[RFC PATCH v2 next]module: Fix mod->mkobj.kobj potentially freedtoo early

From: Li Zhong
Date: Thu Aug 22 2013 - 03:38:13 EST

DEBUG_KOBJECT_RELEASE helps to find the issue attached below.

After some investigation, it seems the reason is:
The mod->mkobj.kobj(ffffffffa01600d0 below) is freed together with mod
itself by module_free(mod, mod->module_core) in free_module(). However,
its children still hold references to it, as the delay caused by
DEBUG_KOBJECT_RELEASE. So when the child('holders' below) tries to
decrease the reference count to its parent in kobject_del(), BUG happens
as it tries to access already freed memory.

v2:
Greg suggested to make the kobject as a pointer. But it seems a little
hard to make kobj(kobject) embedded in mkobj(module_kobject) a pointer,
as that seems to cause getting the mkobj from the kobj impossible --
to_module_kobject() is used in several places to derive mkobj from its
member kobj.

So in this version, I made the whole mkobj(module_kobject) as a pointer
in mod(module).

The mkobj is then allocated in mod_sysfs_init(), and freed in its member
kobj's release function -- it seems that there is no mkobj usage after
its kobj is released?

[ 1844.175287] kobject: 'holders' (ffff88007c1f1600): kobject_release, parent ffffffffa01600d0 (delayed)
[ 1844.178991] kobject: 'notes' (ffff8800370b2a00): kobject_release, parent ffffffffa01600d0 (delayed)
[ 1845.180118] kobject: 'holders' (ffff88007c1f1600): kobject_cleanup, parent ffffffffa01600d0
[ 1845.182130] kobject: 'holders' (ffff88007c1f1600): auto cleanup kobject_del
[ 1845.184120] BUG: unable to handle kernel paging request at ffffffffa01601d0
[ 1845.185026] IP: [<ffffffff812cda81>] kobject_put+0x11/0x60
[ 1845.185026] PGD 1a13067 PUD 1a14063 PMD 7bd30067 PTE 0
[ 1845.185026] Oops: 0000 [#1] PREEMPT
[ 1845.185026] Modules linked in: xfs libcrc32c [last unloaded: kprobe_example]
[ 1845.185026] CPU: 0 PID: 18 Comm: kworker/0:1 Tainted: G O 3.11.0-rc6-next-20130819+ #1
[ 1845.185026] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2007
[ 1845.185026] Workqueue: events kobject_delayed_cleanup
[ 1845.185026] task: ffff88007ca51f00 ti: ffff88007ca5c000 task.ti: ffff88007ca5c000
[ 1845.185026] RIP: 0010:[<ffffffff812cda81>] [<ffffffff812cda81>] kobject_put+0x11/0x60
[ 1845.185026] RSP: 0018:ffff88007ca5dd08 EFLAGS: 00010282
[ 1845.185026] RAX: 0000000000002000 RBX: ffffffffa01600d0 RCX: ffffffff8177d638
[ 1845.185026] RDX: ffff88007ca5dc18 RSI: 0000000000000000 RDI: ffffffffa01600d0
[ 1845.185026] RBP: ffff88007ca5dd18 R08: ffffffff824e9810 R09: ffffffffffffffff
[ 1845.185026] R10: ffff8800ffffffff R11: dead4ead00000001 R12: ffffffff81a95040
[ 1845.185026] R13: ffff88007b27a960 R14: ffff88007c1f1600 R15: 0000000000000000
[ 1845.185026] FS: 0000000000000000(0000) GS:ffffffff81a23000(0000) knlGS:0000000000000000
[ 1845.185026] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[ 1845.185026] CR2: ffffffffa01601d0 CR3: 0000000037207000 CR4: 00000000000006b0
[ 1845.185026] Stack:
[ 1845.185026] ffff88007c1f1600 ffff88007c1f1600 ffff88007ca5dd38 ffffffff812cdb7e
[ 1845.185026] 0000000000000000 ffff88007c1f1640 ffff88007ca5dd68 ffffffff812cdbfe
[ 1845.185026] ffff88007c974800 ffff88007c1f1640 ffff88007ff61a00 0000000000000000
[ 1845.185026] Call Trace:
[ 1845.185026] [<ffffffff812cdb7e>] kobject_del+0x2e/0x40
[ 1845.185026] [<ffffffff812cdbfe>] kobject_delayed_cleanup+0x6e/0x1d0
[ 1845.185026] [<ffffffff81063a45>] process_one_work+0x1e5/0x670
[ 1845.185026] [<ffffffff810639e3>] ? process_one_work+0x183/0x670
[ 1845.185026] [<ffffffff810642b3>] worker_thread+0x113/0x370
[ 1845.185026] [<ffffffff810641a0>] ? rescuer_thread+0x290/0x290
[ 1845.185026] [<ffffffff8106bfba>] kthread+0xda/0xe0
[ 1845.185026] [<ffffffff814ff0f0>] ? _raw_spin_unlock_irq+0x30/0x60
[ 1845.185026] [<ffffffff8106bee0>] ? kthread_create_on_node+0x130/0x130
[ 1845.185026] [<ffffffff8150751a>] ret_from_fork+0x7a/0xb0
[ 1845.185026] [<ffffffff8106bee0>] ? kthread_create_on_node+0x130/0x130
[ 1845.185026] Code: 81 48 c7 c7 28 95 ad 81 31 c0 e8 9b da 01 00 e9 4f ff ff ff 66 0f 1f 44 00 00 55 48 89 e5 53 48 89 fb 48 83 ec 08 48 85 ff 74 1d <f6> 87 00 01 00 00 01 74 1e 48 8d 7b 38 83 6b 38 01 0f 94 c0 84
[ 1845.185026] RIP [<ffffffff812cda81>] kobject_put+0x11/0x60
[ 1845.185026] RSP <ffff88007ca5dd08>
[ 1845.185026] CR2: ffffffffa01601d0
[ 1845.185026] ---[ end trace 49a70afd109f5653 ]---

