Re: [PATCH v2 3/3] ovl: check IS_APPEND() on real upper inode

[Miklos Szeredi <miklos@szeredi.hu>]

On Fri, Apr 7, 2017 at 11:01 AM, Amir Goldstein <amir73il@gmail.com> wrote:
> For overlay file open, check IS_APPEND() on the real upper inode
> inside d_real(), because the overlay inode does not have the
> S_APPEND flag and IS_APPEND() can only be checked at open time.
>
> Note that because overlayfs does not copy up the chattr inode flags
> (i.e. S_APPEND, S_IMMUTABLE), the IS_APPEND() check is only relevant
> for upper inodes that were set with chattr +a and not to lower
> inodes that had chattr +a before copy up.

Okay.   Maybe rename ovl_may_open() to ovl_check_append_only(),
because that what it does.

Thanks,
Miklos

>
> Signed-off-by: Amir Goldstein <amir73il@gmail.com>
> ---
>  fs/overlayfs/super.c | 30 +++++++++++++++++++++++++++---
>  1 file changed, 27 insertions(+), 3 deletions(-)
>
> diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> index c9e70d3..13806b8 100644
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -49,11 +49,30 @@ static void ovl_dentry_release(struct dentry *dentry)
>         }
>  }
>
> +static int ovl_may_open(struct dentry *dentry, int flag)
> +{
> +       struct inode *inode = dentry->d_inode;
> +
> +       /*
> +        * This test was moot in vfs may_open() because overlay inode does
> +        * not have the S_APPEND flag
> +        */
> +       if (IS_APPEND(inode)) {
> +               if  ((flag & O_ACCMODE) != O_RDONLY && !(flag & O_APPEND))
> +                       return -EPERM;
> +               if (flag & O_TRUNC)
> +                       return -EPERM;
> +       }
> +
> +       return 0;
> +}
> +
>  static struct dentry *ovl_d_real(struct dentry *dentry,
>                                  const struct inode *inode,
>                                  unsigned int open_flags)
>  {
>         struct dentry *real;
> +       int err;
>
>         if (!d_is_reg(dentry)) {
>                 if (!inode || inode == d_inode(dentry))
> @@ -65,15 +84,20 @@ static struct dentry *ovl_d_real(struct dentry *dentry,
>                 return dentry;
>
>         if (open_flags) {
> -               int err = ovl_open_maybe_copy_up(dentry, open_flags);
> -
> +               err = ovl_open_maybe_copy_up(dentry, open_flags);
>                 if (err)
>                         return ERR_PTR(err);
>         }
>
>         real = ovl_dentry_upper(dentry);
> -       if (real && (!inode || inode == d_inode(real)))
> +       if (real && (!inode || inode == d_inode(real))) {
> +               if (!inode) {
> +                       err = ovl_may_open(real, open_flags);
> +                       if (err)
> +                               return ERR_PTR(err);
> +               }
>                 return real;
> +       }
>
>         real = ovl_dentry_lower(dentry);
>         if (!real)
> --
> 2.7.4
>