[net-next] net: skb_find_text: Ignore patterns extending past 'to'

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 0401f40973a58..975c9a6ffb4ad 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -4267,6 +4267,7 @@  static void skb_ts_finish(struct ts_config *conf, struct ts_state *state)
 unsigned int skb_find_text(struct sk_buff *skb, unsigned int from,
 			   unsigned int to, struct ts_config *config)
 {
+	unsigned int patlen = config->ops->get_pattern_len(config);
 	struct ts_state state;
 	unsigned int ret;
 
@@ -4278,7 +4279,7 @@  unsigned int skb_find_text(struct sk_buff *skb, unsigned int from,
 	skb_prepare_seq_read(skb, from, to, TS_SKB_CB(&state));
 
 	ret = textsearch_find(config, &state);
-	return (ret <= to - from ? ret : UINT_MAX);
+	return (ret + patlen <= to - from ? ret : UINT_MAX);
 }
 EXPORT_SYMBOL(skb_find_text);
 
diff --git a/tools/testing/selftests/netfilter/xt_string.sh b/tools/testing/selftests/netfilter/xt_string.sh
new file mode 100755
index 0000000000000..1802653a47287
--- /dev/null
+++ b/tools/testing/selftests/netfilter/xt_string.sh
@@ -0,0 +1,128 @@ 
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+
+# return code to signal skipped test
+ksft_skip=4
+rc=0
+
+if ! iptables --version >/dev/null 2>&1; then
+	echo "SKIP: Test needs iptables"
+	exit $ksft_skip
+fi
+if ! ip -V >/dev/null 2>&1; then
+	echo "SKIP: Test needs iproute2"
+	exit $ksft_skip
+fi
+if ! nc -h >/dev/null 2>&1; then
+	echo "SKIP: Test needs netcat"
+	exit $ksft_skip
+fi
+
+pattern="foo bar baz"
+patlen=11
+hdrlen=$((20 + 8)) # IPv4 + UDP
+ns="ns-$(mktemp -u XXXXXXXX)"
+trap 'ip netns del $ns' EXIT
+ip netns add "$ns"
+ip -net "$ns" link add d0 type dummy
+ip -net "$ns" link set d0 up
+ip -net "$ns" addr add 10.1.2.1/24 dev d0
+
+#ip netns exec "$ns" tcpdump -npXi d0 &
+#tcpdump_pid=$!
+#trap 'kill $tcpdump_pid; ip netns del $ns' EXIT
+
+add_rule() { # (alg, from, to)
+	ip netns exec "$ns" \
+		iptables -A OUTPUT -o d0 -m string \
+			--string "$pattern" --algo $1 --from $2 --to $3
+}
+showrules() { # ()
+	ip netns exec "$ns" iptables -v -S OUTPUT | grep '^-A'
+}
+zerorules() {
+	ip netns exec "$ns" iptables -Z OUTPUT
+}
+countrule() { # (pattern)
+	showrules | grep -c -- "$*"
+}
+send() { # (offset)
+	( for ((i = 0; i < $1 - $hdrlen; i++)); do
+		printf " "
+	  done
+	  printf "$pattern"
+	) | ip netns exec "$ns" nc -w 1 -u 10.1.2.2 27374
+}
+
+add_rule bm 1000 1500
+add_rule bm 1400 1600
+add_rule kmp 1000 1500
+add_rule kmp 1400 1600
+
+zerorules
+send 0
+send $((1000 - $patlen))
+if [ $(countrule -c 0 0) -ne 4 ]; then
+	echo "FAIL: rules match data before --from"
+	showrules
+	((rc--))
+fi
+
+zerorules
+send 1000
+send $((1400 - $patlen))
+if [ $(countrule -c 2) -ne 2 ]; then
+	echo "FAIL: only two rules should match at low offset"
+	showrules
+	((rc--))
+fi
+
+zerorules
+send $((1500 - $patlen))
+if [ $(countrule -c 1) -ne 4 ]; then
+	echo "FAIL: all rules should match at end of packet"
+	showrules
+	((rc--))
+fi
+
+zerorules
+send 1495
+if [ $(countrule -c 1) -ne 1 ]; then
+	echo "FAIL: only kmp with proper --to should match pattern spanning fragments"
+	showrules
+	((rc--))
+fi
+
+zerorules
+send 1500
+if [ $(countrule -c 1) -ne 2 ]; then
+	echo "FAIL: two rules should match pattern at start of second fragment"
+	showrules
+	((rc--))
+fi
+
+zerorules
+send $((1600 - $patlen))
+if [ $(countrule -c 1) -ne 2 ]; then
+	echo "FAIL: two rules should match pattern at end of largest --to"
+	showrules
+	((rc--))
+fi
+
+zerorules
+send $((1600 - $patlen + 1))
+if [ $(countrule -c 1) -ne 0 ]; then
+	echo "FAIL: no rules should match pattern extending largest --to"
+	showrules
+	((rc--))
+fi
+
+zerorules
+send 1600
+if [ $(countrule -c 1) -ne 0 ]; then
+	echo "FAIL: no rule should match pattern past largest --to"
+	showrules
+	((rc--))
+fi
+
+exit $rc