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authorPablo Neira Ayuso <pablo@netfilter.org>2013-07-25 10:37:49 +0200
committerPablo Neira Ayuso <pablo@netfilter.org>2013-08-01 11:42:53 +0200
commit71ffe9c77dd7a2b62207953091efa8dafec958dd (patch)
treed0251ec9b294378915562e50a62ae095616d5430
parenta661b43fd047ef501da43a19975415f861c7c3db (diff)
netfilter: xt_TCPMSS: fix handling of malformed TCP header and options
Make sure the packet has enough room for the TCP header and that it is not malformed. While at it, store tcph->doff*4 in a variable, as it is used several times. This patch also fixes a possible off by one in case of malformed TCP options. Reported-by: Julian Anastasov <ja@ssi.bg> Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
-rw-r--r--net/netfilter/xt_TCPMSS.c28
1 files changed, 16 insertions, 12 deletions
diff --git a/net/netfilter/xt_TCPMSS.c b/net/netfilter/xt_TCPMSS.c
index 7011c71646f0..6113cc7efffc 100644
--- a/net/netfilter/xt_TCPMSS.c
+++ b/net/netfilter/xt_TCPMSS.c
@@ -52,7 +52,8 @@ tcpmss_mangle_packet(struct sk_buff *skb,
{
const struct xt_tcpmss_info *info = par->targinfo;
struct tcphdr *tcph;
- unsigned int tcplen, i;
+ int len, tcp_hdrlen;
+ unsigned int i;
__be16 oldval;
u16 newmss;
u8 *opt;
@@ -64,11 +65,14 @@ tcpmss_mangle_packet(struct sk_buff *skb,
if (!skb_make_writable(skb, skb->len))
return -1;
- tcplen = skb->len - tcphoff;
+ len = skb->len - tcphoff;
+ if (len < (int)sizeof(struct tcphdr))
+ return -1;
+
tcph = (struct tcphdr *)(skb_network_header(skb) + tcphoff);
+ tcp_hdrlen = tcph->doff * 4;
- /* Header cannot be larger than the packet */
- if (tcplen < tcph->doff*4)
+ if (len < tcp_hdrlen)
return -1;
if (info->mss == XT_TCPMSS_CLAMP_PMTU) {
@@ -87,9 +91,8 @@ tcpmss_mangle_packet(struct sk_buff *skb,
newmss = info->mss;
opt = (u_int8_t *)tcph;
- for (i = sizeof(struct tcphdr); i < tcph->doff*4; i += optlen(opt, i)) {
- if (opt[i] == TCPOPT_MSS && tcph->doff*4 - i >= TCPOLEN_MSS &&
- opt[i+1] == TCPOLEN_MSS) {
+ for (i = sizeof(struct tcphdr); i <= tcp_hdrlen - TCPOLEN_MSS; i += optlen(opt, i)) {
+ if (opt[i] == TCPOPT_MSS && opt[i+1] == TCPOLEN_MSS) {
u_int16_t oldmss;
oldmss = (opt[i+2] << 8) | opt[i+3];
@@ -112,9 +115,10 @@ tcpmss_mangle_packet(struct sk_buff *skb,
}
/* There is data after the header so the option can't be added
- without moving it, and doing so may make the SYN packet
- itself too large. Accept the packet unmodified instead. */
- if (tcplen > tcph->doff*4)
+ * without moving it, and doing so may make the SYN packet
+ * itself too large. Accept the packet unmodified instead.
+ */
+ if (len > tcp_hdrlen)
return 0;
/*
@@ -143,10 +147,10 @@ tcpmss_mangle_packet(struct sk_buff *skb,
newmss = min(newmss, (u16)1220);
opt = (u_int8_t *)tcph + sizeof(struct tcphdr);
- memmove(opt + TCPOLEN_MSS, opt, tcplen - sizeof(struct tcphdr));
+ memmove(opt + TCPOLEN_MSS, opt, len - sizeof(struct tcphdr));
inet_proto_csum_replace2(&tcph->check, skb,
- htons(tcplen), htons(tcplen + TCPOLEN_MSS), 1);
+ htons(len), htons(len + TCPOLEN_MSS), 1);
opt[0] = TCPOPT_MSS;
opt[1] = TCPOLEN_MSS;
opt[2] = (newmss & 0xff00) >> 8;