[PATCH net 02/14] netfilter: nf_conntrack_sip: add bounds-checked port parsing helper

Pablo Neira Ayuso
2026-04-16T01:31:11Z

From: Jenny Guanni Qu <qguanni@gmail.com>

Replace unsafe port parsing in epaddr_len(), ct_sip_parse_header_uri(),
and ct_sip_parse_request() with a new sip_parse_port() helper that
validates each digit against the buffer limit, eliminating the use of
simple_strtoul() which assumes NUL-terminated strings.

The previous code dereferenced pointers without bounds checks after
sip_parse_addr() and relied on simple_strtoul() on non-NUL-terminated
skb data. A port that reaches the buffer limit without a trailing
character is also rejected as malformed.

Based on a suggestion by Florian Westphal.

[ fw@strlen.de: make port range check unconditional ]

Fixes: 05e3ced297fe ("[NETFILTER]: nf_conntrack_sip: introduce SIP-URI parsing helper")
Reported-by: Klaudia Kloc <klaudia@vidocsecurity.com>
Reported-by: Dawid Moczadło <dawid@vidocsecurity.com>
Suggested-by: Florian Westphal <fw@strlen.de>
Tested-by: Jenny Guanni Qu <qguanni@gmail.com>
Tested-by: Weiming Shi <bestswngs@gmail.com>
Signed-off-by: Jenny Guanni Qu <qguanni@gmail.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
---
net/netfilter/nf_conntrack_sip.c | 80 +++++++++++++++++++++++---------
1 file changed, 57 insertions(+), 23 deletions(-)

diff --git a/net/netfilter/nf_conntrack_sip.c b/net/netfilter/nf_conntrack_sip.c
index 939502ff7c87..38a55a3b3d19 100644
--- a/net/netfilter/nf_conntrack_sip.c
+++ b/net/netfilter/nf_conntrack_sip.c
@@ -181,6 +181,57 @@ static int sip_parse_addr(const struct nf_conn *ct, const char *cp,
return 1;
}

+/* Parse optional port number after IP address.
+ * Returns false on malformed input, true otherwise.
+ * If port is non-NULL, stores parsed port in network byte order.
+ * If no port is present, sets *port to default SIP port.
+ */
+static bool sip_parse_port(const char *dptr, const char **endp,
+ const char *limit, __be16 *port)
+{
+ unsigned int p = 0;
+ int len = 0;
+
+ if (dptr >= limit)
+ return false;
+
+ if (*dptr != ':') {
+ if (port)
+ *port = htons(SIP_PORT);
+ if (endp)
+ *endp = dptr;
+ return true;
+ }
+
+ dptr++; /* skip ':' */
+
+ while (dptr < limit && isdigit(*dptr)) {
+ p = p * 10 + (*dptr - '0');
+ dptr++;
+ len++;
+ if (len > 5) /* max "65535" */
+ return false;
+ }
+
+ if (len == 0)
+ return false;
+
+ /* reached limit while parsing port */
+ if (dptr >= limit)
+ return false;
+
+ if (p < 1024 || p > 65535)
+ return false;
+
+ if (port)
+ *port = htons(p);
+
+ if (endp)
+ *endp = dptr;
+
+ return true;
+}
+
/* skip ip address. returns its length. */
static int epaddr_len(const struct nf_conn *ct, const char *dptr,
const char *limit, int *shift)
@@ -193,11 +244,8 @@ static int epaddr_len(const struct nf_conn *ct, const char *dptr,
return 0;
}

- /* Port number */
- if (*dptr == ':') {
- dptr++;
- dptr += digits_len(ct, dptr, limit, shift);
- }
+ if (!sip_parse_port(dptr, &dptr, limit, NULL))
+ return 0;
return dptr - aux;
}

@@ -241,7 +289,6 @@ int ct_sip_parse_request(const struct nf_conn *ct,
{
const char *start = dptr, *limit = dptr + datalen, *end;
unsigned int mlen;
- unsigned int p;
int shift = 0;

/* Skip method and following whitespace */
@@ -267,14 +314,8 @@ int ct_sip_parse_request(const struct nf_conn *ct,

if (!sip_parse_addr(ct, dptr, &end, addr, limit, true))
return -1;
- if (end < limit && *end == ':') {
- end++;
- p = simple_strtoul(end, (char **)&end, 10);
- if (p < 1024 || p > 65535)
- return -1;
- *port = htons(p);
- } else
- *port = htons(SIP_PORT);
+ if (!sip_parse_port(end, &end, limit, port))
+ return -1;

if (end == dptr)
return 0;
@@ -509,7 +550,6 @@ int ct_sip_parse_header_uri(const struct nf_conn *ct, const char *dptr,
union nf_inet_addr *addr, __be16 *port)
{
const char *c, *limit = dptr + datalen;
- unsigned int p;
int ret;

ret = ct_sip_walk_headers(ct, dptr, dataoff ? *dataoff : 0, datalen,
@@ -520,14 +560,8 @@ int ct_sip_parse_header_uri(const struct nf_conn *ct, const char *dptr,

if (!sip_parse_addr(ct, dptr + *matchoff, &c, addr, limit, true))
return -1;
- if (*c == ':') {
- c++;
- p = simple_strtoul(c, (char **)&c, 10);
- if (p < 1024 || p > 65535)
- return -1;
- *port = htons(p);
- } else
- *port = htons(SIP_PORT);
+ if (!sip_parse_port(c, &c, limit, port))
+ return -1;

if (dataoff)
*dataoff = c - dptr;
--
2.47.3