[PATCH nf] netfilter: nf_conntrack_sip: widen NAT rewrite delta to s32 in sip_help_tcp()

[Xiang Mei]

sip_help_tcp() stores the size change of each NAT-rewritten SIP message
in s16 diff and accumulates it in s16 tdiff, but a single message can
grow by more than S16_MAX while the packet stays under the 65535
enlarge_skb() limit: nf_nat_sip() rewrites every matching URI, and a long
Contact list expands the message by tens of kilobytes. diff then wraps,
and "datalen = datalen + diff - msglen" yields a huge unsigned datalen,
so the next iteration's ct_sip_get_header() reads past the linearized skb
tail.

Widen diff, tdiff and the seq_adjust hook to s32. Both are bounded by the
65535 byte packet limit, and the seqadj core is already s32
(nf_ct_seqadj_set() takes s32), so no previously accepted input is
rejected.

  BUG: KASAN: use-after-free in ct_sip_get_header (net/netfilter/nf_conntrack_sip.c:464)
  Read of size 1 at addr ffff888010800000 by task ksoftirqd/1/25
   ct_sip_get_header (net/netfilter/nf_conntrack_sip.c:464)
   sip_help_tcp (net/netfilter/nf_conntrack_sip.c:1694)
   nf_confirm (net/netfilter/nf_conntrack_proto.c:183)
   nf_hook_slow (net/netfilter/core.c:619)
   ip6_output (net/ipv6/ip6_output.c:246)
   ip6_forward (net/ipv6/ip6_output.c:690)
   ipv6_rcv (net/ipv6/ip6_input.c:351)
   __netif_receive_skb_one_core (net/core/dev.c:6212)
   process_backlog (net/core/dev.c:6676)
   __napi_poll (net/core/dev.c:7735)
   net_rx_action (net/core/dev.c:7955)
   handle_softirqs (kernel/softirq.c:622)
   run_ksoftirqd (kernel/softirq.c:1076)
   ...

Fixes: f5b321bd37fb ("netfilter: nf_conntrack_sip: add TCP support")
Reported-by: Weiming Shi <bestswngs@xxxxxxxxx>
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Xiang Mei <xmei5@xxxxxxx>
---
 include/linux/netfilter/nf_conntrack_sip.h | 2 +-
 net/netfilter/nf_conntrack_sip.c           | 2 +-
 net/netfilter/nf_nat_sip.c                 | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/linux/netfilter/nf_conntrack_sip.h b/include/linux/netfilter/nf_conntrack_sip.h
index dbc614dfe0d5..aafa0c04f917 100644
--- a/include/linux/netfilter/nf_conntrack_sip.h
+++ b/include/linux/netfilter/nf_conntrack_sip.h
@@ -115,7 +115,7 @@ struct nf_nat_sip_hooks {
 			    unsigned int *datalen);
 
 	void (*seq_adjust)(struct sk_buff *skb,
-			   unsigned int protoff, s16 off);
+			   unsigned int protoff, s32 off);
 
 	unsigned int (*expect)(struct sk_buff *skb,
 			       unsigned int protoff,
diff --git a/net/netfilter/nf_conntrack_sip.c b/net/netfilter/nf_conntrack_sip.c
index f3f90a866338..e4a70d1d77b0 100644
--- a/net/netfilter/nf_conntrack_sip.c
+++ b/net/netfilter/nf_conntrack_sip.c
@@ -1663,7 +1663,7 @@ static int sip_help_tcp(struct sk_buff *skb, unsigned int protoff,
 	unsigned int matchoff, matchlen;
 	unsigned int msglen, origlen;
 	const char *dptr, *end;
-	s16 diff, tdiff = 0;
+	s32 diff, tdiff = 0;
 	int ret = NF_ACCEPT;
 	unsigned long clen;
 	bool term;
diff --git a/net/netfilter/nf_nat_sip.c b/net/netfilter/nf_nat_sip.c
index aea02f6aff09..a93eaf0f7d30 100644
--- a/net/netfilter/nf_nat_sip.c
+++ b/net/netfilter/nf_nat_sip.c
@@ -321,7 +321,7 @@ static unsigned int nf_nat_sip(struct sk_buff *skb, unsigned int protoff,
 }
 
 static void nf_nat_sip_seq_adjust(struct sk_buff *skb, unsigned int protoff,
-				  s16 off)
+				  s32 off)
 {
 	enum ip_conntrack_info ctinfo;
 	struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
-- 
2.43.0