[PATCH net 07/14] netfilter: conntrack: remove sprintf usage

Pablo Neira Ayuso
2026-04-16T01:31:18Z

From: Florian Westphal <fw@strlen.de>

Replace it with scnprintf, the buffer sizes are expected to be large enough
to hold the result, no need for snprintf+overflow check.

Increase buffer size in mangle_content_len() while at it.

BUG: KASAN: stack-out-of-bounds in vsnprintf+0xea5/0x1270
Write of size 1 at addr [..]
vsnprintf+0xea5/0x1270
sprintf+0xb1/0xe0
mangle_content_len+0x1ac/0x280
nf_nat_sdp_session+0x1cc/0x240
process_sdp+0x8f8/0xb80
process_invite_request+0x108/0x2b0
process_sip_msg+0x5da/0xf50
sip_help_tcp+0x45e/0x780
nf_confirm+0x34d/0x990
[..]

Fixes: 9fafcd7b2032 ("[NETFILTER]: nf_conntrack/nf_nat: add SIP helper port")
Reported-by: Yiming Qian <yimingqian591@gmail.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
---
net/netfilter/nf_nat_amanda.c | 2 +-
net/netfilter/nf_nat_sip.c | 33 ++++++++++++++++++---------------
2 files changed, 19 insertions(+), 16 deletions(-)

diff --git a/net/netfilter/nf_nat_amanda.c b/net/netfilter/nf_nat_amanda.c
index 98deef6cde69..8f1054920a85 100644
--- a/net/netfilter/nf_nat_amanda.c
+++ b/net/netfilter/nf_nat_amanda.c
@@ -50,7 +50,7 @@ static unsigned int help(struct sk_buff *skb,
return NF_DROP;
}

- sprintf(buffer, "%u", port);
+ snprintf(buffer, sizeof(buffer), "%u", port);
if (!nf_nat_mangle_udp_packet(skb, exp->master, ctinfo,
protoff, matchoff, matchlen,
buffer, strlen(buffer))) {
diff --git a/net/netfilter/nf_nat_sip.c b/net/netfilter/nf_nat_sip.c
index cf4aeb299bde..c845b6d1a2bd 100644
--- a/net/netfilter/nf_nat_sip.c
+++ b/net/netfilter/nf_nat_sip.c
@@ -68,25 +68,27 @@ static unsigned int mangle_packet(struct sk_buff *skb, unsigned int protoff,
}

static int sip_sprintf_addr(const struct nf_conn *ct, char *buffer,
+ size_t size,
const union nf_inet_addr *addr, bool delim)
{
if (nf_ct_l3num(ct) == NFPROTO_IPV4)
- return sprintf(buffer, "%pI4", &addr->ip);
+ return scnprintf(buffer, size, "%pI4", &addr->ip);
else {
if (delim)
- return sprintf(buffer, "[%pI6c]", &addr->ip6);
+ return scnprintf(buffer, size, "[%pI6c]", &addr->ip6);
else
- return sprintf(buffer, "%pI6c", &addr->ip6);
+ return scnprintf(buffer, size, "%pI6c", &addr->ip6);
}
}

static int sip_sprintf_addr_port(const struct nf_conn *ct, char *buffer,
+ size_t size,
const union nf_inet_addr *addr, u16 port)
{
if (nf_ct_l3num(ct) == NFPROTO_IPV4)
- return sprintf(buffer, "%pI4:%u", &addr->ip, port);
+ return scnprintf(buffer, size, "%pI4:%u", &addr->ip, port);
else
- return sprintf(buffer, "[%pI6c]:%u", &addr->ip6, port);
+ return scnprintf(buffer, size, "[%pI6c]:%u", &addr->ip6, port);
}

static int map_addr(struct sk_buff *skb, unsigned int protoff,
@@ -119,7 +121,7 @@ static int map_addr(struct sk_buff *skb, unsigned int protoff,
if (nf_inet_addr_cmp(&newaddr, addr) && newport == port)
return 1;

