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>

3 files changed, 6 insertions, 17 deletions

diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
index d8653ab6f498..03147fa31d47 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)) {
diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index e41b9bbc107d..fbcc14063804 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -1365,7 +1365,6 @@ static int tty_reopen(struct tty_struct *tty)
  *      @driver: tty driver we are opening a device on
  *      @idx: device index
  *      @ret_tty: returned tty structure
- *      @first_ok: ok to open a new device (used by ptmx)
  *
  *      Prepare a tty device. This may not be a "new" clean device but
  *      could also be an active device. The pty drivers require special
@@ -1385,18 +1384,11 @@ static int tty_reopen(struct tty_struct *tty)
  * relaxed for the (most common) case of reopening a tty.
  */
 
-struct tty_struct *tty_init_dev(struct tty_driver *driver, int idx,
-                                                                int first_ok)
+struct tty_struct *tty_init_dev(struct tty_driver *driver, int idx)
 {
         struct tty_struct *tty;
         int retval;
 
-        /* Check if pty master is being opened multiple times */
-        if (driver->subtype == PTY_TYPE_MASTER &&
-                (driver->flags & TTY_DRIVER_DEVPTS_MEM) && !first_ok) {
-                return ERR_PTR(-EIO);
-        }
-
         /*
          * First time open is complex, especially for PTY devices.
          * This code guarantees that either everything succeeds and the
@@ -1950,7 +1942,7 @@ retry_open:
                 if (retval)
                         tty = ERR_PTR(retval);
         } else
-                tty = tty_init_dev(driver, index, 0);
+                tty = tty_init_dev(driver, index);
 
         mutex_unlock(&tty_mutex);
         if (driver)
diff --git a/include/linux/tty.h b/include/linux/tty.h
index 5dbb3cb05a82..d3ebd765b548 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -480,8 +480,7 @@ extern void free_tty_struct(struct tty_struct *tty);
 extern void initialize_tty_struct(struct tty_struct *tty,
                 struct tty_driver *driver, int idx);
 extern void deinitialize_tty_struct(struct tty_struct *tty);
-extern struct tty_struct *tty_init_dev(struct tty_driver *driver, int idx,
-                                                                int first_ok);
+extern struct tty_struct *tty_init_dev(struct tty_driver *driver, int idx);
 extern int tty_release(struct inode *inode, struct file *filp);
 extern int tty_init_termios(struct tty_struct *tty);