+ tty->session == NULL) {
+ /*
+ * Don't let a process that only has write access to the tty
+ * obtain the privileges associated with having a tty as
+ * controlling terminal (being able to reopen it with full
+ * access through /dev/tty, being able to perform pushback).
+ * Many distributions set the group of all ttys to "tty" and
+ * grant write-only access to all terminals for setgid tty
+ * binaries, which should not imply full privileges on all ttys.
+ *
+ * This could theoretically break old code that performs open()
+ * on a write-only file descriptor. In that case, it might be
+ * necessary to also permit this if
+ * inode_permission(inode, MAY_READ) == 0.
+ */
+ if (filp->f_mode & FMODE_READ)
+ __proc_set_tty(tty);
+ }