From 66576f9903cc166072901673ff1e673fa2e29611 Mon Sep 17 00:00:00 2001 From: Steffan Karger Date: Thu, 11 May 2017 23:13:41 +0200 Subject: [PATCH] Drop packets instead of assert out if packet id rolls over (CVE-2017-7479) Previously, if a mode was selected where packet ids are not allowed to roll over, but renegotiation does not succeed for some reason (e.g. no password entered in time, certificate expired or a malicious peer that refuses the renegotiaion on purpose) we would continue to use the old keys. Until the packet ID would roll over and we would ASSERT() out. Given that this can be triggered on purpose by an authenticated peer, this is a fix for an authenticated remote DoS vulnerability. An attack is rather inefficient though; a peer would need to get us to send 2^32 packets (min-size packet is IP+UDP+OPCODE+PID+TAG (no payload), results in (20+8+1+4+16)*2^32 bytes, or approx. 196 GB). This is a fix for finding 5.2 from the OSTIF / Quarkslab audit. This patch was cherry-picked from b727643c (release/2.3). CVE: 2017-7479 Signed-off-by: Steffan Karger Acked-by: Gert Doering Message-Id: <1494537221-12050-3-git-send-email-steffan@karger.me> URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg14645.html Signed-off-by: Gert Doering --- crypto.c | 18 +++++++++++++----- packet_id.c | 22 ++++++++++++++++------ packet_id.h | 1 + 3 files changed, 30 insertions(+), 11 deletions(-) diff --git a/crypto.c b/crypto.c index b7b2f018..b1a8a029 100644 --- a/crypto.c +++ b/crypto.c @@ -117,9 +117,11 @@ openvpn_encrypt (struct buffer *buf, struct buffer work, prng_bytes (iv_buf, iv_size); /* Put packet ID in plaintext buffer or IV, depending on cipher mode */ - if (opt->packet_id) + if (opt->packet_id + && !packet_id_write (&opt->packet_id->send, buf, BOOL_CAST (opt->flags & CO_PACKET_ID_LONG_FORM), true)) { - ASSERT (packet_id_write (&opt->packet_id->send, buf, BOOL_CAST (opt->flags & CO_PACKET_ID_LONG_FORM), true)); + msg (D_CRYPT_ERRORS, "ENCRYPT ERROR: packet ID roll over"); + goto err; } } else if (mode == EVP_CIPH_CFB_MODE || mode == EVP_CIPH_OFB_MODE) @@ -131,7 +133,11 @@ openvpn_encrypt (struct buffer *buf, struct buffer work, memset (iv_buf, 0, iv_size); buf_set_write (&b, iv_buf, iv_size); - ASSERT (packet_id_write (&opt->packet_id->send, &b, true, false)); + if (!packet_id_write (&opt->packet_id->send, &b, true, false)) + { + msg (D_CRYPT_ERRORS, "ENCRYPT ERROR: packet ID roll over"); + goto err; + } } else /* We only support CBC, CFB, or OFB modes right now */ { @@ -187,9 +193,11 @@ openvpn_encrypt (struct buffer *buf, struct buffer work, } else /* No Encryption */ { - if (opt->packet_id) + if (opt->packet_id + && !packet_id_write (&opt->packet_id->send, buf, BOOL_CAST (opt->flags & CO_PACKET_ID_LONG_FORM), true)) { - ASSERT (packet_id_write (&opt->packet_id->send, buf, BOOL_CAST (opt->flags & CO_PACKET_ID_LONG_FORM), true)); + msg (D_CRYPT_ERRORS, "ENCRYPT ERROR: packet ID roll over"); + goto err; } work = *buf; } diff --git a/packet_id.c b/packet_id.c index d1900744..a579726f 100644 --- a/packet_id.c +++ b/packet_id.c @@ -248,27 +248,37 @@ packet_id_read (struct packet_id_net *pin, struct buffer *buf, bool long_form) return true; } -static void +static bool packet_id_send_update(struct packet_id_send *p, bool long_form) { if (!p->time) { p->time = now; } - p->id++; - if (!p->id) + if (p->id == PACKET_ID_MAX) { - ASSERT(long_form); + /* Packet ID only allowed to roll over if using long form and time has + * moved forward since last roll over. + */ + if (!long_form || now <= p->time) + { + return false; + } p->time = now; - p->id = 1; + p->id = 0; } + p->id++; + return true; } bool packet_id_write (struct packet_id_send *p, struct buffer *buf, bool long_form, bool prepend) { - packet_id_send_update(p, long_form); + if (!packet_id_send_update(p, long_form)) + { + return false; + } const packet_id_type net_id = htonpid(p->id); const net_time_t net_time = htontime(p->time); diff --git a/packet_id.h b/packet_id.h index 59b7a7b0..7d70840b 100644 --- a/packet_id.h +++ b/packet_id.h @@ -50,6 +50,7 @@ * to for network transmission. */ typedef uint32_t packet_id_type; +#define PACKET_ID_MAX UINT32_MAX typedef uint32_t net_time_t; /*