[PATCH][SMB3] warn on confusing error scenario with sec=krb5

[Steve French]

    When mounting with Kerberos, users have been confused about the
    default error returned in scenarios in which either keyutils is
    not installed or the user did not properly acquire a krb5 ticket.
    Log a warning message in the case that "ENOKEY" is returned
    from the get_spnego_key upcall so that users can better understand
    why mount failed in those two cases.

    CC: Stable <stable at vger.kernel.org>
    Signed-off-by: Steve French <stfrench at microsoft.com>

diff --git a/fs/cifs/smb2pdu.c b/fs/cifs/smb2pdu.c
index 2f4cdd290c46..492688764004 100644
--- a/fs/cifs/smb2pdu.c
+++ b/fs/cifs/smb2pdu.c
@@ -1387,6 +1387,8 @@ SMB2_auth_kerberos(struct SMB2_sess_data *sess_data)
        spnego_key = cifs_get_spnego_key(ses);
        if (IS_ERR(spnego_key)) {
                rc = PTR_ERR(spnego_key);
+               if (rc == -ENOKEY)
+                       cifs_dbg(VFS, "Verify user has a krb5 ticket
and keyutils is installed\n");
                spnego_key = NULL;
                goto out;
        }


-- 
Thanks,

Steve