svn commit: r200732 - in head/sys: fs/devfs kern sys

[Kostik Belousov]

On Sat, Dec 19, 2009 at 06:42:12PM +0000, Ed Schouten wrote:
> Author: ed
> Date: Sat Dec 19 18:42:12 2009
> New Revision: 200732
> URL: http://svn.freebsd.org/changeset/base/200732
> 
> Log:
>   Let access overriding to TTYs depend on the cdev_priv, not the vnode.
>   
>   Basically this commit changes two things, which improves access to TTYs
>   in exceptional conditions. Basically the problem was that when you ran
>   jexec(8) to attach to a jail, you couldn't use /dev/tty (well, also the
>   node of the actual TTY, e.g. /dev/pts/X). This is very inconvenient if
>   you want to attach to screens quickly, use ssh(1), etc.
>   
>   The fixes:
>   
>   - Cache the cdev_priv of the controlling TTY in struct session. Change
>     devfs_access() to compare against the cdev_priv instead of the vnode.
>     This allows you to bypass UNIX permissions, even across different
>     mounts of devfs.
>   
>   - Extend devfs_prison_check() to unconditionally expose the device node
>     of the controlling TTY, even if normal prison nesting rules normally
>     don't allow this. This actually allows you to interact with this
>     device node.
>   
>   To be honest, I'm not really happy with this solution. We now have to
>   store three pointers to a controlling TTY (s_ttyp, s_ttyvp, s_ttydp).
>   In an ideal world, we should just get rid of the latter two and only use
>   s_ttyp, but this makes certian pieces of code very impractical (e.g.
>   devfs, kern_exit.c).

Note that struct devfs_dirent is available as vp->v_data, and
devfs_dirent' de_cdp member contains pointer to cdev_priv. I think this
would allow to remove s_ttydp.
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