Messages in this thread Patch in this message |  | | From | Sasha Levin <> | Subject | [PATCH AUTOSEL 4.4 50/56] tty: pty: Fix race condition between release_one_tty and pty_write | Date | Sat, 1 Jun 2019 09:25:54 -0400 |
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From: Sahara <keun-o.park@darkmatter.ae>
[ Upstream commit b9ca5f8560af244489b4a1bc1ae88b341f24bc95 ]
Especially when a linked tty is used such as pty, the linked tty port's buf works have not been cancelled while master tty port's buf work has been cancelled. Since release_one_tty and flush_to_ldisc run in workqueue threads separately, when pty_cleanup happens and link tty port is freed, flush_to_ldisc tries to access freed port and port->itty, eventually it causes a panic. This patch utilizes the magic value with holding the tty_mutex to check if the tty->link is valid.
Fixes: 2b022ab7542d ("pty: cancel pty slave port buf's work in tty_release") Signed-off-by: Sahara <keun-o.park@darkmatter.ae> Cc: stable <stable@vger.kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Sasha Levin <sashal@kernel.org> --- drivers/tty/pty.c | 7 +++++++ drivers/tty/tty_io.c | 3 +++ 2 files changed, 10 insertions(+)
diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c index c8a2e5b0eff76..0e10600f3884d 100644 --- a/drivers/tty/pty.c +++ b/drivers/tty/pty.c @@ -111,6 +111,12 @@ static int pty_write(struct tty_struct *tty, const unsigned char *buf, int c) if (tty->stopped) return 0; + mutex_lock(&tty_mutex); + if (to->magic != TTY_MAGIC) { + mutex_unlock(&tty_mutex); + return -EIO; + } + if (c > 0) { spin_lock_irqsave(&to->port->lock, flags); /* Stuff the data into the input queue of the other end */ @@ -120,6 +126,7 @@ static int pty_write(struct tty_struct *tty, const unsigned char *buf, int c) tty_flip_buffer_push(to->port); spin_unlock_irqrestore(&to->port->lock, flags); } + mutex_unlock(&tty_mutex); return c; } diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c index b7effcfee91d8..acaf244859039 100644 --- a/drivers/tty/tty_io.c +++ b/drivers/tty/tty_io.c @@ -1639,10 +1639,13 @@ static void release_one_tty(struct work_struct *work) struct tty_driver *driver = tty->driver; struct module *owner = driver->owner; + mutex_lock(&tty_mutex); if (tty->ops->cleanup) tty->ops->cleanup(tty); tty->magic = 0; + mutex_unlock(&tty_mutex); + tty_driver_kref_put(driver); module_put(owner); -- 2.20.1
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