Re: [PATCH] ALSA: control led: fix memory leak in snd_ctl_led_register
From: Dan Carpenter
Date: Mon May 31 2021 - 07:02:54 EST
On Fri, May 28, 2021 at 09:17:57PM +0800, Dongliang Mu wrote:
> The snd_ctl_led_sysfs_add and snd_ctl_led_sysfs_remove should contain
> the refcount operations in pair. However, snd_ctl_led_sysfs_remove fails
> to decrease the refcount to zero, which causes device_release never to
> be invoked. This leads to memory leak to some resources, like struct
> device_private.
>
> Fix this by calling put_device at the end of snd_ctl_led_sysfs_remove
>
> Reported-by: syzbot+08a7d8b51ea048a74ffb@xxxxxxxxxxxxxxxxxxxxxxxxx
> Fixes: a135dfb5de1 ("ALSA: led control - add sysfs kcontrol LED marking layer")
> Signed-off-by: Dongliang Mu <mudongliangabcd@xxxxxxxxx>
> ---
> sound/core/control_led.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/sound/core/control_led.c b/sound/core/control_led.c
> index 25f57c14f294..fff2688b5019 100644
> --- a/sound/core/control_led.c
> +++ b/sound/core/control_led.c
> @@ -371,6 +371,10 @@ static void snd_ctl_led_disconnect(struct snd_card *card)
> snd_ctl_led_refresh();
> }
>
> +static void snd_ctl_led_release(struct device *dev)
> +{
> +}
Just to clarify again some more, this call back has to free "led_card".
This patch changes the memory leak into a use after free bug. (A use
after free bug is worse than a memory leak).
There were some other leaks as discussed where a dummy free function is
fine because they were dealing with static data structures (not
allocated memory).
> +
> /*
> * sysfs
> */
> @@ -663,6 +667,7 @@ static void snd_ctl_led_sysfs_add(struct snd_card *card)
> led_card->number = card->number;
> led_card->led = led;
> device_initialize(&led_card->dev);
> + led_card->dev.release = snd_ctl_led_release;
> if (dev_set_name(&led_card->dev, "card%d", card->number) < 0)
> goto cerr;
> led_card->dev.parent = &led->dev;
> @@ -701,6 +706,7 @@ static void snd_ctl_led_sysfs_remove(struct snd_card *card)
> sysfs_remove_link(&card->ctl_dev.kobj, link_name);
> sysfs_remove_link(&led_card->dev.kobj, "card");
> device_del(&led_card->dev);
> + put_device(&led_card->dev);
> kfree(led_card);
> led->cards[card->number] = NULL;
> }
Btw, I have created a Smatch warning for this type of code where we
have:
put_device(&foo->dev);
kfree(foo);
sound/core/control_led.c:709 snd_ctl_led_sysfs_remove() warn: freeing device managed memory: 'led_card'
So hopefully that will prevent future similar bugs. I'll test it out
overnight and report back tomorrow how it works.
regards,
dan carpenter
/*
* Copyright (C) 2021 Oracle.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version 2
* of the License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, see http://www.gnu.org/copyleft/gpl.txt
*/
#include "smatch.h"
static int my_id;
STATE(managed);
static void set_ignore(struct sm_state *sm, struct expression *mod_expr)
{
set_state(my_id, sm->name, sm->sym, &undefined);
}
static void match_put_device(const char *fn, struct expression *expr, void *param)
{
struct expression *arg;
arg = get_argument_from_call_expr(expr->args, PTR_INT(param));
arg = strip_expr(arg);
if (!arg || arg->type != EXPR_PREOP || arg->op != '&')
return;
arg = strip_expr(arg->unop);
if (!arg || arg->type != EXPR_DEREF)
return;
arg = strip_expr(arg->deref);
if (arg && arg->type == EXPR_PREOP && arg->op == '*')
arg = arg->unop;
set_state_expr(my_id, arg, &managed);
}
static void match_free(const char *fn, struct expression *expr, void *param)
{
struct expression *arg;
char *name;
arg = get_argument_from_call_expr(expr->args, PTR_INT(param));
if (get_state_expr(my_id, arg) != &managed)
return;
name = expr_to_str(arg);
sm_warning("freeing device managed memory: '%s'", name);
free_string(name);
}
void check_put_device(int id)
{
my_id = id;
if (option_project != PROJ_KERNEL)
return;
add_function_hook("put_device", &match_put_device, INT_PTR(0));
add_function_hook("device_unregister", &match_put_device, INT_PTR(0));
add_function_hook("kfree", &match_free, INT_PTR(0));
add_modification_hook(my_id, &set_ignore);
}