From: Herton R. Krzesinski Date: Mon, 11 Jan 2016 14:07:43 +0000 (-0200) Subject: pty: fix possible use after free of tty->driver_data X-Git-Tag: v4.1.12-92~150^2~216 X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=87ec623ace85aec4babb2f42238a8795290e3d1b;p=users%2Fjedix%2Flinux-maple.git pty: fix possible use after free of tty->driver_data Orabug: 23330843 [ Upstream commit 2831c89f42dcde440cfdccb9fee9f42d54bbc1ef ] 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 Cc: # 2.6.29+ Reviewed-by: Peter Hurley Signed-off-by: Greg Kroah-Hartman Signed-off-by: Sasha Levin (cherry picked from commit 614f8734d11ad22ee17a5faecf355b70756904ef) Signed-off-by: Dan Duval --- diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c index 4d5e8409769c3..5c260c872af26 100644 --- a/drivers/tty/pty.c +++ b/drivers/tty/pty.c @@ -672,7 +672,14 @@ 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 = { @@ -764,6 +771,15 @@ 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,