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ksmbd: defer destroy_previous_session() until after NTLM authentication

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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.

Fixes: e2f34481b2 ("cifsd: add server-side procedures for SMB3")
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/linux-cifs/20260702155449.3639773-1-james_montgomery@disroot.org/
Signed-off-by: James Montgomery <james_montgomery@disroot.org>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
This commit is contained in:
James Montgomery 2026-07-03 15:26:41 -04:00 committed by Steve French
parent 5152c6d49e
commit c74801ee52
1 changed files with 4 additions and 5 deletions
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9
fs/smb/server/smb2pdu.c
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@ -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