On 1/11/21 3:45 PM, Song Liu wrote:
>
>
>> On Jan 11, 2021, at 1:58 PM, Martin Lau <[email protected]> wrote:
>>
>> On Mon, Jan 11, 2021 at 10:35:43PM +0100, KP Singh wrote:
>>> On Mon, Jan 11, 2021 at 7:57 PM Martin KaFai Lau <[email protected]> wrote:
>>>>
>>>> On Fri, Jan 08, 2021 at 03:19:47PM -0800, Song Liu wrote:
>>>>
>>>> [ ... ]
>>>>
>>>>> diff --git a/kernel/bpf/bpf_local_storage.c b/kernel/bpf/bpf_local_storage.c
>>>>> index dd5aedee99e73..9bd47ad2b26f1 100644
>>>>> --- a/kernel/bpf/bpf_local_storage.c
>>>>> +++ b/kernel/bpf/bpf_local_storage.c
>>>>> @@ -140,17 +140,18 @@ static void __bpf_selem_unlink_storage(struct bpf_local_storage_elem *selem)
>>>>> {
>>>>> struct bpf_local_storage *local_storage;
>>>>> bool free_local_storage = false;
>>>>> + unsigned long flags;
>>>>>
>>>>> if (unlikely(!selem_linked_to_storage(selem)))
>>>>> /* selem has already been unlinked from sk */
>>>>> return;
>>>>>
>>>>> local_storage = rcu_dereference(selem->local_storage);
>>>>> - raw_spin_lock_bh(&local_storage->lock);
>>>>> + raw_spin_lock_irqsave(&local_storage->lock, flags);
>>>> It will be useful to have a few words in commit message on this change
>>>> for future reference purpose.
>>>>
>>>> Please also remove the in_irq() check from bpf_sk_storage.c
>>>> to avoid confusion in the future. It probably should
>>>> be in a separate patch.
>>>>
>>>> [ ... ]
>>>>
>>>>> diff --git a/kernel/bpf/bpf_task_storage.c b/kernel/bpf/bpf_task_storage.c
>>>>> index 4ef1959a78f27..f654b56907b69 100644
>>>>> diff --git a/kernel/fork.c b/kernel/fork.c
>>>>> index 7425b3224891d..3d65c8ebfd594 100644
>>>> [ ... ]
>>>>
>>>>> --- a/kernel/fork.c
>>>>> +++ b/kernel/fork.c
>>>>> @@ -96,6 +96,7 @@
>>>>> #include <linux/kasan.h>
>>>>> #include <linux/scs.h>
>>>>> #include <linux/io_uring.h>
>>>>> +#include <linux/bpf.h>
>>>>>
>>>>> #include <asm/pgalloc.h>
>>>>> #include <linux/uaccess.h>
>>>>> @@ -734,6 +735,7 @@ void __put_task_struct(struct task_struct *tsk)
>>>>> cgroup_free(tsk);
>>>>> task_numa_free(tsk, true);
>>>>> security_task_free(tsk);
>>>>> + bpf_task_storage_free(tsk);
>>>>> exit_creds(tsk);
>>>> If exit_creds() is traced by a bpf and this bpf is doing
>>>> bpf_task_storage_get(..., BPF_LOCAL_STORAGE_GET_F_CREATE),
>>>> new task storage will be created after bpf_task_storage_free().
>>>>
>>>> I recalled there was an earlier discussion with KP and KP mentioned
>>>> BPF_LSM will not be called with a task that is going away.
>>>> It seems enabling bpf task storage in bpf tracing will break
>>>> this assumption and needs to be addressed?
>>>
>>> For tracing programs, I think we will need an allow list where
>>> task local storage can be used.
>> Instead of whitelist, can refcount_inc_not_zero(&tsk->usage) be used?
>
> I think we can put refcount_inc_not_zero() in bpf_task_storage_get, like:
>
> diff --git i/kernel/bpf/bpf_task_storage.c w/kernel/bpf/bpf_task_storage.c
> index f654b56907b69..93d01b0a010e6 100644
> --- i/kernel/bpf/bpf_task_storage.c
> +++ w/kernel/bpf/bpf_task_storage.c
> @@ -216,6 +216,9 @@ BPF_CALL_4(bpf_task_storage_get, struct bpf_map *, map, struct task_struct *,
> * by an RCU read-side critical section.
> */
> if (flags & BPF_LOCAL_STORAGE_GET_F_CREATE) {
> + if (!refcount_inc_not_zero(&task->usage))
> + return -EBUSY;
> +
> sdata = bpf_local_storage_update(
> task, (struct bpf_local_storage_map *)map, value,
> BPF_NOEXIST);
>
> But where shall we add the refcount_dec()? IIUC, we cannot add it to
> __put_task_struct().
