This is a note to let you know that I've just added the patch titled
pty: fix possible use after free of tty->driver_data
to my tty git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git
in the tty-linus branch.
The patch will show up in the next release of the linux-next tree
(usually sometime within the next 24 hours during the week.)
The patch will hopefully also be merged in Linus's tree for the
next -rc kernel release.
If you have any questions about this process, please let me know.
>From 2831c89f42dcde440cfdccb9fee9f42d54bbc1ef Mon Sep 17 00:00:00 2001
From: "Herton R. Krzesinski" <herton@xxxxxxxxxx>
Date: Mon, 11 Jan 2016 12:07:43 -0200
Subject: pty: fix possible use after free of tty->driver_data
This change fixes a bug for a corner case where we have the the last
release from a pty master/slave coming from a previously opened /dev/tty
file. When this happens, the tty->driver_data can be stale, due to all
ptmx or pts/N files having already been closed before (and thus the inode
related to these files, which tty->driver_data points to, being already
freed/destroyed).
The fix here is to keep a reference on the opened master ptmx inode.
We maintain the inode referenced until the final pty_unix98_shutdown,
and only pass this inode to devpts_kill_index.
Signed-off-by: Herton R. Krzesinski <herton@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # 2.6.29+
Reviewed-by: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/tty/pty.c | 18 +++++++++++++++++-
1 file changed, 17 insertions(+), 1 deletion(-)
diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
index b3110040164a..3b5cde833ee5 100644
--- a/drivers/tty/pty.c
+++ b/drivers/tty/pty.c
@@ -681,7 +681,14 @@ static void pty_unix98_remove(struct tty_driver *driver, struct tty_struct *tty)
/* this is called once with whichever end is closed last */
static void pty_unix98_shutdown(struct tty_struct *tty)
{
- devpts_kill_index(tty->driver_data, tty->index);
+ struct inode *ptmx_inode;
+
+ if (tty->driver->subtype == PTY_TYPE_MASTER)
+ ptmx_inode = tty->driver_data;
+ else
+ ptmx_inode = tty->link->driver_data;
+ devpts_kill_index(ptmx_inode, tty->index);
+ iput(ptmx_inode); /* drop reference we acquired at ptmx_open */
}
static const struct tty_operations ptm_unix98_ops = {
@@ -773,6 +780,15 @@ static int ptmx_open(struct inode *inode, struct file *filp)
set_bit(TTY_PTY_LOCK, &tty->flags); /* LOCK THE SLAVE */
tty->driver_data = inode;
+ /*
+ * In the case where all references to ptmx inode are dropped and we
+ * still have /dev/tty opened pointing to the master/slave pair (ptmx
+ * is closed/released before /dev/tty), we must make sure that the inode
+ * is still valid when we call the final pty_unix98_shutdown, thus we
+ * hold an additional reference to the ptmx inode
+ */
+ ihold(inode);
+
tty_add_file(tty, filp);
slave_inode = devpts_pty_new(inode,
--
2.7.0
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