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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id nl2sm714675pjb.10.2021.07.29.23.06.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 29 Jul 2021 23:06:26 -0700 (PDT) Date: Thu, 29 Jul 2021 23:06:25 -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: <202107292305.DB86BAC@keescook> References: <20210727205855.411487-1-keescook@chromium.org> <20210727205855.411487-3-keescook@chromium.org> <20210728073556.GP1931@kadam> <20210728092323.GW5047@twin.jikos.cz> <202107281454.F96505E15@keescook> <20210729104547.GT5047@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210729104547.GT5047@suse.cz> Precedence: bulk List-ID: X-Mailing-List: linux-wireless@vger.kernel.org On Thu, Jul 29, 2021 at 12:45:47PM +0200, David Sterba wrote: > On Wed, Jul 28, 2021 at 02:54:52PM -0700, Kees Cook wrote: > > 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. > > I found definition of BIT in vdso/bits.h, that does not sound like a > standard header, besides that it shifts 1UL, that may not be necessary > everywhere. IIRC there were objections against using the macro at all. 3945ff37d2f4 ("linux/bits.h: Extract common header for vDSO") moved it there from linux/bits.h, and linux/bits.h now includes vdso/bits.h, so it is still ever-present. :) -- Kees Cook