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

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Date:	Sat, 28 Mar 2015 10:42:56 +0800
From:	Pan Xinhui <xinhuix.pan@...el.com>
To:	gregkh@...uxfoundation.org, jslaby@...e.cz,
	linux-kernel@...r.kernel.org
CC:	yanmin_zhang@...ux.intel.com, mnipxh@...il.com
Subject: [PATCH v2 RESEND] tty/n_gsm.c: fix a memory leak when gsmtty is removed

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@...el.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
--
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