On Fri, Apr 7, 2017 at 11:01 AM, Amir Goldstein <amir73il@xxxxxxxxx> 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@xxxxxxxxx>
> ---
> 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
>
