[PATCH 6.19 134/220] netfilter: nf_conntrack_sip: fix Content-Length u32 truncation in sip_help_tcp()

Greg Kroah-Hartman
2026-03-23T13:56:14Z

From: Lukas Johannes Möller <research@johannes-moeller.dev>

[ Upstream commit fbce58e719a17aa215c724473fd5baaa4a8dc57c ]

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 <research@johannes-moeller.dev>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 ca748f8dbff13..4ab5ef71d96db 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' &&
--
2.51.0