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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id n22sm1014921pff.57.2021.07.28.14.54.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 28 Jul 2021 14:54:53 -0700 (PDT) Date: Wed, 28 Jul 2021 14:54:52 -0700 From: Kees Cook To: dsterba@suse.cz, Dan Carpenter , linux-hardening@vger.kernel.org, "Gustavo A. R. Silva" , Keith Packard , Greg Kroah-Hartman , Andrew Morton , linux-kernel@vger.kernel.org, linux-wireless@vger.kernel.org, netdev@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-staging@lists.linux.dev, linux-block@vger.kernel.org, linux-kbuild@vger.kernel.org, clang-built-linux@googlegroups.com Subject: Re: [PATCH 02/64] mac80211: Use flex-array for radiotap header bitmap Message-ID: <202107281454.F96505E15@keescook> References: <20210727205855.411487-1-keescook@chromium.org> <20210727205855.411487-3-keescook@chromium.org> <20210728073556.GP1931@kadam> <20210728092323.GW5047@twin.jikos.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210728092323.GW5047@twin.jikos.cz> Precedence: bulk List-ID: X-Mailing-List: linux-wireless@vger.kernel.org On Wed, Jul 28, 2021 at 11:23:23AM +0200, David Sterba wrote: > On Wed, Jul 28, 2021 at 10:35:56AM +0300, Dan Carpenter wrote: > > @@ -372,7 +372,7 @@ ieee80211_add_rx_radiotap_header(struct ieee80211_local *local, > > ieee80211_calculate_rx_timestamp(local, status, > > mpdulen, 0), > > pos); > > - rthdr->it_present |= cpu_to_le32(1 << IEEE80211_RADIOTAP_TSFT); > > + rthdr->data.it_present |= cpu_to_le32(1 << IEEE80211_RADIOTAP_TSFT); > > A drive-by comment, not related to the patchset, but rather the > ieee80211 driver itself. > > Shift expressions with (1 << NUMBER) can be subtly broken once the > NUMBER is 31 and the value gets silently cast to a 64bit type. It will > become 0xfffffffff80000000. > > I've checked the IEEE80211_RADIOTAP_* defintions if this is even remotely > possible and yes, IEEE80211_RADIOTAP_EXT == 31. Fortunatelly it seems to > be used with used with a 32bit types (eg. _bitmap_shifter) so there are > no surprises. > > The recommended practice is to always use unsigned types for shifts, so > "1U << ..." at least. Ah, good catch! I think just using BIT() is the right replacement here, yes? I suppose that should be a separate patch. -- Kees Cook