kernel/workqueue.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-)
Currently, for UNBOUND workqueue allocation failure, the
apply_wqattr_cleanup() will be called and use the pwq_release_worker
kthread to release resources asynchronously. however, the kfree(wq)
is invoked directly in failure path of alloc_workqueue(), this leads
to the following scenario:
BUG: KASAN: slab-use-after-free in pwq_release_workfn+0x339/0x380 kernel/workqueue.c:4124
Read of size 4 at addr ffff888027b831c0 by task pool_workqueue_/3
CPU: 0 PID: 3 Comm: pool_workqueue_ Not tainted 6.5.0-rc7-next-20230825-syzkaller #0
Hardware name: Google Compute Engine/Google Compute Engine, BIOS Google 07/26/2023
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0xd9/0x1b0 lib/dump_stack.c:106
print_address_description mm/kasan/report.c:364 [inline]
print_report+0xc4/0x620 mm/kasan/report.c:475
kasan_report+0xda/0x110 mm/kasan/report.c:588
pwq_release_workfn+0x339/0x380 kernel/workqueue.c:4124
kthread_worker_fn+0x2fc/0xa80 kernel/kthread.c:823
kthread+0x33a/0x430 kernel/kthread.c:388
ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:304
</TASK>
Allocated by task 5054:
kasan_save_stack+0x33/0x50 mm/kasan/common.c:45
kasan_set_track+0x25/0x30 mm/kasan/common.c:52
____kasan_kmalloc mm/kasan/common.c:374 [inline]
__kasan_kmalloc+0xa2/0xb0 mm/kasan/common.c:383
kmalloc include/linux/slab.h:599 [inline]
kzalloc include/linux/slab.h:720 [inline]
alloc_workqueue+0x16f/0x1490 kernel/workqueue.c:4684
kvm_mmu_init_tdp_mmu+0x23/0x100 arch/x86/kvm/mmu/tdp_mmu.c:19
kvm_mmu_init_vm+0x248/0x2e0 arch/x86/kvm/mmu/mmu.c:6180
kvm_arch_init_vm+0x39/0x720 arch/x86/kvm/x86.c:12311
kvm_create_vm arch/x86/kvm/../../../virt/kvm/kvm_main.c:1222 [inline]
kvm_dev_ioctl_create_vm arch/x86/kvm/../../../virt/kvm/kvm_main.c:5089 [inline]
kvm_dev_ioctl+0xa31/0x1c20 arch/x86/kvm/../../../virt/kvm/kvm_main.c:5131
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:871 [inline]
__se_sys_ioctl fs/ioctl.c:857 [inline]
__x64_sys_ioctl+0x18f/0x210 fs/ioctl.c:857
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x38/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
Freed by task 5054:
kasan_save_stack+0x33/0x50 mm/kasan/common.c:45
kasan_set_track+0x25/0x30 mm/kasan/common.c:52
kasan_save_free_info+0x2b/0x40 mm/kasan/generic.c:522
____kasan_slab_free mm/kasan/common.c:236 [inline]
____kasan_slab_free+0x15b/0x1b0 mm/kasan/common.c:200
kasan_slab_free include/linux/kasan.h:164 [inline]
slab_free_hook mm/slub.c:1800 [inline]
slab_free_freelist_hook+0x114/0x1e0 mm/slub.c:1826
slab_free mm/slub.c:3809 [inline]
__kmem_cache_free+0xb8/0x2f0 mm/slub.c:3822
alloc_workqueue+0xe76/0x1490 kernel/workqueue.c:4746
kvm_mmu_init_tdp_mmu+0x23/0x100 arch/x86/kvm/mmu/tdp_mmu.c:19
kvm_mmu_init_vm+0x248/0x2e0 arch/x86/kvm/mmu/mmu.c:6180
kvm_arch_init_vm+0x39/0x720 arch/x86/kvm/x86.c:12311
kvm_create_vm arch/x86/kvm/../../../virt/kvm/kvm_main.c:1222 [inline]
kvm_dev_ioctl_create_vm arch/x86/kvm/../../../virt/kvm/kvm_main.c:5089 [inline]
kvm_dev_ioctl+0xa31/0x1c20 arch/x86/kvm/../../../virt/kvm/kvm_main.c:5131
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:871 [inline]
__se_sys_ioctl fs/ioctl.c:857 [inline]
__x64_sys_ioctl+0x18f/0x210 fs/ioctl.c:857
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x38/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
This commit therefore only direct release resources when the
!UNBOUND workqueue allocation failure.
