From 2690d97ade05c5325cbf7c72b94b90d265659886 Mon Sep 17 00:00:00 2001 From: Daniel Borkmann Date: Tue, 31 Dec 2013 16:28:39 +0100 Subject: netfilter: nf_nat: fix access to uninitialized buffer in IRC NAT helper Commit 5901b6be885e attempted to introduce IPv6 support into IRC NAT helper. By doing so, the following code seemed to be removed by accident: ip = ntohl(exp->master->tuplehash[IP_CT_DIR_REPLY].tuple.dst.u3.ip); sprintf(buffer, "%u %u", ip, port); pr_debug("nf_nat_irc: inserting '%s' == %pI4, port %u\n", buffer, &ip, port); This leads to the fact that buffer[] was left uninitialized and contained some stack value. When we call nf_nat_mangle_tcp_packet(), we call strlen(buffer) on excatly this uninitialized buffer. If we are unlucky and the skb has enough tailroom, we overwrite resp. leak contents with values that sit on our stack into the packet and send that out to the receiver. Since the rather informal DCC spec [1] does not seem to specify IPv6 support right now, we log such occurences so that admins can act accordingly, and drop the packet. I've looked into XChat source, and IPv6 is not supported there: addresses are in u32 and print via %u format string. Therefore, restore old behaviour as in IPv4, use snprintf(). The IRC helper does not support IPv6 by now. By this, we can safely use strlen(buffer) in nf_nat_mangle_tcp_packet() and prevent a buffer overflow. Also simplify some code as we now have ct variable anyway. [1] http://www.irchelp.org/irchelp/rfc/ctcpspec.html Fixes: 5901b6be885e ("netfilter: nf_nat: support IPv6 in IRC NAT helper") Signed-off-by: Daniel Borkmann Cc: Harald Welte Signed-off-by: Pablo Neira Ayuso --- net/netfilter/nf_nat_irc.c | 32 +++++++++++++++++++++++++++----- 1 file changed, 27 insertions(+), 5 deletions(-) diff --git a/net/netfilter/nf_nat_irc.c b/net/netfilter/nf_nat_irc.c index f02b3605823..1fb2258c353 100644 --- a/net/netfilter/nf_nat_irc.c +++ b/net/netfilter/nf_nat_irc.c @@ -34,10 +34,14 @@ static unsigned int help(struct sk_buff *skb, struct nf_conntrack_expect *exp) { char buffer[sizeof("4294967296 65635")]; + struct nf_conn *ct = exp->master; + union nf_inet_addr newaddr; u_int16_t port; unsigned int ret; /* Reply comes from server. */ + newaddr = ct->tuplehash[IP_CT_DIR_REPLY].tuple.dst.u3; + exp->saved_proto.tcp.port = exp->tuple.dst.u.tcp.port; exp->dir = IP_CT_DIR_REPLY; exp->expectfn = nf_nat_follow_master; @@ -57,17 +61,35 @@ static unsigned int help(struct sk_buff *skb, } if (port == 0) { - nf_ct_helper_log(skb, exp->master, "all ports in use"); + nf_ct_helper_log(skb, ct, "all ports in use"); return NF_DROP; } - ret = nf_nat_mangle_tcp_packet(skb, exp->master, ctinfo, - protoff, matchoff, matchlen, buffer, - strlen(buffer)); + /* strlen("\1DCC CHAT chat AAAAAAAA P\1\n")=27 + * strlen("\1DCC SCHAT chat AAAAAAAA P\1\n")=28 + * strlen("\1DCC SEND F AAAAAAAA P S\1\n")=26 + * strlen("\1DCC MOVE F AAAAAAAA P S\1\n")=26 + * strlen("\1DCC TSEND F AAAAAAAA P S\1\n")=27 + * + * AAAAAAAAA: bound addr (1.0.0.0==16777216, min 8 digits, + * 255.255.255.255==4294967296, 10 digits) + * P: bound port (min 1 d, max 5d (65635)) + * F: filename (min 1 d ) + * S: size (min 1 d ) + * 0x01, \n: terminators + */ + /* AAA = "us", ie. where server normally talks to. */ + snprintf(buffer, sizeof(buffer), "%u %u", ntohl(newaddr.ip), port); + pr_debug("nf_nat_irc: inserting '%s' == %pI4, port %u\n", + buffer, &newaddr.ip, port); + + ret = nf_nat_mangle_tcp_packet(skb, ct, ctinfo, protoff, matchoff, + matchlen, buffer, strlen(buffer)); if (ret != NF_ACCEPT) { - nf_ct_helper_log(skb, exp->master, "cannot mangle packet"); + nf_ct_helper_log(skb, ct, "cannot mangle packet"); nf_ct_unexpect_related(exp); } + return ret; } -- cgit v1.2.3-70-g09d2 From f2661adc0c134d890d84c32d7cb54a2b4d1f0a5f Mon Sep 17 00:00:00 2001 From: Jesper Dangaard Brouer Date: Sat, 4 Jan 2014 14:10:43 +0100 Subject: netfilter: only warn once on wrong seqadj usage Avoid potentially spamming the kernel log with WARN splash messages when catching wrong usage of seqadj, by simply using WARN_ONCE. This is a followup to commit db12cf274353 (netfilter: WARN about wrong usage of sequence number adjustments) Suggested-by: Flavio Leitner Suggested-by: Daniel Borkmann Suggested-by: Florian Westphal Signed-off-by: Jesper Dangaard Brouer Signed-off-by: Pablo Neira Ayuso --- net/netfilter/nf_conntrack_seqadj.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/netfilter/nf_conntrack_seqadj.c b/net/netfilter/nf_conntrack_seqadj.c index b2d38da6782..f6e2ae91a80 100644 --- a/net/netfilter/nf_conntrack_seqadj.c +++ b/net/netfilter/nf_conntrack_seqadj.c @@ -37,7 +37,7 @@ int nf_ct_seqadj_set(struct nf_conn *ct, enum ip_conntrack_info ctinfo, return 0; if (unlikely(!seqadj)) { - WARN(1, "Wrong seqadj usage, missing nfct_seqadj_ext_add()\n"); + WARN_ONCE(1, "Missing nfct_seqadj_ext_add() setup call\n"); return 0; } -- cgit v1.2.3-70-g09d2