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    SubjectRe: [PATCH 1/2] fs/efivarfs: restrict inode permissions
    On Tue, Feb 20, 2018 at 7:18 PM, Andy Lutomirski <luto@kernel.org> wrote:
    > 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.

    Alternatively, a patch like this (untested but straightforward) might
    be a little more effective and easier to undo in userspace for anyone
    who may be adversely affected:

    diff --git a/fs/efivarfs/super.c b/fs/efivarfs/super.c
    index 5b68e4294faa..88c7163c0ac1 100644
    --- a/fs/efivarfs/super.c
    +++ b/fs/efivarfs/super.c
    @@ -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;
    If you prefer that, I'd be happy to re-send it for real.

    --Andy

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