Commit 6a2b7244 authored Mar 25, 2026 by Weiming Shi Committed by Pablo Neira Ayuso Mar 26, 2026

netfilter: nf_conntrack_sip: fix use of uninitialized rtp_addr in process_sdp



process_sdp() declares union nf_inet_addr rtp_addr on the stack and
passes it to the nf_nat_sip sdp_session hook after walking the SDP
media descriptions. However rtp_addr is only initialized inside the
media loop when a recognized media type with a non-zero port is found.

If the SDP body contains no m= lines, only inactive media sections
(m=audio 0 ...) or only unrecognized media types, rtp_addr is never
assigned. Despite that, the function still calls hooks->sdp_session()
with &rtp_addr, causing nf_nat_sdp_session() to format the stale stack
value as an IP address and rewrite the SDP session owner and connection
lines with it.

With CONFIG_INIT_STACK_ALL_ZERO (default on most distributions) this
results in the session-level o= and c= addresses being rewritten to
0.0.0.0 for inactive SDP sessions. Without stack auto-init the
rewritten address is whatever happened to be on the stack.

Fix this by pre-initializing rtp_addr from the session-level connection
address (caddr) when available, and tracking via a have_rtp_addr flag
whether any valid address was established. Skip the sdp_session hook
entirely when no valid address exists.

Fixes: 4ab9e64e ("[NETFILTER]: nf_nat_sip: split up SDP mangling")
Reported-by: Xiang Mei <xmei5@asu.edu>
Signed-off-by: Weiming Shi <bestswngs@gmail.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

parent 3db56479

net/netfilter/nf_conntrack_sip.c

+10 −4

Original line number	Diff line number	Diff line
		@@ -1040,6 +1040,7 @@ static int process_sdp(struct sk_buff *skb, unsigned int protoff,
		unsigned int port;
		const struct sdp_media_type *t;
		int ret = NF_ACCEPT;
		bool have_rtp_addr = false;

		hooks = rcu_dereference(nf_nat_sip_hooks);

		@@ -1056,8 +1057,11 @@ static int process_sdp(struct sk_buff *skb, unsigned int protoff,
		caddr_len = 0;
		if (ct_sip_parse_sdp_addr(ct, dptr, sdpoff, datalen,
		SDP_HDR_CONNECTION, SDP_HDR_MEDIA,
		&matchoff, &matchlen, &caddr) > 0)
		&matchoff, &matchlen, &caddr) > 0) {
		caddr_len = matchlen;
		memcpy(&rtp_addr, &caddr, sizeof(rtp_addr));
		have_rtp_addr = true;
		}

		mediaoff = sdpoff;
		for (i = 0; i < ARRAY_SIZE(sdp_media_types); ) {
		@@ -1091,9 +1095,11 @@ static int process_sdp(struct sk_buff *skb, unsigned int protoff,
		&matchoff, &matchlen, &maddr) > 0) {
		maddr_len = matchlen;
		memcpy(&rtp_addr, &maddr, sizeof(rtp_addr));
		} else if (caddr_len)
		have_rtp_addr = true;
		} else if (caddr_len) {
		memcpy(&rtp_addr, &caddr, sizeof(rtp_addr));
		else {
		have_rtp_addr = true;
		} else {
		nf_ct_helper_log(skb, ct, "cannot parse SDP message");
		return NF_DROP;
		}
		@@ -1125,7 +1131,7 @@ static int process_sdp(struct sk_buff *skb, unsigned int protoff,

		/* Update session connection and owner addresses */
		hooks = rcu_dereference(nf_nat_sip_hooks);
		if (hooks && ct->status & IPS_NAT_MASK)
		if (hooks && ct->status & IPS_NAT_MASK && have_rtp_addr)
		ret = hooks->sdp_session(skb, protoff, dataoff,
		dptr, datalen, sdpoff,
		&rtp_addr);