From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Eric Dumazet" , "Pablo Neira Ayuso" , "Denys Fedoryshchenko" Date: Sun, 11 Feb 2018 04:20:06 +0000 Message-ID: Subject: [PATCH 3.2 66/79] netfilter: xt_TCPMSS: add more sanity tests on tcph->doff In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-ID: 3.2.99-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Eric Dumazet commit 2638fd0f92d4397884fd991d8f4925cb3f081901 upstream. Denys provided an awesome KASAN report pointing to an use after free in xt_TCPMSS I have provided three patches to fix this issue, either in xt_TCPMSS or in xt_tcpudp.c. It seems xt_TCPMSS patch has the smallest possible impact. Signed-off-by: Eric Dumazet Reported-by: Denys Fedoryshchenko Signed-off-by: Pablo Neira Ayuso Signed-off-by: Ben Hutchings --- net/netfilter/xt_TCPMSS.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) --- a/net/netfilter/xt_TCPMSS.c +++ b/net/netfilter/xt_TCPMSS.c @@ -71,7 +71,7 @@ tcpmss_mangle_packet(struct sk_buff *skb tcph = (struct tcphdr *)(skb_network_header(skb) + tcphoff); tcp_hdrlen = tcph->doff * 4; - if (len < tcp_hdrlen) + if (len < tcp_hdrlen || tcp_hdrlen < sizeof(struct tcphdr)) return -1; if (info->mss == XT_TCPMSS_CLAMP_PMTU) { @@ -122,6 +122,10 @@ tcpmss_mangle_packet(struct sk_buff *skb if (len > tcp_hdrlen) return 0; + /* tcph->doff has 4 bits, do not wrap it to 0 */ + if (tcp_hdrlen >= 15 * 4) + return 0; + /* * MSS Option not found ?! add it.. */