[PATCH net-next v3 2/5] 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.

Drivers that use on-device tx key storage need additional logic to delay
key deletion until after any in-flight users of the key have been
drained, so return -EOPNOTSUPP for now.

Signed-off-by: Daniel Zahka <daniel.zahka@gmail.com>
---
v3:
- move the replaced assoc to psd->stale_assocs, so a rotation
  racing with its free doesn't count the socket twice in stale-events
- document that the previous rx SPI also stops being accepted once
  its device key is rotated out
- drop the claim that the peer accepts both the old and new SPI
  after a tx rekey
- document tx rekey in the tx-assoc op doc in psp.yaml

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/netlink/specs/psp.yaml |  4 ++-
 Documentation/networking/psp.rst     |  5 +++-
 net/psp/psp_sock.c                   | 57 ++++++++++++++++++++++++++++++++----
 3 files changed, 58 insertions(+), 8 deletions(-)

diff --git a/Documentation/netlink/specs/psp.yaml b/Documentation/netlink/specs/psp.yaml
index d5713f5d1af7..f6af1a510d17 100644
--- a/Documentation/netlink/specs/psp.yaml
+++ b/Documentation/netlink/specs/psp.yaml
@@ -283,7 +283,9 @@ operations:
         post: psp-device-unlock
     -
       name: tx-assoc
-      doc: Add a PSP Tx association.
+      doc: |
+        Add a PSP Tx association.
+        If the socket already has a Tx association, rekey its Tx direction.
       attribute-set: assoc
       do:
         request:
diff --git a/Documentation/networking/psp.rst b/Documentation/networking/psp.rst
index fab797506b0a..43f222b38d3d 100644
--- a/Documentation/networking/psp.rst
+++ b/Documentation/networking/psp.rst
@@ -145,7 +145,8 @@ 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, using the same netlink calls as in connection setup.
+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
@@ -154,6 +155,8 @@ next Rx rekey, or until the device key it was derived from has been
 rotated out, 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.
+
 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
diff --git a/net/psp/psp_sock.c b/net/psp/psp_sock.c
index c1e38845f08c..d497f41c483e 100644
--- a/net/psp/psp_sock.c
+++ b/net/psp/psp_sock.c
@@ -280,6 +280,53 @@ 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);
+	list_move(&pas->assocs_list, &psd->stale_assocs);
+
+	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)
@@ -312,13 +359,11 @@ 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