On Sun, Sep 23, 2012 at 05:19:06AM +0100, Al Viro wrote:
> On Sat, Sep 22, 2012 at 08:50:44PM -0700, Eric W. Biederman wrote:
>
> > +struct inode *devpts_redirect(struct file *filp)
> > +{
> > + struct inode *inode;
> > + struct file *filp2;
> > +
> > + /* Is the inode already a devpts inode? */
> > + inode = filp->f_dentry->d_inode;
> > + if (filp->f_dentry->d_sb->s_magic == DEVPTS_SUPER_MAGIC)
> > + goto out;
> > +
> > + /* Is f_dentry->d_parent usable? */
> > + inode = ERR_PTR(-ENODEV);
> > + if (filp->f_vfsmnt->mnt_root == filp->f_dentry)
> > + goto out;
> > +
> > + /* Is there a devpts inode we can use instead? */
> > +
> > + filp2 = file_open_root(filp->f_dentry->d_parent, filp->f_vfsmnt,
> > + "pts/ptmx", O_PATH);
> > + if (!IS_ERR(filp2)) {
> > + if (filp2->f_dentry->d_sb->s_magic == DEVPTS_SUPER_MAGIC) {
> > + struct path old;
> > + old = filp->f_path;
> > + filp->f_path = filp2->f_path;
> > + inode = filp->f_dentry->d_inode;
> > + path_get(&filp->f_path);
> > + path_put(&old);
>
> You are welcome to supply an analysis of the reasons why ->open() pulling
> such tricks will not break all kinds of code in VFS.
> > + }
> > + fput(filp2);
>
> ... starting with "what happens when some joker binds /dev/ptmx on
> /dev/pts/ptmx"
Or does mknod /tmp/ptmx c 5 2; mkdir /tmp/pts; ln /tmp/ptmx /tmp/pts/ptmx,
for that matter...
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