Maybe put_task_struct()?
> Thanks,
> Song
>
On Tue, Jan 12, 2021 at 5:32 PM Yonghong Song <[email protected]> wrote:
>
>
>
> On 1/11/21 3:45 PM, Song Liu wrote:
> >
> >
> >> On Jan 11, 2021, at 1:58 PM, Martin Lau <[email protected]> wrote:
> >>
> >> On Mon, Jan 11, 2021 at 10:35:43PM +0100, KP Singh wrote:
> >>> On Mon, Jan 11, 2021 at 7:57 PM Martin KaFai Lau <[email protected]> wrote:
> >>>>
> >>>> On Fri, Jan 08, 2021 at 03:19:47PM -0800, Song Liu wrote:
> >>>>
> >>>> [ ... ]
> >>>>
> >>>>> diff --git a/kernel/bpf/bpf_local_storage.c b/kernel/bpf/bpf_local_storage.c
> >>>>> index dd5aedee99e73..9bd47ad2b26f1 100644
> >>>>> --- a/kernel/bpf/bpf_local_storage.c
> >>>>> +++ b/kernel/bpf/bpf_local_storage.c
[...]
> >>>>> +#include <linux/bpf.h>
> >>>>>
> >>>>> #include <asm/pgalloc.h>
> >>>>> #include <linux/uaccess.h>
> >>>>> @@ -734,6 +735,7 @@ void __put_task_struct(struct task_struct *tsk)
> >>>>> cgroup_free(tsk);
> >>>>> task_numa_free(tsk, true);
> >>>>> security_task_free(tsk);
> >>>>> + bpf_task_storage_free(tsk);
> >>>>> exit_creds(tsk);
> >>>> If exit_creds() is traced by a bpf and this bpf is doing
> >>>> bpf_task_storage_get(..., BPF_LOCAL_STORAGE_GET_F_CREATE),
> >>>> new task storage will be created after bpf_task_storage_free().
> >>>>
> >>>> I recalled there was an earlier discussion with KP and KP mentioned
> >>>> BPF_LSM will not be called with a task that is going away.
> >>>> It seems enabling bpf task storage in bpf tracing will break
> >>>> this assumption and needs to be addressed?
> >>>
> >>> For tracing programs, I think we will need an allow list where
> >>> task local storage can be used.
> >> Instead of whitelist, can refcount_inc_not_zero(&tsk->usage) be used?
> >
> > I think we can put refcount_inc_not_zero() in bpf_task_storage_get, like:
> >
> > diff --git i/kernel/bpf/bpf_task_storage.c w/kernel/bpf/bpf_task_storage.c
> > index f654b56907b69..93d01b0a010e6 100644
> > --- i/kernel/bpf/bpf_task_storage.c
> > +++ w/kernel/bpf/bpf_task_storage.c
> > @@ -216,6 +216,9 @@ BPF_CALL_4(bpf_task_storage_get, struct bpf_map *, map, struct task_struct *,
> > * by an RCU read-side critical section.
> > */
> > if (flags & BPF_LOCAL_STORAGE_GET_F_CREATE) {
> > + if (!refcount_inc_not_zero(&task->usage))
> > + return -EBUSY;
> > +
> > sdata = bpf_local_storage_update(
> > task, (struct bpf_local_storage_map *)map, value,
> > BPF_NOEXIST);
> >
> > But where shall we add the refcount_dec()? IIUC, we cannot add it to
> > __put_task_struct().
>
> Maybe put_task_struct()?
Yeah, something like, or if you find a more elegant alternative :)
--- a/include/linux/sched/task.h
+++ b/include/linux/sched/task.h
@@ -107,13 +107,20 @@ extern void __put_task_struct(struct task_struct *t);
static inline void put_task_struct(struct task_struct *t)
{
- if (refcount_dec_and_test(&t->usage))
+
+ if (rcu_access_pointer(t->bpf_storage)) {
+ if (refcount_sub_and_test(2, &t->usage))
+ __put_task_struct(t);
+ } else if (refcount_dec_and_test(&t->usage))
__put_task_struct(t);
}
static inline void put_task_struct_many(struct task_struct *t, int nr)
{
- if (refcount_sub_and_test(nr, &t->usage))
+ if (rcu_access_pointer(t->bpf_storage)) {
+ if (refcount_sub_and_test(nr + 1, &t->usage))
+ __put_task_struct(t);
+ } else if (refcount_sub_and_test(nr, &t->usage))
__put_task_struct(t);
}
I may be missing something but shouldn't bpf_storage be an __rcu
member like we have for sk_bpf_storage?
