[PATCH] tty/n_gsm.c: fix a memory leak when gsmtty is removed

[PATCH] tty/n_gsm.c: fix a memory leak when gsmtty is removed

[Pan Xinhui]

In gsmtty_remove, we will put dlci. when dlci's ref-count is zero,
tty_port_destructor will be called, and it will check if port->itty is NULL.
However port->itty will be set to NULL in release_tty after gsmtty_remove.
that may cause memory leak. so we use queue_work to put the dlci later.

Signed-off-by: xinhui.pan <xinhuix.pan@intel.com>
---
  drivers/tty/n_gsm.c | 16 ++++++++++++++--
  1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index c434376..50f4660 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -135,6 +135,7 @@ struct gsm_dlci {
  #define DLCI_OPEN		2	/* SABM/UA complete */
  #define DLCI_CLOSING		3	/* Sending DISC not seen UA/DM */
  	struct mutex mutex;
+	struct work_struct putself_work;
  
  	/* Link layer */
  	spinlock_t lock;	/* Protects the internal state */
@@ -3170,14 +3171,25 @@ static int gsmtty_break_ctl(struct tty_struct *tty, int state)
  	return gsmtty_modem_update(dlci, encode);
  }
  
-static void gsmtty_remove(struct tty_driver *driver, struct tty_struct *tty)
+static void put_gsm_dlci(struct work_struct *work)
  {
-	struct gsm_dlci *dlci = tty->driver_data;
+	struct gsm_dlci *dlci =
+		container_of(work, struct gsm_dlci, putself_work);
  	struct gsm_mux *gsm = dlci->gsm;
  
+	mutex_lock(&gsm->mutex);
  	dlci_put(dlci);
  	dlci_put(gsm->dlci[0]);
+	mutex_unlock(&gsm->mutex);
  	mux_put(gsm);
+}
+
+static void gsmtty_remove(struct tty_driver *driver, struct tty_struct *tty)
+{
+	struct gsm_dlci *dlci = tty->driver_data;
+
+	INIT_WORK(&dlci->putself_work, put_gsm_dlci);
+	schedule_work(&dlci->putself_work);
  	driver->ttys[tty->index] = NULL;
  }
  
-- 
1.9.1

[PATCH v2] tty/n_gsm.c: fix a memory leak when gsmtty is removed

[Pan Xinhui]

when gsmtty_remove put dlci, it will cause memory leak if
dlci->port's refcount is zero.
So we do the cleanup work in .cleanup callback instead.

dlci will be last put in two call chains.
1) gsmld_close -> gsm_cleanup_mux -> gsm_dlci_release -> dlci_put
2) gsmld_remove -> dlci_put
so there is a race. the memory leak depends on the race.

In call chain 2. we hit the memory leak. bellow comment tells.

release_tty -> tty_driver_remove_tty -> gsmtty_remove -> dlci_put -> tty_port_destructor (WARN_ON(port->itty) and return directly)
						|
						--> tty->port->itty = NULL;
			|
		tty_kref_put ---> release_one_tty -> gsmtty_cleanup (now we do the cleanup work here.)
So our patch fix it by doing the cleanup work after tty core did.

Signed-off-by: xinhui.pan <xinhuix.pan@intel.com>
---
  drivers/tty/n_gsm.c | 5 ++---
  1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index c434376..bce16e4 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -3170,7 +3170,7 @@ static int gsmtty_break_ctl(struct tty_struct *tty, int state)
  	return gsmtty_modem_update(dlci, encode);
  }
  
-static void gsmtty_remove(struct tty_driver *driver, struct tty_struct *tty)
+static void gsmtty_cleanup(struct tty_struct *tty)
  {
  	struct gsm_dlci *dlci = tty->driver_data;
  	struct gsm_mux *gsm = dlci->gsm;
@@ -3178,7 +3178,6 @@ static void gsmtty_remove(struct tty_driver *driver, struct tty_struct *tty)
  	dlci_put(dlci);
  	dlci_put(gsm->dlci[0]);
  	mux_put(gsm);
-	driver->ttys[tty->index] = NULL;
  }
  
  /* Virtual ttys for the demux */
@@ -3199,7 +3198,7 @@ static const struct tty_operations gsmtty_ops = {
  	.tiocmget		= gsmtty_tiocmget,
  	.tiocmset		= gsmtty_tiocmset,
  	.break_ctl		= gsmtty_break_ctl,
-	.remove			= gsmtty_remove,
+	.cleanup		= gsmtty_cleanup,
  };
  
  
-- 
1.9.1

Re: [PATCH v2] tty/n_gsm.c: fix a memory leak when gsmtty is removed

[Greg KH]

On Wed, Mar 25, 2015 at 03:05:33PM +0800, Pan Xinhui wrote:
> when gsmtty_remove put dlci, it will cause memory leak if
> dlci->port's refcount is zero.
> So we do the cleanup work in .cleanup callback instead.
> 
> dlci will be last put in two call chains.
> 1) gsmld_close -> gsm_cleanup_mux -> gsm_dlci_release -> dlci_put
> 2) gsmld_remove -> dlci_put
> so there is a race. the memory leak depends on the race.
> 
> In call chain 2. we hit the memory leak. bellow comment tells.
> 
> release_tty -> tty_driver_remove_tty -> gsmtty_remove -> dlci_put -> tty_port_destructor (WARN_ON(port->itty) and return directly)
> 						|
> 						--> tty->port->itty = NULL;
> 			|
> 		tty_kref_put ---> release_one_tty -> gsmtty_cleanup (now we do the cleanup work here.)

That doesn't line up at all :(

> So our patch fix it by doing the cleanup work after tty core did.
> 
> Signed-off-by: xinhui.pan <xinhuix.pan@intel.com>

I need a real name here, "xinhui.pan" is not your real name, according
to your "From:" line, right?

Please fix up and resend.

And also include what changed from the previous version, this is much
different.

thanks,

greg k-h

[PATCH v2 RESEND] tty/n_gsm.c: fix a memory leak when gsmtty is removed

[Pan Xinhui]

when gsmtty_remove put dlci, it will cause memory leak if dlci->port's refcount is zero.
So we do the cleanup work in .cleanup callback instead.

dlci will be last put in two call chains.
1) gsmld_close -> gsm_cleanup_mux -> gsm_dlci_release -> dlci_put
2) gsmld_remove -> dlci_put
so there is a race. the memory leak depends on the race.

In call chain 2. we hit the memory leak. below comment tells.

release_tty -> tty_driver_remove_tty -> gsmtty_remove -> dlci_put -> tty_port_destructor (WARN_ON(port->itty) and return directly)
                         |
                tty->port->itty = NULL;
                         |
                tty_kref_put ---> release_one_tty -> gsmtty_cleanup (added by our patch)

So our patch fix the memory leak by doing the cleanup work after tty core did.

Signed-off-by: Pan Xinhui <xinhuix.pan@intel.com>
---
Changes in v2:
  Don't use schedule_work to put dlci. Replace .remove with .cleanup callback.

  drivers/tty/n_gsm.c | 5 ++---
  1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index c434376..bce16e4 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -3170,7 +3170,7 @@ static int gsmtty_break_ctl(struct tty_struct *tty, int state)
  	return gsmtty_modem_update(dlci, encode);
  }
  
-static void gsmtty_remove(struct tty_driver *driver, struct tty_struct *tty)
+static void gsmtty_cleanup(struct tty_struct *tty)
  {
  	struct gsm_dlci *dlci = tty->driver_data;
  	struct gsm_mux *gsm = dlci->gsm;
@@ -3178,7 +3178,6 @@ static void gsmtty_remove(struct tty_driver *driver, struct tty_struct *tty)
  	dlci_put(dlci);
  	dlci_put(gsm->dlci[0]);
  	mux_put(gsm);
-	driver->ttys[tty->index] = NULL;
  }
  
  /* Virtual ttys for the demux */
@@ -3199,7 +3198,7 @@ static const struct tty_operations gsmtty_ops = {
  	.tiocmget		= gsmtty_tiocmget,
  	.tiocmset		= gsmtty_tiocmset,
  	.break_ctl		= gsmtty_break_ctl,
-	.remove			= gsmtty_remove,
+	.cleanup		= gsmtty_cleanup,
  };
  
  
-- 
1.9.1

Re: [PATCH v2 RESEND] tty/n_gsm.c: fix a memory leak when gsmtty is removed

[Jiri Slaby]

On 03/28/2015, 03:42 AM, Pan Xinhui wrote:
> when gsmtty_remove put dlci, it will cause memory leak if dlci->port's
> refcount is zero.
> So we do the cleanup work in .cleanup callback instead.
> 
> dlci will be last put in two call chains.
> 1) gsmld_close -> gsm_cleanup_mux -> gsm_dlci_release -> dlci_put
> 2) gsmld_remove -> dlci_put
> so there is a race. the memory leak depends on the race.
> 
> In call chain 2. we hit the memory leak. below comment tells.
> 
> release_tty -> tty_driver_remove_tty -> gsmtty_remove -> dlci_put ->
> tty_port_destructor (WARN_ON(port->itty) and return directly)
>                         |
>                tty->port->itty = NULL;
>                         |
>                tty_kref_put ---> release_one_tty -> gsmtty_cleanup
> (added by our patch)
> 
> So our patch fix the memory leak by doing the cleanup work after tty
> core did.
> 
> Signed-off-by: Pan Xinhui <xinhuix.pan@intel.com>

Fixes: dfabf7ffa30585
Acked-by: Jiri Slaby <jslaby@suse.cz>

> ---
> Changes in v2:
>  Don't use schedule_work to put dlci. Replace .remove with .cleanup
> callback.
> 
>  drivers/tty/n_gsm.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
> index c434376..bce16e4 100644
> --- a/drivers/tty/n_gsm.c
> +++ b/drivers/tty/n_gsm.c
> @@ -3170,7 +3170,7 @@ static int gsmtty_break_ctl(struct tty_struct
> *tty, int state)
>      return gsmtty_modem_update(dlci, encode);
>  }
>  
> -static void gsmtty_remove(struct tty_driver *driver, struct tty_struct
> *tty)
> +static void gsmtty_cleanup(struct tty_struct *tty)
>  {
>      struct gsm_dlci *dlci = tty->driver_data;
>      struct gsm_mux *gsm = dlci->gsm;
> @@ -3178,7 +3178,6 @@ static void gsmtty_remove(struct tty_driver
> *driver, struct tty_struct *tty)
>      dlci_put(dlci);
>      dlci_put(gsm->dlci[0]);
>      mux_put(gsm);
> -    driver->ttys[tty->index] = NULL;
>  }
>  
>  /* Virtual ttys for the demux */
> @@ -3199,7 +3198,7 @@ static const struct tty_operations gsmtty_ops = {
>      .tiocmget        = gsmtty_tiocmget,
>      .tiocmset        = gsmtty_tiocmset,
>      .break_ctl        = gsmtty_break_ctl,
> -    .remove            = gsmtty_remove,
> +    .cleanup        = gsmtty_cleanup,
>  };
>  
>  


-- 
js
suse labs