TTY: move debug checking out of tty_release

There is no need to taint the tty_release code with paranoia
checking. So move it out of line to a separate function. Making thus
tty_release more readable.

[v2] don't introduce a hard to reproduce use after free (scheduled work would
     need to preempt the current thread)

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 57 insertions, 44 deletions

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 76e66ff5e65d..b874b6d1b0be 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -1557,6 +1557,62 @@ static void release_tty(struct tty_struct *tty, int idx)
 }
 
 /**
+ *      tty_release_checks - check a tty before real release
+ *      @tty: tty to check
+ *      @o_tty: link of @tty (if any)
+ *      @idx: index of the tty
+ *
+ *      Performs some paranoid checking before true release of the @tty.
+ *      This is a no-op unless TTY_PARANOIA_CHECK is defined.
+ */
+static int tty_release_checks(struct tty_struct *tty, struct tty_struct *o_tty,
+                int idx)
+{
+#ifdef TTY_PARANOIA_CHECK
+        if (idx < 0 || idx >= tty->driver->num) {
+                printk(KERN_DEBUG "tty_release_dev: bad idx when trying to "
+                                  "free (%s)\n", tty->name);
+                return -1;
+        }
+
+        /* not much to check for devpts */
+        if (tty->driver->flags & TTY_DRIVER_DEVPTS_MEM)
+                return 0;
+
+        if (tty != tty->driver->ttys[idx]) {
+                printk(KERN_DEBUG "tty_release_dev: driver.table[%d] not tty "
+                       "for (%s)\n", idx, tty->name);
+                return -1;
+        }
+        if (tty->termios != tty->driver->termios[idx]) {
+                printk(KERN_DEBUG "tty_release_dev: driver.termios[%d] not termios "
+                       "for (%s)\n",
+                       idx, tty->name);
+                return -1;
+        }
+        if (tty->driver->other) {
+                if (o_tty != tty->driver->other->ttys[idx]) {
+                        printk(KERN_DEBUG "tty_release_dev: other->table[%d] "
+                                          "not o_tty for (%s)\n",
+                               idx, tty->name);
+                        return -1;
+                }
+                if (o_tty->termios != tty->driver->other->termios[idx]) {
+                        printk(KERN_DEBUG "tty_release_dev: other->termios[%d] "
+                                          "not o_termios for (%s)\n",
+                               idx, tty->name);
+                        return -1;
+                }
+                if (o_tty->link != tty) {
+                        printk(KERN_DEBUG "tty_release_dev: bad pty pointers\n");
+                        return -1;
+                }
+        }
+#endif
+        return 0;
+}
+
+/**
  *      tty_release             -       vfs callback for close
  *      @inode: inode of tty
  *      @filp: file pointer for handle to tty
@@ -1598,59 +1654,16 @@ int tty_release(struct inode *inode, struct file *filp)
         devpts = (tty->driver->flags & TTY_DRIVER_DEVPTS_MEM) != 0;
         o_tty = tty->link;
 
-#ifdef TTY_PARANOIA_CHECK
-        if (idx < 0 || idx >= tty->driver->num) {
-                printk(KERN_DEBUG "tty_release_dev: bad idx when trying to "
-                                  "free (%s)\n", tty->name);
+        if (tty_release_checks(tty, o_tty, idx)) {
                 tty_unlock();
                 return 0;
         }
-        if (!devpts) {
-                if (tty != tty->driver->ttys[idx]) {
-                        tty_unlock();
-                        printk(KERN_DEBUG "tty_release_dev: driver.table[%d] not tty "
-                               "for (%s)\n", idx, tty->name);
-                        return 0;
-                }
-                if (tty->termios != tty->driver->termios[idx]) {
-                        tty_unlock();
-                        printk(KERN_DEBUG "tty_release_dev: driver.termios[%d] not termios "
-                               "for (%s)\n",
-                               idx, tty->name);
-                        return 0;
-                }
-        }
-#endif
 
 #ifdef TTY_DEBUG_HANGUP
         printk(KERN_DEBUG "tty_release_dev of %s (tty count=%d)...",
                tty_name(tty, buf), tty->count);
 #endif
 
-#ifdef TTY_PARANOIA_CHECK
-        if (tty->driver->other &&
-             !(tty->driver->flags & TTY_DRIVER_DEVPTS_MEM)) {
-                if (o_tty != tty->driver->other->ttys[idx]) {
-                        tty_unlock();
-                        printk(KERN_DEBUG "tty_release_dev: other->table[%d] "
-                                          "not o_tty for (%s)\n",
-                               idx, tty->name);
-                        return 0 ;
-                }
-                if (o_tty->termios != tty->driver->other->termios[idx]) {
-                        tty_unlock();
-                        printk(KERN_DEBUG "tty_release_dev: other->termios[%d] "
-                                          "not o_termios for (%s)\n",
-                               idx, tty->name);
-                        return 0;
-                }
-                if (o_tty->link != tty) {
-                        tty_unlock();
-                        printk(KERN_DEBUG "tty_release_dev: bad pty pointers\n");
-                        return 0;
-                }
-        }
-#endif
         if (tty->ops->close)
                 tty->ops->close(tty, filp);