#ifdef CONFIG_BPF_SYSCALL
struct bpf_local_storage __rcu *sk_bpf_storage;
#endif
>
> > Thanks,
> > Song
> >
> On Jan 12, 2021, at 8:53 AM, KP Singh <[email protected]> wrote:
>
> On Tue, Jan 12, 2021 at 5:32 PM Yonghong Song <[email protected]> wrote:
>>
>>
>>
>> On 1/11/21 3:45 PM, Song Liu wrote:
>>>
>>>
>>>> On Jan 11, 2021, at 1:58 PM, Martin Lau <[email protected]> wrote:
>>>>
>>>> On Mon, Jan 11, 2021 at 10:35:43PM +0100, KP Singh wrote:
>>>>> On Mon, Jan 11, 2021 at 7:57 PM Martin KaFai Lau <[email protected]> wrote:
>>>>>>
>>>>>> On Fri, Jan 08, 2021 at 03:19:47PM -0800, Song Liu wrote:
>>>>>>
>>>>>> [ ... ]
>>>>>>
>>>>>>> diff --git a/kernel/bpf/bpf_local_storage.c b/kernel/bpf/bpf_local_storage.c
>>>>>>> index dd5aedee99e73..9bd47ad2b26f1 100644
>>>>>>> --- a/kernel/bpf/bpf_local_storage.c
>>>>>>> +++ b/kernel/bpf/bpf_local_storage.c
>
> [...]
>
>>>>>>> +#include <linux/bpf.h>
>>>>>>>
>>>>>>> #include <asm/pgalloc.h>
>>>>>>> #include <linux/uaccess.h>
>>>>>>> @@ -734,6 +735,7 @@ void __put_task_struct(struct task_struct *tsk)
>>>>>>> cgroup_free(tsk);
>>>>>>> task_numa_free(tsk, true);
>>>>>>> security_task_free(tsk);
>>>>>>> + bpf_task_storage_free(tsk);
>>>>>>> exit_creds(tsk);
>>>>>> If exit_creds() is traced by a bpf and this bpf is doing
>>>>>> bpf_task_storage_get(..., BPF_LOCAL_STORAGE_GET_F_CREATE),
>>>>>> new task storage will be created after bpf_task_storage_free().
>>>>>>
>>>>>> I recalled there was an earlier discussion with KP and KP mentioned
>>>>>> BPF_LSM will not be called with a task that is going away.
>>>>>> It seems enabling bpf task storage in bpf tracing will break
>>>>>> this assumption and needs to be addressed?
>>>>>
>>>>> For tracing programs, I think we will need an allow list where
>>>>> task local storage can be used.
>>>> Instead of whitelist, can refcount_inc_not_zero(&tsk->usage) be used?
>>>
>>> I think we can put refcount_inc_not_zero() in bpf_task_storage_get, like:
>>>
>>> diff --git i/kernel/bpf/bpf_task_storage.c w/kernel/bpf/bpf_task_storage.c
>>> index f654b56907b69..93d01b0a010e6 100644
>>> --- i/kernel/bpf/bpf_task_storage.c
>>> +++ w/kernel/bpf/bpf_task_storage.c
>>> @@ -216,6 +216,9 @@ BPF_CALL_4(bpf_task_storage_get, struct bpf_map *, map, struct task_struct *,
>>> * by an RCU read-side critical section.
>>> */
>>> if (flags & BPF_LOCAL_STORAGE_GET_F_CREATE) {
>>> + if (!refcount_inc_not_zero(&task->usage))
>>> + return -EBUSY;
>>> +
>>> sdata = bpf_local_storage_update(
>>> task, (struct bpf_local_storage_map *)map, value,
>>> BPF_NOEXIST);
>>>
>>> But where shall we add the refcount_dec()? IIUC, we cannot add it to
>>> __put_task_struct().
>>
>> Maybe put_task_struct()?
>
> Yeah, something like, or if you find a more elegant alternative :)
>
> --- a/include/linux/sched/task.h
> +++ b/include/linux/sched/task.h
> @@ -107,13 +107,20 @@ extern void __put_task_struct(struct task_struct *t);
>
> static inline void put_task_struct(struct task_struct *t)
> {
> - if (refcount_dec_and_test(&t->usage))
> +
> + if (rcu_access_pointer(t->bpf_storage)) {
> + if (refcount_sub_and_test(2, &t->usage))
> + __put_task_struct(t);
> + } else if (refcount_dec_and_test(&t->usage))
> __put_task_struct(t);
> }
>
> static inline void put_task_struct_many(struct task_struct *t, int nr)
> {
> - if (refcount_sub_and_test(nr, &t->usage))
> + if (rcu_access_pointer(t->bpf_storage)) {
> + if (refcount_sub_and_test(nr + 1, &t->usage))
> + __put_task_struct(t);
> + } else if (refcount_sub_and_test(nr, &t->usage))
> __put_task_struct(t);
> }
It is not ideal to leak bpf_storage here. How about we only add the
following:
diff --git i/kernel/bpf/bpf_task_storage.c w/kernel/bpf/bpf_task_storage.c
index f654b56907b69..2811b9fc47233 100644
--- i/kernel/bpf/bpf_task_storage.c
+++ w/kernel/bpf/bpf_task_storage.c
@@ -216,6 +216,10 @@ BPF_CALL_4(bpf_task_storage_get, struct bpf_map *, map, struct task_struct *,
* by an RCU read-side critical section.
