Validate crypto-NAK's

bk: 56b42514rgZyUCPCWq2Uyhw4BWUpSg

diff --git a/ChangeLog b/ChangeLog
index c70fe8fc563cf0a16def01a652b989e8bc667f06..3bb8f305a102ce9a68ff61c6e18b46f1b33635e6 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,4 @@
+* [Bug 3007] Validate crypto-NAKs
 ---
 
 * [Bug 2994] Systems with HAVE_SIGNALED_IO fail to compile. perlinger@ntp.org

diff --git a/include/ntp.h b/include/ntp.h
index 6a4e9aa6f386909a078296b3a6dcc1508b5ad96f..9d7407d7cf8c762d9f0b0cf397b3b1f78941d2dc 100644 (file)
--- a/include/ntp.h
+++ b/include/ntp.h
@@ -391,6 +391,7 @@ struct peer {
        u_long  received;       /* packets received */
        u_long  processed;      /* packets processed */
        u_long  badauth;        /* bad authentication (TEST5) */
+       u_long  badNAK;         /* invalid crypto-NAK */
        u_long  bogusorg;       /* bogus origin (TEST2, TEST3) */
        u_long  oldpkt;         /* old duplicate (TEST1) */
        u_long  seldisptoolarge; /* bad header (TEST6, TEST7) */
@@ -545,6 +546,7 @@ struct pkt {
        l_fp    rec;            /* receive time stamp */
        l_fp    xmt;            /* transmit time stamp */
 
+#define        MIN_V4_PKT_LEN  (12 * sizeof(u_int32)) /* min header length */
 #define        LEN_PKT_NOMAC   (12 * sizeof(u_int32)) /* min header length */
 #define MIN_MAC_LEN    (1 * sizeof(u_int32))   /* crypto_NAK */
 #define MAX_MD5_LEN    (5 * sizeof(u_int32))   /* MD5 */

diff --git a/ntpd/ntp_proto.c b/ntpd/ntp_proto.c
index ad454099f8b924a16ca84cf3fd162a1d8ab58e61..6d6658b314db589d7202808ab4f7e3d9c8459fe8 100644 (file)
--- a/ntpd/ntp_proto.c
+++ b/ntpd/ntp_proto.c
@@ -50,6 +50,12 @@ enum kiss_codes {
        UNKNOWNKISS                     /* Unknown Kiss Code */
 };
 
+enum nak_error_codes {
+       NONAK,                          /* No NAK seen */
+       INVALIDNAK,                     /* NAK cannot be used */
+       VALIDNAK                        /* NAK is valid */
+};
+
 /*
  * traffic shaping parameters
  */
@@ -252,6 +258,63 @@ kiss_code_check(
        }
 }
 
+/* 
+ * Check that NAK is valid
+ */
+BOOL
+valid_NAK(
+         struct peer *peer,
+         struct recvbuf *rbufp,
+         u_char hismode
+         )
+{
+       int base_packet_length = MIN_V4_PKT_LEN;
+       int remainder_size;
+       struct pkt *rpkt;
+       int keyid;
+
+       /*
+        * Check to see if there is something beyond the basic packet
+        */
+       if (rbufp->recv_length == base_packet_length) {
+               return NONAK;
+       }
+
+       remainder_size = rbufp->recv_length - base_packet_length;
+       /*
+        * Is this a potential NAK?
+        */
+       if (remainder_size != 4) {
+               return NONAK;
+       }
+
+       /*
+        * Only server responses can contain NAK's
+        */
+
+       if (hismode != MODE_SERVER) {
+               return (INVALIDNAK);
+       }
+
+       /* 
+        * Make sure that the extra field in the packet is all zeros
+        */
+       rpkt = &rbufp->recv_pkt;
+       keyid = ntohl(((u_int32 *)rpkt)[base_packet_length / 4]);
+       if (keyid != 0) {
+               return (INVALIDNAK);
+       }
+
+       /* 
+        * Only valid if peer uses a key
+        */
+       if (peer->keyid > 0 || peer->flags & FLAG_SKEY) {
+               return (VALIDNAK);
+       }
+       else {
+               return (INVALIDNAK);
+       }
+}
 
 /*
  * transmit - transmit procedure called by poll timeout
@@ -493,6 +556,7 @@ receive(
        int     has_mac;                /* length of MAC field */
        int     authlen;                /* offset of MAC field */
        int     is_authentic = 0;       /* cryptosum ok */
+       int     crypto_nak_test;        /* result of crypto-NAK check */
        int     retcode = AM_NOMATCH;   /* match code */
        keyid_t skeyid = 0;             /* key IDs */
        u_int32 opcode = 0;             /* extension field opcode */
@@ -617,6 +681,7 @@ receive(
         * extension field is present, so we subtract the length of the
         * field and go around again.
         */
+
        authlen = LEN_PKT_NOMAC;
        has_mac = rbufp->recv_length - authlen;
        while (has_mac > 0) {
@@ -767,6 +832,17 @@ receive(
         * is zero, acceptable outcomes of y are NONE and OK. If x is
         * one, the only acceptable outcome of y is OK.
         */
+       crypto_nak_test = valid_NAK(peer, rbufp, hismode);
+
+       /*
+        * Drop any invalid crypto-NAKs
+        */
+       if (crypto_nak_test == INVALIDNAK) {
+               peer->badNAK++;
+               msyslog(LOG_ERR, "crypto-NAK error at %ld %s<-%s", 
+                       current_time, stoa(dstadr_sin), stoa(&rbufp->recv_srcadr));
+               return;
+       }
 
        if (has_mac == 0) {
                restrict_mask &= ~RES_MSSNTP;
@@ -777,7 +853,7 @@ receive(
                            authlen,
                            ntohl(pkt->org.l_ui), ntohl(pkt->org.l_uf),
                            ntohl(pkt->xmt.l_ui), ntohl(pkt->xmt.l_uf)));
-       } else if (has_mac == 4) {
+       } else if (crypto_nak_test == VALIDNAK) {
                restrict_mask &= ~RES_MSSNTP;
                is_authentic = AUTH_CRYPTO; /* crypto-NAK */
                DPRINTF(2, ("receive: at %ld %s<-%s mode %d/%s:%s keyid %08x len %d auth %d org %#010x.%08x xmt %#010x.%08x MAC4\n",
@@ -1507,7 +1583,7 @@ receive(
         * client packet. The server might have just changed keys. Clear
         * the association and restart the protocol.
         */
-       if (is_authentic == AUTH_CRYPTO) {
+       if (crypto_nak_test == VALIDNAK) {
                report_event(PEVNT_AUTH, peer, "crypto_NAK");
                peer->flash |= TEST5;           /* bad auth */
                peer->badauth++;