ksmbd: reset rcount per connection in ksmbd_conn_wait_idle_sess_id()

[ Upstream commit def036e ]

rcount is intended to be connection-specific: 2 for curr_conn, 1 for
every other connection sharing the same session.  However, it is
initialised only once before the hash iteration and is never reset.
After the loop visits curr_conn, later sibling connections are also
checked against rcount == 2, so a sibling with req_running == 1 is
incorrectly treated as idle.  This makes the outcome depend on the
hash iteration order: whether a given sibling is checked against the
loose (< 2) or the strict (< 1) threshold is decided by whether it
happens to be visited before or after curr_conn.

The function's contract is "wait until every connection sharing this
session is idle" so that destroy_previous_session() can safely tear
the session down.  The latched rcount violates that contract and
reopens the teardown race window the wait logic was meant to close:
destroy_previous_session() may proceed before sibling channels have
actually quiesced, overlapping session teardown with in-flight work
on those connections.

Recompute rcount inside the loop so each connection is compared
against its own threshold regardless of iteration order.

This is a code-inspection fix for an iteration-order-dependent logic
error; a targeted reproducer would require SMB3 multichannel with
in-flight work on a sibling channel landing after curr_conn in hash
order, which is not something that can be triggered reliably.

Fixes: 76e98a1 ("ksmbd: fix race condition between destroy_previous_session() and smb2 operations()")
Cc: stable@vger.kernel.org
Signed-off-by: DaeMyung Kang <charsyam@gmail.com>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: charsyam

fs/smb/server/connection.c

@@ -180,7 +180,7 @@ int ksmbd_conn_wait_idle_sess_id(struct ksmbd_conn *curr_conn, u64 sess_id)
 {
 	struct ksmbd_conn *conn;
 	int rc, retry_count = 0, max_timeout = 120;
-	int rcount = 1, bkt;
+	int rcount, bkt;
 
 retry_idle:
 	if (retry_count >= max_timeout)
@@ -189,8 +189,7 @@ int ksmbd_conn_wait_idle_sess_id(struct ksmbd_conn *curr_conn, u64 sess_id)
 	down_read(&conn_list_lock);
 	hash_for_each(conn_list, bkt, conn, hlist) {
 		if (conn->binding || xa_load(&conn->sessions, sess_id)) {
-			if (conn == curr_conn)
-				rcount = 2;
+			rcount = (conn == curr_conn) ? 2 : 1;
 			if (atomic_read(&conn->req_running) >= rcount) {
 				rc = wait_event_timeout(conn->req_running_q,
 					atomic_read(&conn->req_running) < rcount,