Signed-off-by: Li Zhong <zhong@xxxxxxxxxxxxxxxxxx>
---
drivers/base/core.c | 2 +-
drivers/base/module.c | 4 ++--
include/linux/module.h | 2 +-
kernel/module.c | 37 +++++++++++++++++++++----------------
kernel/params.c | 19 +++++++++++++------
5 files changed, 38 insertions(+), 26 deletions(-)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index 09a99d6..b8a1fc6 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -1629,7 +1629,7 @@ struct device *__root_device_register(const char *name, struct module *owner)

#ifdef CONFIG_MODULES /* gotta find a "cleaner" way to do this */
if (owner) {
- struct module_kobject *mk = &owner->mkobj;
+ struct module_kobject *mk = owner->mkobj;

err = sysfs_create_link(&root->dev.kobj, &mk->kobj, "module");
if (err) {
diff --git a/drivers/base/module.c b/drivers/base/module.c
index db930d3..7b7bd5a 100644
--- a/drivers/base/module.c
+++ b/drivers/base/module.c
@@ -40,7 +40,7 @@ void module_add_driver(struct module *mod, struct device_driver *drv)
return;

if (mod)
- mk = &mod->mkobj;
+ mk = mod->mkobj;
else if (drv->mod_name) {
struct kobject *mkobj;

@@ -80,7 +80,7 @@ void module_remove_driver(struct device_driver *drv)
sysfs_remove_link(&drv->p->kobj, "module");

if (drv->owner)
- mk = &drv->owner->mkobj;
+ mk = drv->owner->mkobj;
else if (drv->p->mkobj)
mk = drv->p->mkobj;
if (mk && mk->drivers_dir) {
diff --git a/include/linux/module.h b/include/linux/module.h
index 504035f..a499db6 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -236,7 +236,7 @@ struct module
char name[MODULE_NAME_LEN];

