linux-kernel - Re: [PATCH 8/9] overlayfs: Dilute permission checks on lower only if not special file

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Message-ID: <CAJfpegsTUcDOwE6Y_2A+erSWrK+6prFe8ztj8zm0X=Nyro+Y=g@mail.gmail.com>
Date:	Thu, 14 Jul 2016 08:51:48 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	Stephen Smalley <sds@...ho.nsa.gov>, pmoore@...hat.com,
	Casey Schaufler <casey@...aufler-ca.com>,
	linux-kernel@...r.kernel.org,
	"linux-unionfs@...r.kernel.org" <linux-unionfs@...r.kernel.org>,
	LSM <linux-security-module@...r.kernel.org>,
	Daniel J Walsh <dwalsh@...hat.com>,
	David Howells <dhowells@...hat.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 8/9] overlayfs: Dilute permission checks on lower only if
 not special file

On Wed, Jul 13, 2016 at 4:44 PM, Vivek Goyal <vgoyal@...hat.com> wrote:
> Right now if file is on lower/, we remove MAY_WRITE/MAY_APPEND bits from
> mask as lower/ will never be written and file will be copied up. But this
> is not true for special files. These files are not copied up and are
> opened in place. So don't dilute the checks for these types of files.

Pushed this one as well.

Miklos

>
> Reported-by: Dan Walsh <dwalsh@...hat.com>
> Signed-off-by: Vivek Goyal <vgoyal@...hat.com>
> ---
>  fs/overlayfs/inode.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
> index 66f42f5..6d9d86e 100644
> --- a/fs/overlayfs/inode.c
> +++ b/fs/overlayfs/inode.c
> @@ -140,7 +140,7 @@ int ovl_permission(struct inode *inode, int mask)
>                 return err;
>
>         old_cred = ovl_override_creds(inode->i_sb);
> -       if (!is_upper)
> +       if (!is_upper && !special_file(realinode->i_mode))
>                 mask &= ~(MAY_WRITE | MAY_APPEND);
>         err = inode_permission(realinode, mask);
>         revert_creds(old_cred);
> --
> 2.7.4
>