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Subject: Re: [RFC,PATCH v2] efi: Add support for a UEFI variable filesystem
From: Matt Fleming <matt.fleming@intel.com>
To: Jeremy Kerr <jeremy.kerr@canonical.com>
Cc: linux-kernel@vger.kernel.org, Matthew Garrett <mjg@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Matt Domsch <Matt_Domsch@Dell.com>,
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Date: Thu, 06 Sep 2012 15:30:51 +0100
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(Cc'ing Peter Jones who wrote a auth deletion patch for efivars)

On Thu, 2012-09-06 at 22:23 +0800, Jeremy Kerr wrote:
> Hi Matt,
> 
> > Am I correct in thinking that this filesystem doesn't handle deletion of
> > authenticated variables?
> 
> Unless I'm missing something, this should work fine; we just pass the 
> EFI_VARIABLE_AUTHENTICATION_2 descriptor (with the usual attribute 
> header), but no data following the descriptor.

I think this is the problematic chunk of code,

static int efivars_unlink(struct inode *dir, struct dentry *dentry)             
{                                                                               
        struct efivar_entry *var = dentry->d_inode->i_private;                  
        struct efivars *efivars = var->efivars;                                 
        efi_status_t status;                                                    
                                                                                
        spin_lock(&efivars->lock);                                              
                                                                                
        status = efivars->ops->set_variable(var->var.VariableName,              
                                            &var->var.VendorGuid,               
                                            0, 0, NULL);                        

For deleting authenticated variables Attributes, DataSize and Data need
to be non-zero. I think DataSize == AuthInfo descriptor. Peter?