/* Sysfs stuff. */
- struct module_kobject mkobj;
+ struct module_kobject *mkobj;
struct module_attribute *modinfo_attrs;
const char *version;
const char *srcversion;
diff --git a/kernel/module.c b/kernel/module.c
index 2069158..48060b4 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -1402,7 +1402,7 @@ static void add_sect_attrs(struct module *mod, const struct load_info *info)
}
*gattr = NULL;

- if (sysfs_create_group(&mod->mkobj.kobj, &sect_attrs->grp))
+ if (sysfs_create_group(&mod->mkobj->kobj, &sect_attrs->grp))
goto out;

mod->sect_attrs = sect_attrs;
@@ -1414,7 +1414,7 @@ static void add_sect_attrs(struct module *mod, const struct load_info *info)
static void remove_sect_attrs(struct module *mod)
{
if (mod->sect_attrs) {
- sysfs_remove_group(&mod->mkobj.kobj,
+ sysfs_remove_group(&mod->mkobj->kobj,
&mod->sect_attrs->grp);
/* We are positive that no one is using any sect attrs
* at this point. Deallocate immediately. */
@@ -1499,7 +1499,7 @@ static void add_notes_attrs(struct module *mod, const struct load_info *info)
++loaded;
}

- notes_attrs->dir = kobject_create_and_add("notes", &mod->mkobj.kobj);
+ notes_attrs->dir = kobject_create_and_add("notes", &mod->mkobj->kobj);
if (!notes_attrs->dir)
goto out;

@@ -1551,7 +1551,7 @@ static void add_usage_links(struct module *mod)
mutex_lock(&module_mutex);
list_for_each_entry(use, &mod->target_list, target_list) {
nowarn = sysfs_create_link(use->target->holders_dir,
- &mod->mkobj.kobj, mod->name);
+ &mod->mkobj->kobj, mod->name);
}
mutex_unlock(&module_mutex);
#endif
@@ -1588,7 +1588,8 @@ static int module_add_modinfo_attrs(struct module *mod)
(attr->test && attr->test(mod))) {
memcpy(temp_attr, attr, sizeof(*temp_attr));
sysfs_attr_init(&temp_attr->attr);
- error = sysfs_create_file(&mod->mkobj.kobj,&temp_attr->attr);
+ error = sysfs_create_file(&mod->mkobj->kobj,
+ &temp_attr->attr);
++temp_attr;
}
}
@@ -1604,7 +1605,7 @@ static void module_remove_modinfo_attrs(struct module *mod)
/* pick a field to test for end of list */
if (!attr->attr.name)
break;
- sysfs_remove_file(&mod->mkobj.kobj,&attr->attr);
+ sysfs_remove_file(&mod->mkobj->kobj, &attr->attr);
if (attr->free)
attr->free(mod);
}
@@ -1630,15 +1631,19 @@ static int mod_sysfs_init(struct module *mod)
err = -EINVAL;
goto out;
}
+ mod->mkobj = kzalloc(sizeof(*mod->mkobj), GFP_KERNEL);
+ if (!mod->mkobj) {
+ err = -ENOMEM;
+ goto out;
+ }

- mod->mkobj.mod = mod;
+ mod->mkobj->mod = mod;

- memset(&mod->mkobj.kobj, 0, sizeof(mod->mkobj.kobj));
- mod->mkobj.kobj.kset = module_kset;
- err = kobject_init_and_add(&mod->mkobj.kobj, &module_ktype, NULL,
+ mod->mkobj->kobj.kset = module_kset;
+ err = kobject_init_and_add(&mod->mkobj->kobj, &module_ktype, NULL,
"%s", mod->name);
if (err)
- kobject_put(&mod->mkobj.kobj);
+ kobject_put(&mod->mkobj->kobj);

/* delay uevent until full sysfs population */
out:
@@ -1656,7 +1661,7 @@ static int mod_sysfs_setup(struct module *mod,
if (err)
goto out;

