From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pj1-f52.google.com (mail-pj1-f52.google.com [209.85.216.52]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4C6433481 for ; Wed, 28 Jul 2021 23:33:21 +0000 (UTC) Received: by mail-pj1-f52.google.com with SMTP id g23-20020a17090a5797b02901765d605e14so6436500pji.5 for ; Wed, 28 Jul 2021 16:33:21 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=hFIkjt/HAKYP2gDSt85Hu9GQQgBuaRL3GoR8pjbA0bw=; b=eZq87nPKlWl1J2DEEMJZ0uaEj2HBpzx1uFCKn+eDG74O39BY2fqgYPseftQWhiHZ3p 3PJNkhirHMnzPm0VwpSUdr5bc9yR+trhFp/MOdtZnE7T7uRicxtGEKbYH49hrFM5DKkn 1n46Y3AQgPVx/z+eMIRIv1CuZbfnRiL9Xc4bA= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=hFIkjt/HAKYP2gDSt85Hu9GQQgBuaRL3GoR8pjbA0bw=; b=EYCRgiy4sekjHIkyCwgw5jghunykeQLGsrYspjEROy63nQFk+szd07RMBKTCU73ycT CsiMSTpPBMS7imtO4FgslTs6OlKnP+qxL0Onz6XI0N00XEH3KngbBm8BUTTz45nv3G70 rOzFdFCool7SRp3KEeckMcRt9J/TQCE0Ln7FWXJlTkR9YzNILwemNBA6fx/DuDrEYnuF IFTW0AkK+4s3JoRVzWQbzYlatHAhiXOC0zZ1hbEC1z4TuHVwNl4AutCvs/fgm88jsESZ E97trbMeSK89Sq8oRc0XiA3Zfe93pLSk3s9K2fISUzc9HchuoFh2E9leWWao7dLjm7F8 yTwg== X-Gm-Message-State: AOAM532PUZh5QSqUGuV5xlo9fbV0REk8nzDAFZyyGEzsMye7GbH/fIWn 1RasVpyUPi1BLUI8fCbpfUtBsA== X-Google-Smtp-Source: ABdhPJyDOQNxc6ttxQhAqGxoxWvmp3MMGc7Zv3gC3yqd9RQT0SfNwJrM7aAomvW+xqq4hMTgYf4FHA== X-Received: by 2002:a17:90a:fc95:: with SMTP id ci21mr12127797pjb.176.1627515200829; Wed, 28 Jul 2021 16:33:20 -0700 (PDT) Received: from www.outflux.net (smtp.outflux.net. [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> Precedence: bulk X-Mailing-List: linux-staging@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210728073556.GP1931@kadam> 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