~~~~~~~~^~~
> drivers/staging/rtl8723bs/core/rtw_wlan_util.c:1613:19: warning: array subscript 5 is above array bounds of ‘u8[1]’ {aka ‘unsigned char[1]’} [-Warray-bounds]
>  1613 |      if (pIE->data[5] & RT_HT_CAP_USE_SOFTAP)
>       |          ~~~~~~~~~^~~
> drivers/staging/rtl8723bs/core/rtw_wlan_util.c:1617:20: warning: array subscript 6 is above array bounds of ‘u8[1]’ {aka ‘unsigned char[1]’} [-Warray-bounds]
>  1617 |       if (pIE->data[6] & RT_HT_CAP_USE_JAGUAR_BCUT) {
>       |           ~~~~~~~~~^~~
> 
> [1] https://en.wikipedia.org/wiki/Flexible_array_member
> [2] https://www.kernel.org/doc/html/v5.9/process/deprecated.html#zero-length-and-one-element-arrays
> 
> Link: https://github.com/KSPP/linux/issues/79
> Link: https://github.com/KSPP/linux/issues/109
> Build-tested-by: kernel test robot <lkp@xxxxxxxxx>
> Link: https://lore.kernel.org/lkml/602434b8.jc5DoXJ0bmHoxgIL%25lkp@xxxxxxxxx/
> Signed-off-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>

Looks okay to me.  I looked for potential issues with changing the
sizeof the struct but couldn't find any.

Reviewed-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>

regards,
dan carpenter