- mod->holders_dir = kobject_create_and_add("holders", &mod->mkobj.kobj);
+ mod->holders_dir = kobject_create_and_add("holders", &mod->mkobj->kobj);
if (!mod->holders_dir) {
err = -ENOMEM;
goto out_unreg;
@@ -1674,7 +1679,7 @@ static int mod_sysfs_setup(struct module *mod,
add_sect_attrs(mod, info);
add_notes_attrs(mod, info);

- kobject_uevent(&mod->mkobj.kobj, KOBJ_ADD);
+ kobject_uevent(&mod->mkobj->kobj, KOBJ_ADD);
return 0;

out_unreg_param:
@@ -1682,7 +1687,7 @@ out_unreg_param:
out_unreg_holders:
kobject_put(mod->holders_dir);
out_unreg:
- kobject_put(&mod->mkobj.kobj);
+ kobject_put(&mod->mkobj->kobj);
out:
return err;
}
@@ -1691,7 +1696,7 @@ static void mod_sysfs_fini(struct module *mod)
{
remove_notes_attrs(mod);
remove_sect_attrs(mod);
- kobject_put(&mod->mkobj.kobj);
+ kobject_put(&mod->mkobj->kobj);
}

#else /* !CONFIG_SYSFS */
@@ -1723,7 +1728,7 @@ static void mod_sysfs_teardown(struct module *mod)
del_usage_links(mod);
module_remove_modinfo_attrs(mod);
module_param_sysfs_remove(mod);
- kobject_put(mod->mkobj.drivers_dir);
+ kobject_put(mod->mkobj->drivers_dir);
kobject_put(mod->holders_dir);
mod_sysfs_fini(mod);
}
diff --git a/kernel/params.c b/kernel/params.c
index 1f228a3..6bce9db 100644
--- a/kernel/params.c
+++ b/kernel/params.c
@@ -684,7 +684,7 @@ int module_param_sysfs_setup(struct module *mod,
for (i = 0; i < num_params; i++) {
if (kparam[i].perm == 0)
continue;
- err = add_sysfs_param(&mod->mkobj, &kparam[i], kparam[i].name);
+ err = add_sysfs_param(mod->mkobj, &kparam[i], kparam[i].name);
if (err)
return err;
params = true;
@@ -694,9 +694,9 @@ int module_param_sysfs_setup(struct module *mod,
return 0;

/* Create the param group. */
- err = sysfs_create_group(&mod->mkobj.kobj, &mod->mkobj.mp->grp);
+ err = sysfs_create_group(&mod->mkobj->kobj, &mod->mkobj->mp->grp);
if (err)
- free_module_param_attrs(&mod->mkobj);
+ free_module_param_attrs(mod->mkobj);
return err;
}

@@ -709,11 +709,11 @@ int module_param_sysfs_setup(struct module *mod,
*/
void module_param_sysfs_remove(struct module *mod)
{
- if (mod->mkobj.mp) {
- sysfs_remove_group(&mod->mkobj.kobj, &mod->mkobj.mp->grp);
+ if (mod->mkobj->mp) {
+ sysfs_remove_group(&mod->mkobj->kobj, &mod->mkobj->mp->grp);
/* We are positive that no one is using any param
* attrs at this point. Deallocate immediately. */
- free_module_param_attrs(&mod->mkobj);
+ free_module_param_attrs(mod->mkobj);
}
}
#endif
@@ -912,7 +912,14 @@ static const struct kset_uevent_ops module_uevent_ops = {
struct kset *module_kset;
int module_sysfs_initialized;

+static void module_kobj_release(struct kobject *kobj)
+{
+ struct module_kobject *mk = to_module_kobject(kobj);
+ kfree(mk);
+}
+
struct kobj_type module_ktype = {
+ .release = module_kobj_release,
.sysfs_ops = &module_sysfs_ops,
};



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