Re: [PATCH] Fix guest smb3.1.1 mounts to Samba

[Steve French <smfrench@gmail.com>]

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Version 2 of patch added additional check that it is not krb5 mount
when username is null


On Fri, Mar 22, 2019 at 8:01 PM Steve French <smfrench@gmail.com> wrote:
>
> Add to Ronnie's patch check for null user so we can handle guest
> mounts for 3.1.1 to Samba as well
>
>
>
> --
> Thanks,
>
> Steve



-- 
Thanks,

Steve

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From 49bc93dc3371b9068e1c973f5169ab96c068a787 Mon Sep 17 00:00:00 2001
From: Steve French <stfrench@microsoft.com>
Date: Fri, 22 Mar 2019 22:31:17 -0500
Subject: [PATCH] SMB3: Fix SMB3.1.1 guest mounts to Samba

Workaround problem with Samba responses to SMB3.1.1
null user (guest) mounts.  The server doesn't set the
expected flag in the session setup response so we have
to do a similar check to what is done in smb3_validate_negotiate
where we also check if the user is a null user (but not sec=krb5
since username might not be passed in on mount for Kerberos case).

Note that the commit below tightened the conditions and forced signing
for the SMB2-TreeConnect commands as per MS-SMB2.
However, this should only apply to normal user sessions and not for
cases where there is no user (even if server forgets to set the flag
in the response) since we don't have anything useful to sign with.
This is especially important now that the more secure SMB3.1.1 protocol
is in the default dialect list.

An earlier patch ("cifs: allow guest mounts to work for smb3.11") fixed
the guest mounts to Windows.

    Fixes: 6188f28bf608 ("Tree connect for SMB3.1.1 must be signed for non-encrypted shares")

Reviewed-by: Ronnie Sahlberg <lsahlber@redhat.com>
CC: Stable <stable@vger.kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
---
 fs/cifs/smb2pdu.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/cifs/smb2pdu.c b/fs/cifs/smb2pdu.c
index 8e4a1da95418..21ac19ff19cb 100644
--- a/fs/cifs/smb2pdu.c
+++ b/fs/cifs/smb2pdu.c
@@ -1631,10 +1631,13 @@ SMB2_tcon(const unsigned int xid, struct cifs_ses *ses, const char *tree,
 	/*
 	 * 3.11 tcon req must be signed if not encrypted. See MS-SMB2 3.2.4.1.1
 	 * unless it is guest or anonymous user. See MS-SMB2 3.2.5.3.1
+	 * (Samba servers don't always set the flag so also check if null user)
 	 */
 	if ((ses->server->dialect == SMB311_PROT_ID) &&
 	    !smb3_encryption_required(tcon) &&
-	    !(ses->session_flags & (SMB2_SESSION_FLAG_IS_GUEST|SMB2_SESSION_FLAG_IS_NULL)))
+	    !(ses->session_flags &
+		    (SMB2_SESSION_FLAG_IS_GUEST|SMB2_SESSION_FLAG_IS_NULL)) &&
+	    ((ses->user_name != NULL) || (ses->sectype == Kerberos)))
 		req->sync_hdr.Flags |= SMB2_FLAGS_SIGNED;
 
 	memset(&rqst, 0, sizeof(struct smb_rqst));
-- 
2.17.1