[PATCH 5.15.y] ksmbd: reject non-VALID session in compound request branch

[Sasha Levin <sashal@kernel.org>]

From: Gil Portnoy <dddhkts1@gmail.com>

[ Upstream commit 609ca17d869d04ba249e32cdcbf13c0b1c66f43c ]

smb2_check_user_session() takes a shortcut for any operation that is not
the first in a COMPOUND request: it reuses work->sess (the session bound by
the first operation) and validates only the SessionId, then returns
"valid". It never re-checks work->sess->state == SMB2_SESSION_VALID, and a
SessionId of 0xFFFFFFFFFFFFFFFF (ULLONG_MAX, the MS-SMB2 related-operation
value) skips even the id comparison. The standalone path
(ksmbd_session_lookup_all() plus the SESSION_SETUP state machine) does
enforce the VALID state; the compound branch bypasses all of it.

A SESSION_SETUP carrying only an NTLM Type-1 (NtLmNegotiate) blob publishes
a fresh SMB2_SESSION_IN_PROGRESS session whose sess->user is still NULL
(->user is assigned later, by ntlm_authenticate()). Used as operation 1 of
a COMPOUND with operation 2 = TREE_CONNECT (related, SessionId=ULLONG_MAX,
\\host\IPC$), the tree-connect then runs on that IN_PROGRESS session and
reaches ksmbd_ipc_tree_connect_request(), which dereferences
user_name(sess->user) with sess->user == NULL (transport_ipc.c:687/701/704)
-> remote NULL-pointer dereference and a kernel Oops that wedges the ksmbd
worker for all clients.

Reject any non-first compound operation that lands on a session which is
not SMB2_SESSION_VALID, mirroring the validity the standalone lookup path
enforces. SESSION_SETUP itself legitimately runs on an IN_PROGRESS session,
but it is never carried as a non-first compound operation, so multi-leg
authentication is unaffected by this check.

Fixes: 5005bcb42191 ("ksmbd: validate session id and tree id in the compound request")
Cc: stable@vger.kernel.org
Signed-off-by: Gil Portnoy <dddhkts1@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>
---
 fs/ksmbd/smb2pdu.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/fs/ksmbd/smb2pdu.c b/fs/ksmbd/smb2pdu.c
index d029227f2ba616..496e1b50700d03 100644
--- a/fs/ksmbd/smb2pdu.c
+++ b/fs/ksmbd/smb2pdu.c
@@ -606,6 +606,11 @@ int smb2_check_user_session(struct ksmbd_work *work)
 					sess_id, work->sess->id);
 			return -EINVAL;
 		}
+		if (work->sess->state != SMB2_SESSION_VALID) {
+			pr_err("compound request on a non-valid session (state %d)\n",
+					work->sess->state);
+			return -EINVAL;
+		}
 		return 1;
 	}
 
-- 
2.53.0