On Sat, 2021-07-31 at 08:55 -0700, Kees Cook wrote:
On Tue, Jul 27, 2021 at 01:58:30PM -0700, Kees Cook wrote:
In preparation for FORTIFY_SOURCE performing compile-time and run-time field bounds checking for memset(), avoid intentionally writing across neighboring fields.
Use memset_after() so memset() doesn't get confused about writing beyond the destination member that is intended to be the starting point of zeroing through the end of the struct.
Note that the common helper, ieee80211_tx_info_clear_status(), does NOT clear ack_signal, but the open-coded versions do. All three perform checks that the ack_signal position hasn't changed, though.
Quick ping on this question: there is a mismatch between the common helper and the other places that do this. Is there a bug here?
Yes.
The common helper should also clear ack_signal, but that was broken by commit e3e1a0bcb3f1 ("mac80211: reduce IEEE80211_TX_MAX_RATES"), because that commit changed the order of the fields and updated carl9170 and p54 properly but not the common helper...
It doesn't actually matter much because ack_signal is normally filled in afterwards, and even if it isn't, it's just for statistics.
The correct thing to do here would be to
memset_after(&info->status, 0, rates);
johannes