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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id m34sm1068670pgb.85.2021.07.28.16.33.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 28 Jul 2021 16:33:20 -0700 (PDT) Date: Wed, 28 Jul 2021 16:33:18 -0700 From: Kees Cook To: Dan Carpenter Cc: 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: <202107281630.B0519DA@keescook> References: <20210727205855.411487-1-keescook@chromium.org> <20210727205855.411487-3-keescook@chromium.org> <20210728073556.GP1931@kadam> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210728073556.GP1931@kadam> Precedence: bulk List-ID: X-Mailing-List: linux-hardening@vger.kernel.org On Wed, Jul 28, 2021 at 10:35:56AM +0300, Dan Carpenter wrote: > On Tue, Jul 27, 2021 at 01:57:53PM -0700, Kees Cook wrote: > > [...] > > - /** > > - * @it_present: (first) present word > > - */ > > - __le32 it_present; > > + union { > > + /** > > + * @it_present: (first) present word > > + */ > > + __le32 it_present; > > + > > + struct { > > + /* The compiler makes it difficult to overlap > > + * a flex-array with an existing singleton, > > + * so we're forced to add an empty named > > + * variable here. > > + */ > > + struct { } __unused; > > + > > + /** > > + * @bitmap: all presence bitmaps > > + */ > > + __le32 bitmap[]; > > + }; > > + }; > > } __packed; > > This patch is so confusing... > > Btw, after the end of the __le32 data there is a bunch of other le64, > u8 and le16 data so the struct is not accurate or complete. > > It might be better to re-write this as something like this: > > diff --git a/include/net/ieee80211_radiotap.h b/include/net/ieee80211_radiotap.h > index c0854933e24f..0cb5719e9668 100644 > --- a/include/net/ieee80211_radiotap.h > +++ b/include/net/ieee80211_radiotap.h > @@ -42,7 +42,10 @@ struct ieee80211_radiotap_header { > /** > * @it_present: (first) present word > */ > - __le32 it_present; > + struct { > + __le32 it_present; > + char buff[]; > + } data; > } __packed; Ah-ha, got it: diff --git a/include/net/ieee80211_radiotap.h b/include/net/ieee80211_radiotap.h index c0854933e24f..6b7274edb3c6 100644 --- a/include/net/ieee80211_radiotap.h +++ b/include/net/ieee80211_radiotap.h @@ -43,6 +43,10 @@ struct ieee80211_radiotap_header { * @it_present: (first) present word */ __le32 it_present; + /** + * @it_optional: all remaining presence bitmaps + */ + __le32 it_optional[]; } __packed; /* version is always 0 */ diff --git a/net/mac80211/rx.c b/net/mac80211/rx.c index 2563473b5cf1..b6a960d37278 100644 --- a/net/mac80211/rx.c +++ b/net/mac80211/rx.c @@ -359,7 +359,13 @@ ieee80211_add_rx_radiotap_header(struct ieee80211_local *local, put_unaligned_le32(it_present_val, it_present); - pos = (void *)(it_present + 1); + /* + * This references through an offset into it_optional[] rather + * than via it_present otherwise later uses of pos will cause + * the compiler to think we have walked past the end of the + * struct member. + */ + pos = (void *)&rthdr->it_optional[it_present - rthdr->it_optional]; /* the order of the following fields is important */ diff --git a/net/wireless/radiotap.c b/net/wireless/radiotap.c index 36f1b59a78bf..081f0a3bdfe1 100644 --- a/net/wireless/radiotap.c +++ b/net/wireless/radiotap.c @@ -115,10 +115,9 @@ int ieee80211_radiotap_iterator_init( iterator->_max_length = get_unaligned_le16(&radiotap_header->it_len); iterator->_arg_index = 0; iterator->_bitmap_shifter = get_unaligned_le32(&radiotap_header->it_present); - iterator->_arg = (uint8_t *)radiotap_header + sizeof(*radiotap_header); + iterator->_arg = (uint8_t *)radiotap_header->it_optional; iterator->_reset_on_ext = 0; - iterator->_next_bitmap = &radiotap_header->it_present; - iterator->_next_bitmap++; + iterator->_next_bitmap = radiotap_header->it_optional; iterator->_vns = vns; iterator->current_namespace = &radiotap_ns; iterator->is_radiotap_ns = 1; -- Kees Cook