staging: r8188eu: Fix warning of array overflow in ioctl_linux.c

Building with -Warray-bounds results in the following warning plus others
related to the same problem:

CC [M]  drivers/staging/r8188eu/os_dep/ioctl_linux.o
In function ‘wpa_set_encryption’,
    inlined from ‘rtw_wx_set_enc_ext’ at drivers/staging/r8188eu/os_dep/ioctl_linux.c:1868:9:
drivers/staging/r8188eu/os_dep/ioctl_linux.c:412:41: warning: array subscript ‘struct ndis_802_11_wep[0]’ is partly outside array bounds of ‘void[25]’ [-Warray-bounds]
  412 |                         pwep->KeyLength = wep_key_len;
      |                         ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~
In file included from drivers/staging/r8188eu/os_dep/../include/osdep_service.h:19,
                 from drivers/staging/r8188eu/os_dep/ioctl_linux.c:4:
In function ‘kmalloc’,
    inlined from ‘kzalloc’ at ./include/linux/slab.h:733:9,
    inlined from ‘wpa_set_encryption’ at drivers/staging/r8188eu/os_dep/ioctl_linux.c:408:11,
    inlined from ‘rtw_wx_set_enc_ext’ at drivers/staging/r8188eu/os_dep/ioctl_linux.c:1868:9:
./include/linux/slab.h:605:16: note: object of size [17, 25] allocated by ‘__kmalloc’
  605 |         return __kmalloc(size, flags);
      |                ^~~~~~~~~~~~~~~~~~~~~~
./include/linux/slab.h:600:24: note: object of size [17, 25] allocated by ‘kmem_cache_alloc_trace’
  600 |                 return kmem_cache_alloc_trace(
      |                        ^~~~~~~~~~~~~~~~~~~~~~~
  601 |                                 kmalloc_caches[kmalloc_type(flags)][index],
      |                                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  602 |                                 flags, size);
      |                                 ~~~~~~~~~~~~

Although it is unlikely that anyone is still using WEP encryption, the
size of the allocation needs to be increased just in case.

Fixes commit 2b42bd58b3 ("staging: r8188eu: introduce new os_dep dir for RTL8188eu driver")

Fixes: 2b42bd58b3 ("staging: r8188eu: introduce new os_dep dir for RTL8188eu driver")
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Cc: Phillip Potter <phil@philpotter.co.uk>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/r/20220531013103.2175-3-Larry.Finger@lwfinger.net
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/r8188eu/os_dep/ioctl_linux.c

@@ -403,7 +403,7 @@ static int wpa_set_encryption(struct net_device *dev, struct ieee_param *param,
 
 		if (wep_key_len > 0) {
 			wep_key_len = wep_key_len <= 5 ? 5 : 13;
-			wep_total_len = wep_key_len + FIELD_OFFSET(struct ndis_802_11_wep, KeyMaterial);
+			wep_total_len = wep_key_len + sizeof(*pwep);
 			pwep = kzalloc(wep_total_len, GFP_KERNEL);
 			if (!pwep)
 				goto exit;