smb2: Enforce sec= mount option

If the security type specified using a mount option is not supported,
the SMB2 session setup code changes the security type to RawNTLMSSP. We
should instead fail the mount and return an error.

The patch changes the code for SMB2 to make it similar to the code used
for SMB1. Like in SMB1, we now use the global security flags to select
the security method to be used when no security method is specified and
to return an error when the requested auth method is not available.

For SMB2, we also use ntlmv2 as a synonym for nltmssp.

Signed-off-by: Sachin Prabhu <sprabhu@redhat.com>
Acked-by: Pavel Shilovsky <pshilov@microsoft.com>
Acked-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <smfrench@gmail.com>

1 files changed, 33 insertions, 4 deletions

diff --git a/fs/cifs/smb2pdu.c b/fs/cifs/smb2pdu.c
index 2069431b32e3..7446496850a3 100644
--- a/fs/cifs/smb2pdu.c
+++ b/fs/cifs/smb2pdu.c
@@ -657,6 +657,28 @@ vneg_out:
 	return -EIO;
 }
 
+enum securityEnum
+smb2_select_sectype(struct TCP_Server_Info *server, enum securityEnum requested)
+{
+	switch (requested) {
+	case Kerberos:
+	case RawNTLMSSP:
+		return requested;
+	case NTLMv2:
+		return RawNTLMSSP;
+	case Unspecified:
+		if (server->sec_ntlmssp &&
+			(global_secflags & CIFSSEC_MAY_NTLMSSP))
+			return RawNTLMSSP;
+		if ((server->sec_kerberos || server->sec_mskerberos) &&
+			(global_secflags & CIFSSEC_MAY_KRB5))
+			return Kerberos;
+		/* Fallthrough */
+	default:
+		return Unspecified;
+	}
+}
+
 struct SMB2_sess_data {
 	unsigned int xid;
 	struct cifs_ses *ses;
@@ -1009,10 +1031,17 @@ out:
 static int
 SMB2_select_sec(struct cifs_ses *ses, struct SMB2_sess_data *sess_data)
 {
-	if (ses->sectype != Kerberos && ses->sectype != RawNTLMSSP)
-		ses->sectype = RawNTLMSSP;
+	int type;
+
+	type = smb2_select_sectype(ses->server, ses->sectype);
+	cifs_dbg(FYI, "sess setup type %d\n", type);
+	if (type == Unspecified) {
+		cifs_dbg(VFS,
+			"Unable to select appropriate authentication method!");
+		return -EINVAL;
+	}
 
-	switch (ses->sectype) {
+	switch (type) {
 	case Kerberos:
 		sess_data->func = SMB2_auth_kerberos;
 		break;
@@ -1020,7 +1049,7 @@ SMB2_select_sec(struct cifs_ses *ses, struct SMB2_sess_data *sess_data)
 		sess_data->func = SMB2_sess_auth_rawntlmssp_negotiate;
 		break;
 	default:
-		cifs_dbg(VFS, "secType %d not supported!\n", ses->sectype);
+		cifs_dbg(VFS, "secType %d not supported!\n", type);
 		return -EOPNOTSUPP;
 	}