Reported-by: syzbot+60db9f652c92d5bacba4@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=60db9f652c92d5bacba4
Signed-off-by: Zqiang <qiang.zhang1211@gmail.com>
---
kernel/workqueue.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index c85825e17df8..f3f9c9222070 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -4609,6 +4609,10 @@ static int alloc_and_link_pwqs(struct workqueue_struct *wq)
free_percpu(wq->cpu_pwq);
wq->cpu_pwq = NULL;
}
+ wq_unregister_lockdep(wq);
+ wq_free_lockdep(wq);
+ free_workqueue_attrs(wq->unbound_attrs);
+ kfree(wq);
return -ENOMEM;
}
@@ -4712,7 +4716,7 @@ struct workqueue_struct *alloc_workqueue(const char *fmt,
INIT_LIST_HEAD(&wq->list);
if (alloc_and_link_pwqs(wq) < 0)
- goto err_unreg_lockdep;
+ return NULL;
if (wq_online && init_rescuer(wq) < 0)
goto err_destroy;
@@ -4738,11 +4742,7 @@ struct workqueue_struct *alloc_workqueue(const char *fmt,
return wq;
-err_unreg_lockdep:
- wq_unregister_lockdep(wq);
- wq_free_lockdep(wq);
err_free_wq:
- free_workqueue_attrs(wq->unbound_attrs);
kfree(wq);
return NULL;
err_destroy:
--
2.17.1Hello, On Sat, Sep 02, 2023 at 07:50:26PM +0800, Zqiang wrote: > diff --git a/kernel/workqueue.c b/kernel/workqueue.c > index c85825e17df8..f3f9c9222070 100644 > --- a/kernel/workqueue.c > +++ b/kernel/workqueue.c > @@ -4609,6 +4609,10 @@ static int alloc_and_link_pwqs(struct workqueue_struct *wq) > free_percpu(wq->cpu_pwq); > wq->cpu_pwq = NULL; > } > + wq_unregister_lockdep(wq); > + wq_free_lockdep(wq); > + free_workqueue_attrs(wq->unbound_attrs); > + kfree(wq); So, this would fix the bug but it's quite confusing because we end up taking two separate error handling paths and alloc_and_link_pwqs() ends up freeing stuff allocated outside the function. Wouldn't it be enough to flush the pwq_release_worker after apply_workqueue_attrs() failure so that the cleanup operation ordering is maintained? Thanks. -- tejun
> > Hello, > > On Sat, Sep 02, 2023 at 07:50:26PM +0800, Zqiang wrote: > > diff --git a/kernel/workqueue.c b/kernel/workqueue.c > > index c85825e17df8..f3f9c9222070 100644 > > --- a/kernel/workqueue.c > > +++ b/kernel/workqueue.c > > @@ -4609,6 +4609,10 @@ static int alloc_and_link_pwqs(struct workqueue_struct *wq) > > free_percpu(wq->cpu_pwq); > > wq->cpu_pwq = NULL; > > } > > + wq_unregister_lockdep(wq); > > + wq_free_lockdep(wq); > > + free_workqueue_attrs(wq->unbound_attrs); > > + kfree(wq); > > So, this would fix the bug but it's quite confusing because we end up taking > two separate error handling paths and alloc_and_link_pwqs() ends up freeing > stuff allocated outside the function. Wouldn't it be enough to flush the > pwq_release_worker after apply_workqueue_attrs() failure so that the cleanup > operation ordering is maintained? Hello, Tejun Flush the pwq_release_worker is insufficient, the call_rcu() is invoked to release wq in pwq_release_workfn(), this is also asynchronous. Thanks Zqiang > > Thanks. > > -- > tejun
On Wed, Sep 06, 2023 at 10:12:34AM +0800, Z qiang wrote: > Flush the pwq_release_worker is insufficient, the call_rcu() is > invoked to release wq > in pwq_release_workfn(), this is also asynchronous. But rcu_free_pwq() doesn't access wq or anything. The last access is from the work function. Thanks. -- tejun
