Commit 8f9cfeed authored Mar 28, 2015 by Pan Xinhui Committed by Greg Kroah-Hartman May 10, 2015

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@intel.com>
Fixes: dfabf7ff
Cc: stable <stable@vger.kernel.org> # 3.14+
Acked-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent ec618478

drivers/tty/n_gsm.c

+2 −3

Original line number	Diff line number	Diff line
		@@ -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,
		};

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