[PATCH AUTOSEL 6.18-5.15] ksmbd: find bound sessions during reauthentication

[Sasha Levin <sashal@kernel.org>]

From: Namjae Jeon <linkinjeon@kernel.org>

[ Upstream commit faf8578c77f3d846aca9cd882c293e03eafcc6df ]

A session bound to an additional connection is stored in the session
channel list, but it is not added to that connection's local session table.
After the binding exchange completes, conn->binding is cleared.

A later SESSION_SETUP reauthentication on the bound channel only searches
the local session table. It fails to find the session and returns
STATUS_USER_SESSION_DELETED instead of processing authentication and
returning STATUS_LOGON_FAILURE for invalid credentials.

If the local lookup fails, look up the session globally and accept it only
when the current connection is registered in its channel list. This keeps
unbound connections from using the session while allowing reauthentication
on an established channel.

This fixes smb2.session.bind_invalid_auth.

Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

LLM Generated explanations, may be completely bogus:

The background `git branch -a --contains` check hung and was killed; it
didn’t change the backport analysis.

A quick rerun confirmed the SMB3 multichannel commit object exists in
this repo and the binding code landed via the 6.18-rc8 merge. The
verdict for **linux-6.18.y** stands: **YES** — a small, low-risk fix for
broken SMB3 multichannel reauthentication on bound channels.

 fs/smb/server/smb2pdu.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/fs/smb/server/smb2pdu.c b/fs/smb/server/smb2pdu.c
index 55ac0ee338dae..9394fd2605f3d 100644
--- a/fs/smb/server/smb2pdu.c
+++ b/fs/smb/server/smb2pdu.c
@@ -1863,6 +1863,13 @@ int smb2_sess_setup(struct ksmbd_work *work)
 	} else {
 		sess = ksmbd_session_lookup(conn,
 					    le64_to_cpu(req->hdr.SessionId));
+		if (!sess) {
+			sess = ksmbd_session_lookup_slowpath(le64_to_cpu(req->hdr.SessionId));
+			if (sess && !lookup_chann_list(sess, conn)) {
+				ksmbd_user_session_put(sess);
+				sess = NULL;
+			}
+		}
 		if (!sess) {
 			rc = -ENOENT;
 			goto out_err;
-- 
2.53.0