tty: cleanup prohibition of direct opening for unix98 pty master

cleanup hack added in v2.6.27-3203-g15582d3

comment from that patch:

: pty: If the administrator creates a device for a ptmx slave we should not error
:
: The open path for ptmx slaves is via the ptmx device. Opening them any
: other way is not allowed. Vegard Nossum found that previously this was not
: the case and mknod foo c 128 42; cat foo would produce nasty diagnostics
:
: Signed-off-by: Alan Cox <alan@redhat.com>
: Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

devpts_get_tty() returns non-null only for inodes on devpts, but there is no
inodes for master-devices, /dev/ptmx (/dev/pts/ptmx) is the only way to open them.
Thus we can completely forbid lookup for master-devices and eliminate that hack in
tty_init_dev() because tty_open() will get EIO from tty_driver_lookup_tty().

Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 3 insertions, 5 deletions

diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
index d8653ab6f49..03147fa31d4 100644
--- a/drivers/tty/pty.c
+++ b/drivers/tty/pty.c
@@ -515,10 +515,8 @@ static int pty_unix98_ioctl(struct tty_struct *tty,
 static struct tty_struct *ptm_unix98_lookup(struct tty_driver *driver,
                 struct inode *ptm_inode, int idx)
 {
-        struct tty_struct *tty = devpts_get_tty(ptm_inode, idx);
-        if (tty)
-                tty = tty->link;
-        return tty;
+        /* Master must be open via /dev/ptmx */
+        return ERR_PTR(-EIO);
 }
 
 /**
@@ -677,7 +675,7 @@ static int ptmx_open(struct inode *inode, struct file *filp)
 
         mutex_lock(&tty_mutex);
         tty_lock();
-        tty = tty_init_dev(ptm_driver, index, 1);
+        tty = tty_init_dev(ptm_driver, index);
         mutex_unlock(&tty_mutex);
 
         if (IS_ERR(tty)) {