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if_ovpn: ensure we never re-use sequence numbers

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if_ovpn already notified userpsace when there was a risk of sequence
number re-use, but it trusted userspace to actually rotate the key.

Convert the internal sequence number counter to 64 bits so we can detect
overflows and then refuse to send packets.

Event:		BSDCan 2023
Reviewed by:	Leon Dang <ldang@netgate.com>
Sponsored by:	Rubicon Communications, LLC ("Netgate")
Differential Revision:	https://reviews.freebsd.org/D40187
This commit is contained in:
Kristof Provost 2023-05-20 19:43:49 +02:00
parent c4a32455d9
commit 81877287a9
1 changed files with 18 additions and 4 deletions
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22
sys/net/if_ovpn.c
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@ -93,7 +93,7 @@ struct ovpn_kkey_dir {
* strictly higher than this.
*/
uint32_t rx_seq;
uint32_t tx_seq;
uint64_t tx_seq;
/* Seen packets, relative to rx_seq. bit(0) will always be 0. */
uint64_t rx_window;
@ -1830,6 +1830,7 @@ ovpn_transmit_to_peer(struct ifnet *ifp, struct mbuf *m,
struct ovpn_softc *sc;
struct cryptop *crp;
uint32_t af, seq;
uint64_t seq64;
size_t len, ovpn_hdr_len;
int tunnel_len;
int ret;
@ -1873,11 +1874,24 @@ ovpn_transmit_to_peer(struct ifnet *ifp, struct mbuf *m,
ohdr->opcode |= key->peerid;
ohdr->opcode = htonl(ohdr->opcode);
seq = atomic_fetchadd_32(&peer->keys[OVPN_KEY_SLOT_PRIMARY].encrypt->tx_seq, 1);
if (seq == OVPN_SEQ_ROTATE)
seq64 = atomic_fetchadd_64(&peer->keys[OVPN_KEY_SLOT_PRIMARY].encrypt->tx_seq, 1);
if (seq64 == OVPN_SEQ_ROTATE) {
ovpn_notify_key_rotation(sc, peer);
} else if (seq64 > UINT32_MAX) {
/* We've wrapped, give up on this packet. */
if (_ovpn_lock_trackerp != NULL)
OVPN_RUNLOCK(sc);
OVPN_COUNTER_ADD(sc, nomem_data_pkts_out, 1);
seq = htonl(seq);
/* Let's avoid (very unlikely, but still) wraparounds of the
* 64-bit counter taking us back to 0. */
atomic_set_64(&peer->keys[OVPN_KEY_SLOT_PRIMARY].encrypt->tx_seq,
UINT32_MAX);
return (ENOBUFS);
}
seq = htonl(seq64 & UINT32_MAX);
ohdr->seq = seq;
OVPN_PEER_COUNTER_ADD(peer, pkt_out, 1);