[PATCH 6.12 141/244] ksmbd: do not expire session on binding failure

Greg Kroah-Hartman
2026-03-31T16:53:19Z

From: Hyunwoo Kim <imv4bel@gmail.com>

commit 9bbb19d21ded7d78645506f20d8c44895e3d0fb9 upstream.

When a multichannel session binding request fails (e.g. wrong password),
the error path unconditionally sets sess->state = SMB2_SESSION_EXPIRED.
However, during binding, sess points to the target session looked up via
ksmbd_session_lookup_slowpath() -- which belongs to another connection's
user. This allows a remote attacker to invalidate any active session by
simply sending a binding request with a wrong password (DoS).

Fix this by skipping session expiration when the failed request was
a binding attempt, since the session does not belong to the current
connection. The reference taken by ksmbd_session_lookup_slowpath() is
still correctly released via ksmbd_user_session_put().

Cc: stable@vger.kernel.org
Signed-off-by: Hyunwoo Kim <imv4bel@gmail.com>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/smb/server/smb2pdu.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)

--- a/fs/smb/server/smb2pdu.c
+++ b/fs/smb/server/smb2pdu.c
@@ -1945,8 +1945,14 @@ out_err:
if (sess->user && sess->user->flags & KSMBD_USER_FLAG_DELAY_SESSION)
try_delay = true;

- sess->last_active = jiffies;
- sess->state = SMB2_SESSION_EXPIRED;
+ /*
+ * For binding requests, session belongs to another
+ * connection. Do not expire it.
+ */
+ if (!(req->Flags & SMB2_SESSION_REQ_FLAG_BINDING)) {
+ sess->last_active = jiffies;
+ sess->state = SMB2_SESSION_EXPIRED;
+ }
ksmbd_user_session_put(sess);
work->sess = NULL;
if (try_delay) {