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([2405:201:6008:6ce2:9fb0:9db:90a4:39e2]) by smtp.googlemail.com with ESMTPSA id t5sm3843080pfd.133.2021.08.19.07.34.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 19 Aug 2021 07:34:54 -0700 (PDT) From: Shreyansh Chouhan To: davem@davemloft.net, yoshfuji@linux-ipv6.org, dsahern@kernel.org, kuba@kernel.org, willemdebruijn.kernel@gmail.com Cc: Shreyansh Chouhan , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, syzbot+ff8e1b9f2f36481e2efc@syzkaller.appspotmail.com Subject: [PATCH] ip_gre/ip6_gre: add check for invalid csum_start Date: Thu, 19 Aug 2021 20:04:47 +0530 Message-Id: <20210819143447.314539-1-chouhan.shreyansh630@gmail.com> X-Mailer: git-send-email 2.31.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org If we get a ip gre packet with TUNNEL_CSUM set, an invalid csum_start value causes skb->csum_start offset to be less than the offset for skb->data after we pull the ip header from the packet during the ipgre_xmit call. This patch adds a sanity check to gre_handle_offloads, which checks the validity of skb->csum_start after we have pulled the ip header from the packet in the ipgre_xmit call. Reported-by: syzbot+ff8e1b9f2f36481e2efc@syzkaller.appspotmail.com Signed-off-by: Shreyansh Chouhan --- net/ipv4/ip_gre.c | 2 ++ net/ipv6/ip6_gre.c | 2 ++ 2 files changed, 4 insertions(+) diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c index 12dca0c85f3c..95419b7adf5c 100644 --- a/net/ipv4/ip_gre.c +++ b/net/ipv4/ip_gre.c @@ -473,6 +473,8 @@ static void __gre_xmit(struct sk_buff *skb, struct net_device *dev, static int gre_handle_offloads(struct sk_buff *skb, bool csum) { + if (csum && skb_checksum_start(skb) < skb->data) + return -EINVAL; return iptunnel_handle_offloads(skb, csum ? SKB_GSO_GRE_CSUM : SKB_GSO_GRE); } diff --git a/net/ipv6/ip6_gre.c b/net/ipv6/ip6_gre.c index bc224f917bbd..7a5e90e09363 100644 --- a/net/ipv6/ip6_gre.c +++ b/net/ipv6/ip6_gre.c @@ -629,6 +629,8 @@ static int gre_rcv(struct sk_buff *skb) static int gre_handle_offloads(struct sk_buff *skb, bool csum) { + if (csum && skb_checksum_start(skb) < skb->data) + return -EINVAL; return iptunnel_handle_offloads(skb, csum ? SKB_GSO_GRE_CSUM : SKB_GSO_GRE); } -- 2.31.1