Re: [RFC PATCH v2 next]module: Fix mod->mkobj.kobj potentially freed too early
From: Rusty Russell
Date: Tue Aug 27 2013 - 01:48:11 EST
Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> writes:
> On Thu, Aug 22, 2013 at 03:37:55PM +0800, Li Zhong wrote:
>> DEBUG_KOBJECT_RELEASE helps to find the issue attached below.
> People are starting to hit these types of issues, and I'd like to take
> this one out of the picture.
>
> Rusty, any objection to me taking this through my driver-core tree,
> where this new config option shows up?
The original fix was better.
Moving the module_kobject out and giving it its own lifetime solves this
immediate issue, but it still means there's an accessible module_kobject
around referring to a module which doesn't exist any more.
Original copied below, feel free to take it.
Cheers,
Rusty.
From: Li Zhong <zhong@xxxxxxxxxxxxxxxxxx>
Subject: module: Fix mod->mkobj.kobj potentially freed too early
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 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.
This patch tries to fix it by waiting for the mod->mkobj.kobj to be
really released in the module removing process (and some error code
paths).
[ 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>
Signed-off-by: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
---
include/linux/module.h | 1 +
kernel/module.c | 14 +++++++++++---
kernel/params.c | 7 +++++++
3 files changed, 19 insertions(+), 3 deletions(-)
diff --git a/include/linux/module.h b/include/linux/module.h
index 504035f..05f2447 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -42,6 +42,7 @@ struct module_kobject {
struct module *mod;
struct kobject *drivers_dir;
struct module_param_attrs *mp;
+ struct completion *kobj_completion;
};
struct module_attribute {
diff --git a/kernel/module.c b/kernel/module.c
index 40ee1dc..9f5ddae 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -1612,6 +1612,14 @@ static void module_remove_modinfo_attrs(struct module *mod)
kfree(mod->modinfo_attrs);
}
+static void mod_kobject_put(struct module *mod)
+{
+ DECLARE_COMPLETION_ONSTACK(c);
+ mod->mkobj.kobj_completion = &c;
+ kobject_put(&mod->mkobj.kobj);
+ wait_for_completion(&c);
+}
+
static int mod_sysfs_init(struct module *mod)
{
int err;
@@ -1639,7 +1647,7 @@ static int mod_sysfs_init(struct module *mod)
err = kobject_init_and_add(&mod->mkobj.kobj, &module_ktype, NULL,
"%s", mod->name);
if (err)
- kobject_put(&mod->mkobj.kobj);
+ mod_kobject_put(mod);
/* delay uevent until full sysfs population */
out:
@@ -1683,7 +1691,7 @@ out_unreg_param:
out_unreg_holders:
kobject_put(mod->holders_dir);
out_unreg:
- kobject_put(&mod->mkobj.kobj);
+ mod_kobject_put(mod);
out:
return err;
}
@@ -1692,7 +1700,7 @@ static void mod_sysfs_fini(struct module *mod)
{
remove_notes_attrs(mod);
remove_sect_attrs(mod);
- kobject_put(&mod->mkobj.kobj);
+ mod_kobject_put(mod);
}
#else /* !CONFIG_SYSFS */
diff --git a/kernel/params.c b/kernel/params.c
index e5f8f17..501bde4 100644
--- a/kernel/params.c
+++ b/kernel/params.c
@@ -915,7 +915,14 @@ 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);
+ complete(mk->kobj_completion);
+}
+
struct kobj_type module_ktype = {
+ .release = module_kobj_release,
.sysfs_ops = &module_sysfs_ops,
};
--
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