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authorPeter Hurley <peter@hurleysoftware.com>2016-01-10 22:40:55 -0800
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2016-01-26 23:17:54 -0800
commit5c17c861a357e9458001f021a7afa7aab9937439 (patch)
tree705a69af5bc3fddb08476928885297f895c4f501
parent7f22f6c935cda600660e623a411fe380015d28d9 (diff)
tty: Fix unsafe ldisc reference via ioctl(TIOCGETD)
ioctl(TIOCGETD) retrieves the line discipline id directly from the ldisc because the line discipline id (c_line) in termios is untrustworthy; userspace may have set termios via ioctl(TCSETS*) without actually changing the line discipline via ioctl(TIOCSETD). However, directly accessing the current ldisc via tty->ldisc is unsafe; the ldisc ptr dereferenced may be stale if the line discipline is changing via ioctl(TIOCSETD) or hangup. Wait for the line discipline reference (just like read() or write()) to retrieve the "current" line discipline id. Cc: <stable@vger.kernel.org> Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--drivers/tty/tty_io.c24
1 files changed, 23 insertions, 1 deletions
diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index a1b36bf..5cec01c 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -2659,6 +2659,28 @@ static int tiocsetd(struct tty_struct *tty, int __user *p)
}
/**
+ * tiocgetd - get line discipline
+ * @tty: tty device
+ * @p: pointer to user data
+ *
+ * Retrieves the line discipline id directly from the ldisc.
+ *
+ * Locking: waits for ldisc reference (in case the line discipline
+ * is changing or the tty is being hungup)
+ */
+
+static int tiocgetd(struct tty_struct *tty, int __user *p)
+{
+ struct tty_ldisc *ld;
+ int ret;
+
+ ld = tty_ldisc_ref_wait(tty);
+ ret = put_user(ld->ops->num, p);
+ tty_ldisc_deref(ld);
+ return ret;
+}
+
+/**
* send_break - performed time break
* @tty: device to break on
* @duration: timeout in mS
@@ -2884,7 +2906,7 @@ long tty_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
case TIOCGSID:
return tiocgsid(tty, real_tty, p);
case TIOCGETD:
- return put_user(tty->ldisc->ops->num, (int __user *)p);
+ return tiocgetd(tty, p);
case TIOCSETD:
return tiocsetd(tty, p);
case TIOCVHANGUP: