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| author | Herton R. Krzesinski <herton@redhat.com> | 2016-01-11 12:07:43 -0200 |
|---|---|---|
| committer | Sasha Levin <sasha.levin@oracle.com> | 2016-03-02 15:19:15 -0500 |
| commit | f8b4df5f7d7af74cf5270fbce89a089ecfe73604 (patch) | |
| tree | db6b51daf87b37e0ef2d3436bcce3693eb50eb45 | |
| parent | f46aa4a4ac73e4d0dcc90f757879477053774df2 (diff) | |
| download | lwn-f8b4df5f7d7af74cf5270fbce89a089ecfe73604.tar.gz lwn-f8b4df5f7d7af74cf5270fbce89a089ecfe73604.zip | |
pty: fix possible use after free of tty->driver_data
[ 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 <herton@redhat.com>
Cc: <stable@vger.kernel.org> # 2.6.29+
Reviewed-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
| -rw-r--r-- | drivers/tty/pty.c | 18 |
1 files changed, 17 insertions, 1 deletions
diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c index 082304dcbe8c..2c7e0ed35f12 100644 --- a/drivers/tty/pty.c +++ b/drivers/tty/pty.c @@ -655,7 +655,14 @@ 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 = { @@ -748,6 +755,15 @@ 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, |