[PATCH v6 4/8] ksmbd: refuse a binding request on a connection that is already a channel

[Michail Andreas Michalopoulos <mike.michalo@gmail.com>]

smb2_sess_setup() refuses a binding request for a session that the
connection already uses, but is_ksmbd_session_in_connection() only
knows the sessions created on the connection, not the ones it was bound
to as a channel. A connection that is already a channel of a session
can therefore bind to it again. The new binding legs are verified and
signed with the session key at that connection's MessageIds, and on
completion generate_signingkey() replaces the channel's signing key,
while register_session_channel() keeps the old channel entry.

Refuse such a request with STATUS_REQUEST_NOT_ACCEPTED, as MS-SMB2
3.3.5.5 does for a session that is already in Connection.SessionTable,
which a binding adds the session to (3.3.5.5.3).

An AI assistant was used to draft the patch and as an independent
reviewer.

Fixes: f5a544e3bab7 ("ksmbd: add support for SMB3 multichannel")
Cc: stable@vger.kernel.org
Signed-off-by: Michail Andreas Michalopoulos <mike.michalo@gmail.com>
---
 fs/smb/server/smb2pdu.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/smb/server/smb2pdu.c b/fs/smb/server/smb2pdu.c
index a15dd200645bb..186a497f83c62 100644
--- a/fs/smb/server/smb2pdu.c
+++ b/fs/smb/server/smb2pdu.c
@@ -2765,7 +2765,9 @@ int smb2_sess_setup(struct ksmbd_work *work)
 			goto out_err;
 		}
 
-		if (is_ksmbd_session_in_connection(conn, sess_id)) {
+		/* This connection must not already be using the session */
+		if (is_ksmbd_session_in_connection(conn, sess_id) ||
+		    lookup_chann_list(sess, conn)) {
 			rc = -EACCES;
 			goto out_err;
 		}
-- 
2.43.0