Re: [PATCH] mwifiex: Avoid memset() over-write of WEP key_material

On Thu, Jun 17, 2021 at 10:15 AM Kees Cook [off-list ref] wrote:

In preparation for FORTIFY_SOURCE performing compile-time and run-time
field bounds checking for memset(), avoid intentionally writing across
neighboring array fields.

When preparing to call mwifiex_set_keyparamset_wep(), key_material is
treated very differently from its structure layout (which has only a
single struct mwifiex_ie_type_key_param_set). Instead, add a new type to
the union so memset() can correctly reason about the size of the
structure.

Note that the union ("params", 196 bytes) containing key_material was
not large enough to hold the target of this memset(): sizeof(struct
mwifiex_ie_type_key_param_set) == 60, NUM_WEP_KEYS = 4, so 240
bytes, or 44 bytes past the end of "params". The good news is that
it appears that the command buffer, as allocated, is 2048 bytes
(MWIFIEX_SIZE_OF_CMD_BUFFER), so no neighboring memory appears to be
getting clobbered.

Yeah, this union vs. the underlying buffer size always throws me for a
loop on figuring out whether there's truly a buffer overflow on some
of this stuff...

Signed-off-by: Kees Cook <redacted>

Looks like a valid refactor to me:

Reviewed-by: Brian Norris <briannorris@chromium.org>