FAILED: patch "[PATCH] ksmbd: defer destroy_previous_session() until after NTLM" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x c74801ee524f477c174a1899782b6c3b6918d407
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026072903-union-lagging-6c3f@gregkh' --subject-prefix 'PATCH 5.15.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From c74801ee524f477c174a1899782b6c3b6918d407 Mon Sep 17 00:00:00 2001
From: James Montgomery <[email protected]>
Date: Fri, 3 Jul 2026 15:26:41 -0400
Subject: [PATCH] ksmbd: defer destroy_previous_session() until after NTLM
authentication

In ntlm_authenticate(), destroy_previous_session() is called using a user pointer resolved from the client-supplied NTLM blob username field before the NTLMv2 response is validated. An authenticated attacker can set the NTLM blob username to match a victim account and set PreviousSessionId to the victim's session ID; destroy_previous_session() destroys the victim's session while ksmbd_decode_ntlmssp_auth_blob() subsequently rejects the request with -EPERM.

Move destroy_previous_session() and the prev_id assignment to after ksmbd_decode_ntlmssp_auth_blob() returns success and use sess->user rather than the pre-authentication lookup result. This matches the ordering already used by krb5_authenticate(), where destroy_previous_session() is called only after ksmbd_krb5_authenticate() returns success.

index d54b714cc36c..c1ba5e01aa7f 100644
@@ -1717,11 +1717,6 @@ static int ntlm_authenticate(struct ksmbd_work *work,
 		return -EPERM;
 	}
 
-	/* Check for previous session */
-	prev_id = le64_to_cpu(req->PreviousSessionId);
-	if (prev_id && prev_id != sess->id)
-		destroy_previous_session(conn, user, prev_id);
-
 	if (sess->state == SMB2_SESSION_VALID) {
 		/*
 		 * Reuse session if anonymous try to connect

@@ -1761,6 +1756,10 @@ static int ntlm_authenticate(struct ksmbd_work *work,
 		}
 	}
 
+	prev_id = le64_to_cpu(req->PreviousSessionId);
+	if (prev_id && prev_id != sess->id)
+		destroy_previous_session(conn, sess->user, prev_id);
+
 	/*
 	 * If session state is SMB2_SESSION_VALID, We can assume
 	 * that it is reauthentication. And the user/password

From: James Montgomery <[email protected]>

[ Upstream commit c74801ee524f477c174a1899782b6c3b6918d407 ]

In ntlm_authenticate(), destroy_previous_session() is called using a user pointer resolved from the client-supplied NTLM blob username field before the NTLMv2 response is validated. An authenticated attacker can set the NTLM blob username to match a victim account and set PreviousSessionId to the victim's session ID; destroy_previous_session() destroys the victim's session while ksmbd_decode_ntlmssp_auth_blob() subsequently rejects the request with -EPERM.

Move destroy_previous_session() and the prev_id assignment to after ksmbd_decode_ntlmssp_auth_blob() returns success and use sess->user rather than the pre-authentication lookup result. This matches the ordering already used by krb5_authenticate(), where destroy_previous_session() is called only after ksmbd_krb5_authenticate() returns success.

---
 fs/ksmbd/smb2pdu.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

index f7eeb79be48ab..f012b85e1d0d9 100644
@@ -1495,11 +1495,6 @@ static int ntlm_authenticate(struct ksmbd_work *work,
 		return -EPERM;
 	}
 
-	/* Check for previous session */
-	prev_id = le64_to_cpu(req->PreviousSessionId);
-	if (prev_id && prev_id != sess->id)
-		destroy_previous_session(conn, user, prev_id);
-
 	if (sess->state == SMB2_SESSION_VALID) {
 		/*
 		 * Reuse session if anonymous try to connect

@@ -1537,6 +1532,10 @@ static int ntlm_authenticate(struct ksmbd_work *work,
 		}
 	}
 
+	prev_id = le64_to_cpu(req->PreviousSessionId);
+	if (prev_id && prev_id != sess->id)
+		destroy_previous_session(conn, sess->user, prev_id);
+
 	/*
 	 * If session state is SMB2_SESSION_VALID, We can assume
 	 * that it is reauthentication. And the user/password

2.53.0