ping: do a better job with what we received from the net, part 2

When we see a difference between the payload we sent and what we
received, we dump both but we were not prepared for the case when
the received payload is less than we sent.  In this case we were trying
to dump more than needed.

Funny enough, 23 years ago I already fixed a similar issue here but
didn't pay attention to this small dumping loop.

Test written by jlduran.

Reviewed by:	jlduran
MFC after:	1 month
Found with:	Claude Code Sonnet 5

Differential Revision: https://reviews.freebsd.org/D59556
Differential Revision: https://reviews.freebsd.org/D59582

sbin/ping/ping.c

@@ -1109,7 +1109,7 @@ pr_pack(char *buf, ssize_t cc, struct sockaddr_in *from, struct timespec *tv)
 	const u_char *icmp_data_raw;
 	ssize_t icmp_data_raw_len;
 	double triptime;
-	int dupflag, i, j, recv_len;
+	int avail, dupflag, i, j, recv_len;
 	int8_t hlen;
 	uint16_t seq;
 	static int old_rrlen;
@@ -1273,9 +1273,11 @@ pr_pack(char *buf, ssize_t cc, struct sockaddr_in *from, struct timespec *tv)
 	(void)printf("\nwrong data byte #%d should be 0x%x but was 0x%x",
 	    i, *dp, *cp);
 					(void)printf("\ncp:");
+					avail = (int)MIN((ssize_t)datalen,
+					    i + cc);
 					cp = (u_char*)(buf + hlen +
 					    offsetof(struct icmp, icmp_data));
-					for (i = 0; i < datalen; ++i, ++cp) {
+					for (i = 0; i < avail; ++i, ++cp) {
 						if ((i % 16) == 8)
 							(void)printf("\n\t");
 						(void)printf(" %2x", *cp);

sbin/ping/tests/test_ping.py

@@ -80,6 +80,10 @@ def build_response_packet(echo, ip, icmp, oip_ihl, special):
         # Build a package with a wrong last byte
         payload_no_last_byte = sc.bytes_hex(load)[:-2]
         load = (sc.hex_bytes(payload_no_last_byte)) + b"\x00"
+    if special == "short-wrong":
+        # Build a short package with a wrong last byte
+        payload_no_last_byte = sc.bytes_hex(load)[:-4]
+        load = (sc.hex_bytes(payload_no_last_byte)) + b"\x00"
     if special == "not-mine":
         # Modify the ICMP Identifier field
         oicmp.id += 1
@@ -202,7 +206,7 @@ def pinger(
     :keyword oip_ihl: Inner packet's Internet Header Length, defaults to None
     :type oip_ihl: class:`scapy.fields.BitField`, optional
     :keyword special: Send a special packet - one of `no-payload`, `not-mine`,
-        `tcp`, `udp`, `wrong` or `warp`, defaults to None
+        `short-wrong`, `tcp`, `udp`, `wrong` or `warp`, defaults to None
     :type special: str, optional
     :keyword icmp_pptr: ICMP pointer, defaults to 0
     :type icmp_pptr: class:`scapy.fields.ByteField`
@@ -1464,6 +1468,40 @@ round-trip min/avg/max/stddev = /// ms
             },
             id="_0_0_special_wrong",
         ),
+        pytest.param(
+            {
+                "src": "192.0.2.1",
+                "dst": "192.0.2.2",
+                "icmp_type": 0,
+                "icmp_code": 0,
+                "special": "short-wrong",
+            },
+            {
+                "returncode": 0,
+                "stdout": """\
+PATTERN: 0x01
+PING 192.0.2.2 (192.0.2.2): 56 data bytes
+63 bytes from: icmp_seq=0 ttl= time= ms
+wrong total length 83 instead of 84
+wrong data byte #54 should be 0x1 but was 0x0
+cp: xx xx xx xx xx xx xx xx
+	  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1
+	  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1
+	  1  1  1  1  1  1  1  1  1  1  1  1  1  1  0
+dp: xx xx xx xx xx xx xx xx
+	  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1
+	  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1
+	  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1
+
+--- 192.0.2.2 ping statistics ---
+1 packets transmitted, 1 packets received, 0.0% packet loss
+round-trip min/avg/max/stddev = /// ms
+""",
+                "stderr": "",
+                "redacted": True,
+            },
+            id="_0_0_special_short_wrong",
+        ),
     ]
 
     @pytest.mark.parametrize("pinger_kargs, expected", pinger_testdata)