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Date: Fri, 13 Aug 2021 09:08:47 -0700 From: Kees Cook <keescook@...omium.org> To: Johannes Berg <johannes@...solutions.net> Cc: "David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, "Gustavo A. R. Silva" <gustavoars@...nel.org>, Keith Packard <keithpac@...zon.com>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org, linux-wireless@...r.kernel.org, netdev@...r.kernel.org, dri-devel@...ts.freedesktop.org, linux-staging@...ts.linux.dev, linux-block@...r.kernel.org, linux-kbuild@...r.kernel.org, clang-built-linux@...glegroups.com, linux-hardening@...r.kernel.org Subject: Re: [PATCH 39/64] mac80211: Use memset_after() to clear tx status On Fri, Aug 13, 2021 at 09:40:07AM +0200, Johannes Berg wrote: > 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 looks like p54 actually uses the rates, which is why it does this manually. I can't see why carl9170 does this manually, though. > 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); Sounds good; I will adjust these (and drop the BULID_BUG_ONs, as you suggest in the next email). Thanks! -Kees -- Kees Cook
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