[PATCH net v2] net/tcp-ao: don't dereference NULL current_key/rnext_key

[Xiang Mei <xmei5@asu.edu>]

TCP_AO_DEL_KEY with del_async=1 is accepted in TCP_LISTEN and NULLs
current_key and rnext_key; tcp_ao_connect_init() clears them on a
reconnect.  Five readers dereference them without a check.

tcp_ao_time_wait() leaves tp->ao_info pointing at the tcp_ao_info it
hands the TIME_WAIT socket, and tcp_done() skips inet_csk_destroy_sock()
on the tcp_fin() FIN_WAIT2 path, so the full socket stays in TCP_CLOSE
with its fd open, sharing that object.  An unprivileged
connect(AF_UNSPEC) + listen() then clears rnext_key while the TIME_WAIT
socket reads it from softirq, and tcp_v4_timewait_ack() dereferences it.
The segment need not be authenticated: tcp_v4_rcv()'s do_time_wait: path
skips tcp_inbound_hash().

Check both fields and drop the segment when the key is gone; without one
no valid signature can be produced.  In tcp_inbound_ao_hash() this must
be a drop rather than a fallthrough to the keyid lookup, which would let
the peer pick the verification key that rnext_key pins.

This removes the dereferences only; the two sockets still share one
mutable tcp_ao_info, leaving snd_sne, lisn and sk_omem_alloc racy.  The
first Fixes: is where the unchecked read came from, not the sharing.

  Oops: general protection fault, probably for non-canonical address
    0xdffffc0000000010: 0000 [#1] SMP KASAN NOPTI
  KASAN: null-ptr-deref in range [0x0000000000000080-0x0000000000000087]
  RIP: 0010:tcp_v4_rcv (net/ipv4/tcp_ipv4.c:1055 net/ipv4/tcp_ipv4.c:2333)
  Call Trace:
   <IRQ>
   ip_protocol_deliver_rcu (net/ipv4/ip_input.c:207)
   ip_local_deliver (net/ipv4/ip_input.c:262)
   ip_rcv (net/ipv4/ip_input.c:612)
   __netif_receive_skb_one_core (net/core/dev.c:6264)
   process_backlog (net/core/dev.c:6728)
   net_rx_action (net/core/dev.c:8007)
   handle_softirqs (kernel/softirq.c:645)
   </IRQ>
  Kernel panic - not syncing: Fatal exception in interrupt

Fixes: decde2586b34 ("net/tcp: Add TCP-AO sign to twsk")
Fixes: 0a3a809089eb ("net/tcp: Verify inbound TCP-AO signed segments")
Cc: stable@vger.kernel.org
Reported-by: co+2c72469dbbec34af@bugs.sh
Closes: https://lore.kernel.org/all/YG9s0PiBKJZcXAKld3MToa1IVRJOUoKiaA57%40bugs.sh/
Signed-off-by: Xiang Mei <xmei5@asu.edu>
---
v2: drop the incomplete v1 fix; adding missing checks to avoid null-deref

 net/ipv4/tcp_ao.c   | 6 ++++++
 net/ipv4/tcp_ipv4.c | 4 ++++
 net/ipv6/tcp_ipv6.c | 2 ++
 3 files changed, 12 insertions(+)

diff --git a/net/ipv4/tcp_ao.c b/net/ipv4/tcp_ao.c
index bb7bbc20ba3f..9c2e5c8c8fe3 100644
--- a/net/ipv4/tcp_ao.c
+++ b/net/ipv4/tcp_ao.c
@@ -857,6 +857,8 @@ int tcp_ao_prepare_reset(const struct sock *sk, struct sk_buff *skb,
 			return -ENOENT;
 		*traffic_key = snd_other_key(*key);
 		rnext_key = READ_ONCE(ao_info->rnext_key);
+		if (!rnext_key)
+			return -ENOENT;
 		*keyid = rnext_key->rcvid;
 		*sne = tcp_ao_compute_sne(READ_ONCE(ao_info->snd_sne),
 					  snd_basis, seq);
@@ -1026,6 +1028,8 @@ tcp_inbound_ao_hash(struct sock *sk, const struct sk_buff *skb,
 		 * matching the rcvid in the mkt.
 		 */
 		key = READ_ONCE(info->rnext_key);
+		if (!key)
+			goto key_not_found;
 		if (key->rcvid != aoh->keyid) {
 			key = tcp_ao_established_key(sk, info, -1, aoh->keyid);
 			if (!key)
@@ -1045,6 +1049,8 @@ tcp_inbound_ao_hash(struct sock *sk, const struct sk_buff *skb,
 		if (err)
 			return err;
 		current_key = READ_ONCE(info->current_key);
+		if (!current_key)
+			return SKB_DROP_REASON_TCP_AOFAILURE;
 		/* Key rotation: the peer asks us to use new key (RNext) */
 		if (unlikely(aoh->rnext_keyid != current_key->sndid)) {
 			trace_tcp_ao_rnext_request(sk, skb, current_key->sndid,
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 9f053eb8b46e..93e073065b1b 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1052,6 +1052,10 @@ static void tcp_v4_timewait_ack(struct sock *sk, struct sk_buff *skb,
 		key.traffic_key = snd_other_key(key.ao_key);
 		key.sne = READ_ONCE(ao_info->snd_sne);
 		rnext_key = READ_ONCE(ao_info->rnext_key);
+		if (!rnext_key) {
+			inet_twsk_put(tw);
+			return;
+		}
 		key.rcv_next = rnext_key->rcvid;
 		key.type = TCP_KEY_AO;
 #else
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index df9c29eb5c1f..0fb75d139430 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -1182,6 +1182,8 @@ static void tcp_v6_timewait_ack(struct sock *sk, struct sk_buff *skb,
 		key.traffic_key = snd_other_key(key.ao_key);
 		/* rcv_next switches to our rcv_next */
 		rnext_key = READ_ONCE(ao_info->rnext_key);
+		if (!rnext_key)
+			goto out;
 		key.rcv_next = rnext_key->rcvid;
 		key.sne = READ_ONCE(ao_info->snd_sne);
 		key.type = TCP_KEY_AO;
-- 
2.43.0