This is a note to let you know that I've just added the patch titled
tty: rpmsg: Fix race condition releasing tty port
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 db7f19c0aa0abcb751ff0ed694a071363f702b1d Mon Sep 17 00:00:00 2001 From: Arnaud Pouliquen arnaud.pouliquen@foss.st.com Date: Tue, 4 Jan 2022 17:35:45 +0100 Subject: tty: rpmsg: Fix race condition releasing tty port
The tty_port struct is part of the rpmsg_tty_port structure. The issue is that the rpmsg_tty_port structure is freed on rpmsg_tty_remove while it is still referenced in the tty_struct. Its release is not predictable due to workqueues.
For instance following ftrace shows that rpmsg_tty_close is called after rpmsg_tty_release_cport:
nr_test.sh-389 [000] ..... 212.093752: rpmsg_tty_remove <-rpmsg_dev_ remove cat-1191 [001] ..... 212.095697: tty_release <-__fput nr_test.sh-389 [000] ..... 212.099166: rpmsg_tty_release_cport <-rpm sg_tty_remove cat-1191 [001] ..... 212.115352: rpmsg_tty_close <-tty_release cat-1191 [001] ..... 212.115371: release_tty <-tty_release_str
As consequence, the port must be free only when user has released the TTY interface.
This path : - Introduce the .destruct port tty ops function to release the allocated rpmsg_tty_port structure. - Introduce the .hangup tty ops function to call tty_port_hangup. - Manages the tty port refcounting to trig the .destruct port ops, - Introduces the rpmsg_tty_cleanup function to ensure that the TTY is removed before decreasing the port refcount.
Fixes: 7c0408d80579 ("tty: add rpmsg driver") Cc: stable stable@vger.kernel.org Signed-off-by: Arnaud Pouliquen arnaud.pouliquen@foss.st.com Link: https://lore.kernel.org/r/20220104163545.34710-1-arnaud.pouliquen@foss.st.co... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/tty/rpmsg_tty.c | 40 ++++++++++++++++++++++++++-------------- 1 file changed, 26 insertions(+), 14 deletions(-)
diff --git a/drivers/tty/rpmsg_tty.c b/drivers/tty/rpmsg_tty.c index dae2a4e44f38..29db413bbc03 100644 --- a/drivers/tty/rpmsg_tty.c +++ b/drivers/tty/rpmsg_tty.c @@ -50,10 +50,17 @@ static int rpmsg_tty_cb(struct rpmsg_device *rpdev, void *data, int len, void *p static int rpmsg_tty_install(struct tty_driver *driver, struct tty_struct *tty) { struct rpmsg_tty_port *cport = idr_find(&tty_idr, tty->index); + struct tty_port *port;
tty->driver_data = cport;
- return tty_port_install(&cport->port, driver, tty); + port = tty_port_get(&cport->port); + return tty_port_install(port, driver, tty); +} + +static void rpmsg_tty_cleanup(struct tty_struct *tty) +{ + tty_port_put(tty->port); }
static int rpmsg_tty_open(struct tty_struct *tty, struct file *filp) @@ -106,12 +113,19 @@ static unsigned int rpmsg_tty_write_room(struct tty_struct *tty) return size; }
+static void rpmsg_tty_hangup(struct tty_struct *tty) +{ + tty_port_hangup(tty->port); +} + static const struct tty_operations rpmsg_tty_ops = { .install = rpmsg_tty_install, .open = rpmsg_tty_open, .close = rpmsg_tty_close, .write = rpmsg_tty_write, .write_room = rpmsg_tty_write_room, + .hangup = rpmsg_tty_hangup, + .cleanup = rpmsg_tty_cleanup, };
static struct rpmsg_tty_port *rpmsg_tty_alloc_cport(void) @@ -137,8 +151,10 @@ static struct rpmsg_tty_port *rpmsg_tty_alloc_cport(void) return cport; }
-static void rpmsg_tty_release_cport(struct rpmsg_tty_port *cport) +static void rpmsg_tty_destruct_port(struct tty_port *port) { + struct rpmsg_tty_port *cport = container_of(port, struct rpmsg_tty_port, port); + mutex_lock(&idr_lock); idr_remove(&tty_idr, cport->id); mutex_unlock(&idr_lock); @@ -146,7 +162,10 @@ static void rpmsg_tty_release_cport(struct rpmsg_tty_port *cport) kfree(cport); }
-static const struct tty_port_operations rpmsg_tty_port_ops = { }; +static const struct tty_port_operations rpmsg_tty_port_ops = { + .destruct = rpmsg_tty_destruct_port, +}; +
static int rpmsg_tty_probe(struct rpmsg_device *rpdev) { @@ -166,7 +185,8 @@ static int rpmsg_tty_probe(struct rpmsg_device *rpdev) cport->id, dev); if (IS_ERR(tty_dev)) { ret = dev_err_probe(dev, PTR_ERR(tty_dev), "Failed to register tty port\n"); - goto err_destroy; + tty_port_put(&cport->port); + return ret; }
cport->rpdev = rpdev; @@ -177,12 +197,6 @@ static int rpmsg_tty_probe(struct rpmsg_device *rpdev) rpdev->src, rpdev->dst, cport->id);
return 0; - -err_destroy: - tty_port_destroy(&cport->port); - rpmsg_tty_release_cport(cport); - - return ret; }
static void rpmsg_tty_remove(struct rpmsg_device *rpdev) @@ -192,13 +206,11 @@ static void rpmsg_tty_remove(struct rpmsg_device *rpdev) dev_dbg(&rpdev->dev, "Removing rpmsg tty device %d\n", cport->id);
/* User hang up to release the tty */ - if (tty_port_initialized(&cport->port)) - tty_port_tty_hangup(&cport->port, false); + tty_port_tty_hangup(&cport->port, false);
tty_unregister_device(rpmsg_tty_driver, cport->id);
- tty_port_destroy(&cport->port); - rpmsg_tty_release_cport(cport); + tty_port_put(&cport->port); }
static struct rpmsg_device_id rpmsg_driver_tty_id_table[] = {