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Subject: Re: [PATCH 1/2] fs/efivarfs: restrict inode permissions
To:     Joe Konno <joe.konno@linux.intel.com>, linux-efi@vger.kernel.org,
        linux-kernel@vger.kernel.org
Cc:     ard.biesheuvel@linaro.org, matthew.garrett@nebula.com,
        jk@ozlabs.org, ak@linux.intel.com, tony.luck@intel.com
References: <20180215182208.35003-1-joe.konno@linux.intel.com>
 <20180215182208.35003-2-joe.konno@linux.intel.com>
From:   Andy Lutomirski <luto@kernel.org>
Message-ID: <6680a760-eb30-4daf-2dad-a9628f1c15a8@kernel.org>
Date:   Tue, 20 Feb 2018 11:18:57 -0800
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On 02/15/2018 10:22 AM, Joe Konno wrote:
> From: Joe Konno <joe.konno@intel.com>
> 
> Efivarfs nodes are created with group and world readable permissions.
> Reading certain EFI variables trigger SMIs. So, this is a potential DoS
> surface.
> 
> Make permissions more restrictive-- only the owner may read or write to
> created inodes.
> 
> Suggested-by: Andi Kleen <ak@linux.intel.com>
> Reported-by: Tony Luck <tony.luck@intel.com>
> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> Cc: Matthew Garrett <matthew.garrett@nebula.com>
> Cc: Jeremy Kerr <jk@ozlabs.org>
> Cc: linux-efi@vger.kernel.org
> Cc: stable@vger.kernel.org
> Signed-off-by: Joe Konno <joe.konno@intel.com>

The discussion in this thread has gone on too long, so:

Acked-by: Andy Lutomirski <luto@kernel.org>

And yes, this patch will break a couple of minor usecases, but IMO those 
usecases deserve to break.

> ---
>   fs/efivarfs/super.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/efivarfs/super.c b/fs/efivarfs/super.c
> index 5b68e4294faa..ca98c4e31eb7 100644
> --- a/fs/efivarfs/super.c
> +++ b/fs/efivarfs/super.c
> @@ -145,7 +145,7 @@ static int efivarfs_callback(efi_char16_t *name16, efi_guid_t vendor,
>   
>   	name[len + EFI_VARIABLE_GUID_LEN+1] = '\0';
>   
> -	inode = efivarfs_get_inode(sb, d_inode(root), S_IFREG | 0644, 0,
> +	inode = efivarfs_get_inode(sb, d_inode(root), S_IFREG | 0600, 0,
>   				   is_removable);
>   	if (!inode)
>   		goto fail_name;
> @@ -207,7 +207,7 @@ static int efivarfs_fill_super(struct super_block *sb, void *data, int silent)
>   	sb->s_d_op		= &efivarfs_d_ops;
>   	sb->s_time_gran         = 1;
>   
> -	inode = efivarfs_get_inode(sb, NULL, S_IFDIR | 0755, 0, true);
> +	inode = efivarfs_get_inode(sb, NULL, S_IFDIR | 0700, 0, true);
>   	if (!inode)
>   		return -ENOMEM;
>   	inode->i_op = &efivarfs_dir_inode_operations;
>