> > On Wed, Sep 06, 2023 at 10:12:34AM +0800, Z qiang wrote: > > Flush the pwq_release_worker is insufficient, the call_rcu() is > > invoked to release wq > > in pwq_release_workfn(), this is also asynchronous. > > But rcu_free_pwq() doesn't access wq or anything. The last access is from > the work function. The rcu_free_wq() will access wq->cpu_pwq or unbound_attrs, but at this time, the kfree(wq) may have been called in alloc_workqueue(). Thanks Zqiang > > Thanks. > > -- > tejun
On Thu, Sep 07, 2023 at 10:13:23AM +0800, Z qiang wrote: > > > > On Wed, Sep 06, 2023 at 10:12:34AM +0800, Z qiang wrote: > > > Flush the pwq_release_worker is insufficient, the call_rcu() is > > > invoked to release wq > > > in pwq_release_workfn(), this is also asynchronous. > > > > But rcu_free_pwq() doesn't access wq or anything. The last access is from > > the work function. > > The rcu_free_wq() will access wq->cpu_pwq or unbound_attrs, > but at this time, the kfree(wq) may have been called in alloc_workqueue(). I'm not following. The only way alloc_and_link fails is if apply_wqattrs_prepare() fails and if prepare fails, none of the pwq's are installed and pwq_unbound_release_workfn() won't try to free the wq as the pwq's don't have any reference on it. So, if you flush the pwq release work items, there can be no rcu_free_wq() in flight. Can you please try to see whether the problem is reproducible with flushing? Thanks. -- tejun
> > On Thu, Sep 07, 2023 at 10:13:23AM +0800, Z qiang wrote: > > > > > > On Wed, Sep 06, 2023 at 10:12:34AM +0800, Z qiang wrote: > > > > Flush the pwq_release_worker is insufficient, the call_rcu() is > > > > invoked to release wq > > > > in pwq_release_workfn(), this is also asynchronous. > > > > > > But rcu_free_pwq() doesn't access wq or anything. The last access is from > > > the work function. > > > > The rcu_free_wq() will access wq->cpu_pwq or unbound_attrs, > > but at this time, the kfree(wq) may have been called in alloc_workqueue(). > > I'm not following. The only way alloc_and_link fails is if > apply_wqattrs_prepare() fails and if prepare fails, none of the pwq's are > installed and pwq_unbound_release_workfn() won't try to free the wq as the > pwq's don't have any reference on it. So, if you flush the pwq release work > items, there can be no rcu_free_wq() in flight. Can you please try to see > whether the problem is reproducible with flushing? > you are right . sorry, I ignore if apply_wqattrs_prepare() fails, none of the pwq is installed, the install_unbound_pwq() is not invoked. I will resend v2 and test. Thanks Zqiang > > Thanks. > > -- > tejun
Hi qiang && Tejun
On Tue, Sep 19, 2023 at 7:30 PM Z qiang <qiang.zhang1211@gmail.com> wrote:
>
> >
> > On Thu, Sep 07, 2023 at 10:13:23AM +0800, Z qiang wrote:
> > > >
> > > > On Wed, Sep 06, 2023 at 10:12:34AM +0800, Z qiang wrote:
> > > > > Flush the pwq_release_worker is insufficient, the call_rcu() is
> > > > > invoked to release wq
> > > > > in pwq_release_workfn(), this is also asynchronous.
> > > >
> > > > But rcu_free_pwq() doesn't access wq or anything. The last access is from
> > > > the work function.
> > >
> > > The rcu_free_wq() will access wq->cpu_pwq or unbound_attrs,
> > > but at this time, the kfree(wq) may have been called in alloc_workqueue().
