On Fri, Jan 18, 2019 at 03:53:41PM +0100, Christian Brauner wrote:
> We don't allow to unlink it since it is crucial for binderfs to be useable
> but if we allow to rename it we make the unlink trivial to bypass. So
> prevent renaming too and simply treat the control dentry as immutable.
>
> Take the opportunity and turn the check for the control dentry into a
> separate helper is_binderfs_control_device() since it's now used in two
> places.
> Additionally, replace the custom rename dance we did with call to
> simple_rename().
Umm...
> +static inline bool is_binderfs_control_device(const struct inode *inode,
> + const struct dentry *dentry)
> +{
> + return BINDERFS_I(inode)->control_dentry == dentry;
> +}
What do you need an inode for?
static inline struct binderfs_info *BINDERFS_I(const struct inode *inode)
{
return inode->i_sb->s_fs_info;
}
so it looks like all you care about is the superblock. Which can be
had simply as dentry->d_sb...
Besides, what's the point of calling is_binderfs_device() in ->rename()?
If your directory methods are given dentries from another filesystem,
the kernel is already FUBAR. So your rename should simply do
if (is_binderfs_control_device(old_dentry) ||
is_binderfs_control_device(new_dentry))
return -EPERM;
return simple_rename(......);
and that's it...
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