[PATCH net-next v2 2/7] psp: support tx rekey operation

[Daniel Zahka <daniel.zahka@gmail.com>]

The tx rekey operation creates a new psp_assoc with the same rx state,
but with new tx state. The new association is spliced into the socket
with RCU to be used immediately in the tx path.

Signed-off-by: Daniel Zahka <daniel.zahka@gmail.com>
---
v2:
- place new assoc on pas->assocs list instead of psd->active assocs
  list
- reject tx rekey on SADB devices until deferred tx key deletion
  lands
---
 Documentation/networking/psp.rst | 26 +++++++++++++++++--
 net/psp/psp_sock.c               | 56 +++++++++++++++++++++++++++++++++++-----
 2 files changed, 74 insertions(+), 8 deletions(-)

diff --git a/Documentation/networking/psp.rst b/Documentation/networking/psp.rst
index 0f9b6b73f244..5c4e4215d906 100644
--- a/Documentation/networking/psp.rst
+++ b/Documentation/networking/psp.rst
@@ -140,14 +140,36 @@ The PSP assoc state of a socket is not reset when the connection is
 torn down. ``connect()`` on a socket that has PSP assoc state will
 return ``-EINVAL``.
 
+Rekeying
+--------
+
+A connection which has completed the exchange described above and is
+in the "PSP Full" state can be rekeyed in place without being torn
+down. The Tx and Rx directions are rekeyed separately using the same
+netlink calls as in connection setup.
+
+``rx-assoc`` allocates a new Rx key and SPI, which should be passed
+to the peer exactly as during the initial exchange. The SPI which was
+in use before the rekey remains acceptable on the socket until the
+next Rx rekey, so packets the peer sent before it learned the new SPI
+are still received.
+
+``tx-assoc`` installs a new Tx key, which takes effect immediately.
+The peer will accept data encrypted from the old and new SPI.
+
+A rekey is rejected with ``-EINVAL`` if it would change the PSP device
+or the PSP version of the association. It is rejected with ``-EBUSY``
+if the socket has not completed its initial exchange in both
+directions.
+
 Rotation notifications
 ----------------------
 
 The rotations of device key happen asynchronously and are usually
 performed by management daemons, not under application control.
 The PSP netlink family will generate a notification whenever keys
-are rotated. The applications are expected to re-establish connections
-before keys are rotated again.
+are rotated. Applications are expected to rekey their connections,
+as described above, before device keys are rotated again.
 
 Kernel implementation
 =====================
diff --git a/net/psp/psp_sock.c b/net/psp/psp_sock.c
index b5887171c84e..060149f3d72a 100644
--- a/net/psp/psp_sock.c
+++ b/net/psp/psp_sock.c
@@ -283,6 +283,52 @@ psp_sock_set_tx_key(struct sock *sk, struct psp_dev *psd, struct psp_assoc *pas,
 	return err;
 }
 
+static int
+psp_sock_tx_rekey(struct sock *sk, struct psp_dev *psd, struct psp_assoc *pas,
+		  struct psp_key_parsed *key, struct netlink_ext_ack *extack)
+{
+	struct psp_assoc *new;
+	int err;
+
+	if (psp_dev_has_sadb(psd)) {
+		NL_SET_ERR_MSG(extack, "Tx rekey not supported on this device");
+		return -EOPNOTSUPP;
+	}
+	if (!pas->peer_tx) {
+		NL_SET_ERR_MSG(extack, "Socket PSP state is not fully established");
+		return -EBUSY;
+	}
+
+	new = kzalloc_flex(*new, drv_data, psd->caps->assoc_drv_spc,
+			   GFP_KERNEL_ACCOUNT);
+	if (!new)
+		return -ENOMEM;
+
+	new->psd             = pas->psd;
+	new->dev_id          = pas->dev_id;
+	new->generation      = pas->generation;
+	new->version         = pas->version;
+	new->peer_tx         = 1;
+	new->prev_spi        = pas->prev_spi;
+	new->prev_generation = pas->prev_generation;
+	refcount_set(&new->refcnt, 1);
+	memcpy(&new->rx, &pas->rx, sizeof(new->rx));
+
+	err = psp_assoc_set_tx(psd, new, key, extack);
+	if (err) {
+		kfree(new);
+		return err;
+	}
+
+	psp_dev_get(new->psd);
+	list_add(&new->assocs_list, &pas->assocs_list);
+
+	rcu_assign_pointer(sk->psp_assoc, new);
+	psp_assoc_put(pas);
+
+	return 0;
+}
+
 int psp_sock_assoc_set_tx(struct sock *sk, struct psp_dev *psd,
 			  u32 version, struct psp_key_parsed *key,
 			  struct netlink_ext_ack *extack)
@@ -315,13 +361,11 @@ int psp_sock_assoc_set_tx(struct sock *sk, struct psp_dev *psd,
 		err = -EINVAL;
 		goto exit_unlock;
 	}
-	if (pas->tx.spi) {
-		NL_SET_ERR_MSG(extack, "Tx key already set");
-		err = -EBUSY;
-		goto exit_unlock;
-	}
+	if (pas->tx.spi)
+		err = psp_sock_tx_rekey(sk, psd, pas, key, extack);
+	else
+		err = psp_sock_set_tx_key(sk, psd, pas, key, extack);
 
-	err = psp_sock_set_tx_key(sk, psd, pas, key, extack);
 exit_unlock:
 	release_sock(sk);
 	return err;

-- 
2.52.0