3.2.99-rc1 review patch. If anyone has any objections, please let me know.
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From: Pablo Neira Ayuso pablo@netfilter.org
commit bc6bcb59dd7c184d229f9e86d08aa56059938a4c upstream.
This target assumes that tcph->doff is well-formed, that may be well not the case. Add extra sanity checkings to avoid possible crash due to read/write out of the real packet boundary. After this patch, the default action on malformed TCP packets is to drop them. Moreover, fragments are skipped.
Reported-by: Rafal Kupka rkupka@telemetry.com Signed-off-by: Pablo Neira Ayuso pablo@netfilter.org Signed-off-by: Ben Hutchings ben@decadent.org.uk --- net/netfilter/xt_TCPOPTSTRIP.c | 17 ++++++++++++++--- 1 file changed, 14 insertions(+), 3 deletions(-)
--- a/net/netfilter/xt_TCPOPTSTRIP.c +++ b/net/netfilter/xt_TCPOPTSTRIP.c @@ -30,17 +30,28 @@ static inline unsigned int optlen(const
static unsigned int tcpoptstrip_mangle_packet(struct sk_buff *skb, - const struct xt_tcpoptstrip_target_info *info, + const struct xt_action_param *par, unsigned int tcphoff, unsigned int minlen) { + const struct xt_tcpoptstrip_target_info *info = par->targinfo; unsigned int optl, i, j; struct tcphdr *tcph; u_int16_t n, o; u_int8_t *opt; + int len; + + /* This is a fragment, no TCP header is available */ + if (par->fragoff != 0) + return XT_CONTINUE;
if (!skb_make_writable(skb, skb->len)) return NF_DROP;
+ len = skb->len - tcphoff; + if (len < (int)sizeof(struct tcphdr) || + tcp_hdr(skb)->doff * 4 > len) + return NF_DROP; + tcph = (struct tcphdr *)(skb_network_header(skb) + tcphoff); opt = (u_int8_t *)tcph;
@@ -76,7 +87,7 @@ tcpoptstrip_mangle_packet(struct sk_buff static unsigned int tcpoptstrip_tg4(struct sk_buff *skb, const struct xt_action_param *par) { - return tcpoptstrip_mangle_packet(skb, par->targinfo, ip_hdrlen(skb), + return tcpoptstrip_mangle_packet(skb, par, ip_hdrlen(skb), sizeof(struct iphdr) + sizeof(struct tcphdr)); }
@@ -93,7 +104,7 @@ tcpoptstrip_tg6(struct sk_buff *skb, con if (tcphoff < 0) return NF_DROP;
- return tcpoptstrip_mangle_packet(skb, par->targinfo, tcphoff, + return tcpoptstrip_mangle_packet(skb, par, tcphoff, sizeof(*ipv6h) + sizeof(struct tcphdr)); } #endif