- buflen = sip_sprintf_addr_port(ct, buffer, &newaddr, ntohs(newport));
+ buflen = sip_sprintf_addr_port(ct, buffer, sizeof(buffer), &newaddr, ntohs(newport));
return mangle_packet(skb, protoff, dataoff, dptr, datalen,
matchoff, matchlen, buffer, buflen);
}
@@ -212,7 +214,7 @@ static unsigned int nf_nat_sip(struct sk_buff *skb, unsigned int protoff,
&addr, true) > 0 &&
nf_inet_addr_cmp(&addr, &ct->tuplehash[dir].tuple.src.u3) &&
!nf_inet_addr_cmp(&addr, &ct->tuplehash[!dir].tuple.dst.u3)) {
- buflen = sip_sprintf_addr(ct, buffer,
+ buflen = sip_sprintf_addr(ct, buffer, sizeof(buffer),
&ct->tuplehash[!dir].tuple.dst.u3,
true);
if (!mangle_packet(skb, protoff, dataoff, dptr, datalen,
@@ -229,7 +231,7 @@ static unsigned int nf_nat_sip(struct sk_buff *skb, unsigned int protoff,
&addr, false) > 0 &&
nf_inet_addr_cmp(&addr, &ct->tuplehash[dir].tuple.dst.u3) &&
!nf_inet_addr_cmp(&addr, &ct->tuplehash[!dir].tuple.src.u3)) {
- buflen = sip_sprintf_addr(ct, buffer,
+ buflen = sip_sprintf_addr(ct, buffer, sizeof(buffer),
&ct->tuplehash[!dir].tuple.src.u3,
false);
if (!mangle_packet(skb, protoff, dataoff, dptr, datalen,
@@ -247,7 +249,7 @@ static unsigned int nf_nat_sip(struct sk_buff *skb, unsigned int protoff,
htons(n) == ct->tuplehash[dir].tuple.dst.u.udp.port &&
htons(n) != ct->tuplehash[!dir].tuple.src.u.udp.port) {
__be16 p = ct->tuplehash[!dir].tuple.src.u.udp.port;
- buflen = sprintf(buffer, "%u", ntohs(p));
+ buflen = scnprintf(buffer, sizeof(buffer), "%u", ntohs(p));
if (!mangle_packet(skb, protoff, dataoff, dptr, datalen,
poff, plen, buffer, buflen)) {
nf_ct_helper_log(skb, ct, "cannot mangle rport");
@@ -418,7 +420,8 @@ static unsigned int nf_nat_sip_expect(struct sk_buff *skb, unsigned int protoff,

if (!nf_inet_addr_cmp(&exp->tuple.dst.u3, &exp->saved_addr) ||
exp->tuple.dst.u.udp.port != exp->saved_proto.udp.port) {
- buflen = sip_sprintf_addr_port(ct, buffer, &newaddr, port);
+ buflen = sip_sprintf_addr_port(ct, buffer, sizeof(buffer),
+ &newaddr, port);
if (!mangle_packet(skb, protoff, dataoff, dptr, datalen,
matchoff, matchlen, buffer, buflen)) {
nf_ct_helper_log(skb, ct, "cannot mangle packet");
@@ -438,8 +441,8 @@ static int mangle_content_len(struct sk_buff *skb, unsigned int protoff,
{
enum ip_conntrack_info ctinfo;
struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
+ char buffer[sizeof("4294967295")];
unsigned int matchoff, matchlen;
- char buffer[sizeof("65536")];
int buflen, c_len;

/* Get actual SDP length */
@@ -454,7 +457,7 @@ static int mangle_content_len(struct sk_buff *skb, unsigned int protoff,
&matchoff, &matchlen) <= 0)
return 0;

- buflen = sprintf(buffer, "%u", c_len);
+ buflen = scnprintf(buffer, sizeof(buffer), "%u", c_len);
return mangle_packet(skb, protoff, dataoff, dptr, datalen,
matchoff, matchlen, buffer, buflen);
}
@@ -491,7 +494,7 @@ static unsigned int nf_nat_sdp_addr(struct sk_buff *skb, unsigned int protoff,
char buffer[INET6_ADDRSTRLEN];
unsigned int buflen;

- buflen = sip_sprintf_addr(ct, buffer, addr, false);
+ buflen = sip_sprintf_addr(ct, buffer, sizeof(buffer), addr, false);
if (mangle_sdp_packet(skb, protoff, dataoff, dptr, datalen,
sdpoff, type, term, buffer, buflen))
return 0;
@@ -509,7 +512,7 @@ static unsigned int nf_nat_sdp_port(struct sk_buff *skb, unsigned int protoff,
char buffer[sizeof("nnnnn")];
unsigned int buflen;

- buflen = sprintf(buffer, "%u", port);
+ buflen = scnprintf(buffer, sizeof(buffer), "%u", port);
if (!mangle_packet(skb, protoff, dataoff, dptr, datalen,
matchoff, matchlen, buffer, buflen))
return 0;
@@ -529,7 +532,7 @@ static unsigned int nf_nat_sdp_session(struct sk_buff *skb, unsigned int protoff
unsigned int buflen;

/* Mangle session description owner and contact addresses */
- buflen = sip_sprintf_addr(ct, buffer, addr, false);
+ buflen = sip_sprintf_addr(ct, buffer, sizeof(buffer), addr, false);
if (mangle_sdp_packet(skb, protoff, dataoff, dptr, datalen, sdpoff,
SDP_HDR_OWNER, SDP_HDR_MEDIA, buffer, buflen))
return 0;
--
2.47.3