Subject: [PATCH net 03/11] netfilter: nf_conntrack_sip: fix Content-Length u32 truncation in sip_help_tcp()

From: Florian Westphal <[email-masked]>
Date: Fri, 13 Mar 2026 16:06:06 +0100

From: Lukas Johannes Möller <[email-masked]>

sip_help_tcp() parses the SIP Content-Length header with
simple_strtoul(), which returns unsigned long, but stores the result in
unsigned int clen.  On 64-bit systems, values exceeding UINT_MAX are
silently truncated before computing the SIP message boundary.

For example, Content-Length 4294967328 (2^32 + 32) is truncated to 32,
causing the parser to miscalculate where the current message ends.  The
loop then treats trailing data in the TCP segment as a second SIP
message and processes it through the SDP parser.

Fix this by changing clen to unsigned long to match the return type of
simple_strtoul(), and reject Content-Length values that exceed the
remaining TCP payload length.

Fixes: f5b321bd37fb ("netfilter: nf_conntrack_sip: add TCP support")
Signed-off-by: Lukas Johannes Möller <[email-masked]>
Signed-off-by: Florian Westphal <[email-masked]>
---
 net/netfilter/nf_conntrack_sip.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/net/netfilter/nf_conntrack_sip.c b/net/netfilter/nf_conntrack_sip.c
index ca748f8dbff1..4ab5ef71d96d 100644
--- a/net/netfilter/nf_conntrack_sip.c
+++ b/net/netfilter/nf_conntrack_sip.c
@@ -1534,11 +1534,12 @@ static int sip_help_tcp(struct sk_buff *skb, unsigned int protoff,
 {
 	struct tcphdr *th, _tcph;
 	unsigned int dataoff, datalen;
-	unsigned int matchoff, matchlen, clen;
+	unsigned int matchoff, matchlen;
 	unsigned int msglen, origlen;
 	const char *dptr, *end;
 	s16 diff, tdiff = 0;
 	int ret = NF_ACCEPT;
+	unsigned long clen;
 	bool term;
 
 	if (ctinfo != IP_CT_ESTABLISHED &&
@@ -1573,6 +1574,9 @@ static int sip_help_tcp(struct sk_buff *skb, unsigned int protoff,
 		if (dptr + matchoff == end)
 			break;
 
+		if (clen > datalen)
+			break;
+
 		term = false;
 		for (; end + strlen("\r\n\r\n") <= dptr + datalen; end++) {
 			if (end[0] == '\r' && end[1] == '\n' &&
-- 
2.52.0