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); }