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From: Poul-Henning Kamp <phk@FreeBSD.org>
Date: Mon, 13 Jan 2003 14:20:37 -0800 (PST)
To: cvs-committers@FreeBSD.org, cvs-all@FreeBSD.org
Subject: cvs commit: src/sys/fs/devfs devfs_vnops.c
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phk         2003/01/13 14:20:37 PST

  Modified files:
    sys/fs/devfs         devfs_vnops.c 
  Log:
  Even if the permissions deny it, a process should be allowed to
  access its controlling terminal.
  
  In essense, history dictates that any process is allowed to open
  /dev/tty for RW, irrespective of credential, because by definition
  it is it's own controlling terminal.
  
  Before DEVFS we relied on a hacky half-device thing (kern/tty_tty.c)
  which did the magic deep down at device level, which at best was
  disgusting from an architectural point of view.
  
  My first shot at this was to use the cloning mechanism to simply
  give people the right tty when they ask for /dev/tty, that's why
  you get this, slightly counter intuitive result:
  
          syv# ls -l /dev/tty `tty`
          crw--w----  1 u1  tty    5,   0 Jan 13 22:14 /dev/tty
          crw--w----  1 u1  tty    5,   0 Jan 13 22:14 /dev/ttyp0
  
  Trouble is, when user u1 su(1)'s to user u2, he cannot open
  /dev/ttyp0 anymore because he doesn't have permission to do so.
  
  The above fix allows him to do that.
  
  The interesting side effect is that one was previously only able
  to access the controlling tty by indirection:
          date > /dev/tty
  but not by name:
          date > `tty`
  
  This is now possible, and that feels a lot more like DTRT.
  
  PR:             46635
  MFC candidate:  could be.
  
  Revision  Changes    Path
  1.58      +13 -2     src/sys/fs/devfs/devfs_vnops.c

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