ksmbd: decrypt requests from expired encrypted sessions

Previous-session replacement marks the old session expired but retains its
SMB3 encryption key. An in-flight encrypted request can still arrive on
that connection. Rejecting the expired session before decryption made ksmbd
treat the request as a key failure and abort the transport, causing
reconnect failures.

Allow key lookup for expired sessions that have encryption enabled. Keep
the session reference during validation so the normal
STATUS_USER_SESSION_DELETED response is encrypted with the old key. The
session remains expired and no command is executed.

Fixes: fa9415d4024f ("ksmbd: mark SMB2_SESSION_EXPIRED to session when destroying previous session")
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>

2 files changed, 14 insertions, 6 deletions

diff --git a/fs/smb/server/auth.c b/fs/smb/server/auth.c
index bcd371f5550d..78491b20897e 100644
--- a/fs/smb/server/auth.c
+++ b/fs/smb/server/auth.c
@@ -724,15 +724,15 @@ static int ksmbd_get_encryption_key(struct ksmbd_work *work, __u64 ses_id,
 		sess = work->sess;
 	else {
 		/*
-		 * An encrypted SESSION_SETUP request may reauthenticate an expired
-		 * Kerberos session.  Keep using the established decryption key so
-		 * that the command can reach the session setup handler. Other
-		 * commands are rejected there with STATUS_NETWORK_SESSION_EXPIRED.
+		 * A previous-session replacement leaves the old encryption key in
+		 * place.  Use it to authenticate an encrypted request, then let
+		 * session validation reject the expired session.  This preserves the
+		 * encrypted STATUS_USER_SESSION_DELETED response without reviving
+		 * the session.
 		 */
 		sess = ksmbd_session_lookup_all_states(work->conn, ses_id);
 		if (sess && sess->state != SMB2_SESSION_VALID &&
-		    (sess->state != SMB2_SESSION_EXPIRED ||
-		     !sess->kerberos_expiry)) {
+		    (sess->state != SMB2_SESSION_EXPIRED || !sess->enc)) {
 			ksmbd_user_session_put(sess);
 			sess = NULL;
 		}
diff --git a/fs/smb/server/smb2pdu.c b/fs/smb/server/smb2pdu.c
index ade16532a8c1..8d06c934f24f 100644
--- a/fs/smb/server/smb2pdu.c
+++ b/fs/smb/server/smb2pdu.c
@@ -1012,6 +1012,14 @@ int smb2_check_user_session(struct ksmbd_work *work)
 				1 : -EKEYEXPIRED;
 		}
 		if (work->sess->state != SMB2_SESSION_VALID) {
+			/*
+			 * Keep the reference for an encrypted request so the caller can
+			 * return STATUS_USER_SESSION_DELETED encrypted with the old key.
+			 */
+			if (work->encrypted &&
+			    work->sess->state == SMB2_SESSION_EXPIRED &&
+			    work->sess->enc)
+				return -ENOENT;
 			ksmbd_user_session_put(work->sess);
 			work->sess = NULL;
 			return -ENOENT;