> >
> > I'm not following. The only way alloc_and_link fails is if
> > apply_wqattrs_prepare() fails and if prepare fails, none of the pwq's are
> > installed and pwq_unbound_release_workfn() won't try to free the wq as the
> > pwq's don't have any reference on it. So, if you flush the pwq release work
> > items, there can be no rcu_free_wq() in flight. Can you please try to see
> > whether the problem is reproducible with flushing?
> >
>
> you are right . sorry, I ignore if apply_wqattrs_prepare() fails,
> none of the pwq is installed,
> the install_unbound_pwq() is not invoked. I will resend v2 and test.
I want to ask a question, why delete the v1?
Although add the flush_work, the release work would release the lockdep key,
and at the last of alloc_workqueue, it would also unregister_lockdep_key twice.
And other question, why not free lockdep and just unregister_lockdep?
4136 if (is_last) {
4137 wq_unregister_lockdep(wq);
4138 call_rcu(&wq->rcu, rcu_free_wq);
4139 }
I would really appreciate it if you could help explain it.
Thanks!
BR
>
> Thanks
> Zqiang
>
> >
> > Thanks.
> >
> > --
> > tejun
>
> Hi qiang && Tejun
>
> On Tue, Sep 19, 2023 at 7:30 PM Z qiang <qiang.zhang1211@gmail.com> wrote:
> >
> > >
> > > On Thu, Sep 07, 2023 at 10:13:23AM +0800, Z qiang wrote:
> > > > >
> > > > > On Wed, Sep 06, 2023 at 10:12:34AM +0800, Z qiang wrote:
> > > > > > Flush the pwq_release_worker is insufficient, the call_rcu() is
> > > > > > invoked to release wq
> > > > > > in pwq_release_workfn(), this is also asynchronous.
> > > > >
> > > > > But rcu_free_pwq() doesn't access wq or anything. The last access is from
> > > > > the work function.
> > > >
> > > > The rcu_free_wq() will access wq->cpu_pwq or unbound_attrs,
> > > > but at this time, the kfree(wq) may have been called in alloc_workqueue().
> > >
> > > I'm not following. The only way alloc_and_link fails is if
> > > apply_wqattrs_prepare() fails and if prepare fails, none of the pwq's are
> > > installed and pwq_unbound_release_workfn() won't try to free the wq as the
> > > pwq's don't have any reference on it. So, if you flush the pwq release work
> > > items, there can be no rcu_free_wq() in flight. Can you please try to see
> > > whether the problem is reproducible with flushing?
> > >
> >
> > you are right . sorry, I ignore if apply_wqattrs_prepare() fails,
> > none of the pwq is installed,
> > the install_unbound_pwq() is not invoked. I will resend v2 and test.
>
> I want to ask a question, why delete the v1?
> Although add the flush_work, the release work would release the lockdep key,
> and at the last of alloc_workqueue, it would also unregister_lockdep_key twice.
>
For unbound wq, if apply_workqueue_attrs() return error, the link_pwq() will
not be invoked, that means will not insert pwq->pwqs_node to wq->pwqs list,
that also means the is_last is false in pwq_release_workfn().
> And other question, why not free lockdep and just unregister_lockdep?
>
> 4136 if (is_last) {
> 4137 wq_unregister_lockdep(wq);
> 4138 call_rcu(&wq->rcu, rcu_free_wq);
> 4139 }
free lockdep in rcu_free_wq();
Thanks
Zqiang
>
> I would really appreciate it if you could help explain it.
>
> Thanks!
> BR
>
>
>
> >
> > Thanks
> > Zqiang
> >
> > >
> > > Thanks.
> > >
> > > --
> > > tejun
> > > > > On Wed, Sep 06, 2023 at 10:12:34AM +0800, Z qiang wrote: > > > Flush the pwq_release_worker is insufficient, the call_rcu() is > > > invoked to release wq > > > in pwq_release_workfn(), this is also asynchronous. > > > > But rcu_free_pwq() doesn't access wq or anything. The last access is from > > the work function. > > The rcu_free_wq() will access wq->cpu_pwq or unbound_attrs, > but at this time, the kfree(wq) may have been called in alloc_workqueue(). > Friendly ping. Thanks Zqiang > Thanks > Zqiang > > > > > > Thanks. > > > > -- > > tejun
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