*/
if (flags & BPF_LOCAL_STORAGE_GET_F_CREATE) {
+ /* the task_struct is being freed, fail over*/
+ if (!refcount_read(&task->usage))
+ return -EBUSY;
+
sdata = bpf_local_storage_update(
task, (struct bpf_local_storage_map *)map, value,
BPF_NOEXIST);
>
>
> I may be missing something but shouldn't bpf_storage be an __rcu
> member like we have for sk_bpf_storage?
Good catch! I will fix this in v2.
Thanks,
Song
On 1/15/21 3:34 PM, Song Liu wrote:
>
>
>> On Jan 12, 2021, at 8:53 AM, KP Singh <[email protected]> wrote:
>>
>> On Tue, Jan 12, 2021 at 5:32 PM Yonghong Song <[email protected]> wrote:
>>>
>>>
>>>
>>> On 1/11/21 3:45 PM, Song Liu wrote:
>>>>
>>>>
>>>>> On Jan 11, 2021, at 1:58 PM, Martin Lau <[email protected]> wrote:
>>>>>
>>>>> On Mon, Jan 11, 2021 at 10:35:43PM +0100, KP Singh wrote:
>>>>>> On Mon, Jan 11, 2021 at 7:57 PM Martin KaFai Lau <[email protected]> wrote:
>>>>>>>
>>>>>>> On Fri, Jan 08, 2021 at 03:19:47PM -0800, Song Liu wrote:
>>>>>>>
>>>>>>> [ ... ]
>>>>>>>
>>>>>>>> diff --git a/kernel/bpf/bpf_local_storage.c b/kernel/bpf/bpf_local_storage.c
>>>>>>>> index dd5aedee99e73..9bd47ad2b26f1 100644
>>>>>>>> --- a/kernel/bpf/bpf_local_storage.c
>>>>>>>> +++ b/kernel/bpf/bpf_local_storage.c
>>
>> [...]
>>
>>>>>>>> +#include <linux/bpf.h>
>>>>>>>>
>>>>>>>> #include <asm/pgalloc.h>
>>>>>>>> #include <linux/uaccess.h>
>>>>>>>> @@ -734,6 +735,7 @@ void __put_task_struct(struct task_struct *tsk)
>>>>>>>> cgroup_free(tsk);
>>>>>>>> task_numa_free(tsk, true);
>>>>>>>> security_task_free(tsk);
>>>>>>>> + bpf_task_storage_free(tsk);
>>>>>>>> exit_creds(tsk);
>>>>>>> If exit_creds() is traced by a bpf and this bpf is doing
>>>>>>> bpf_task_storage_get(..., BPF_LOCAL_STORAGE_GET_F_CREATE),
>>>>>>> new task storage will be created after bpf_task_storage_free().
>>>>>>>
>>>>>>> I recalled there was an earlier discussion with KP and KP mentioned
>>>>>>> BPF_LSM will not be called with a task that is going away.
>>>>>>> It seems enabling bpf task storage in bpf tracing will break
>>>>>>> this assumption and needs to be addressed?
>>>>>>
>>>>>> For tracing programs, I think we will need an allow list where
>>>>>> task local storage can be used.
>>>>> Instead of whitelist, can refcount_inc_not_zero(&tsk->usage) be used?
>>>>
>>>> I think we can put refcount_inc_not_zero() in bpf_task_storage_get, like:
>>>>
>>>> diff --git i/kernel/bpf/bpf_task_storage.c w/kernel/bpf/bpf_task_storage.c
>>>> index f654b56907b69..93d01b0a010e6 100644
>>>> --- i/kernel/bpf/bpf_task_storage.c
>>>> +++ w/kernel/bpf/bpf_task_storage.c
>>>> @@ -216,6 +216,9 @@ BPF_CALL_4(bpf_task_storage_get, struct bpf_map *, map, struct task_struct *,
>>>> * by an RCU read-side critical section.
>>>> */
>>>> if (flags & BPF_LOCAL_STORAGE_GET_F_CREATE) {
>>>> + if (!refcount_inc_not_zero(&task->usage))
>>>> + return -EBUSY;
>>>> +
>>>> sdata = bpf_local_storage_update(
>>>> task, (struct bpf_local_storage_map *)map, value,
>>>> BPF_NOEXIST);
>>>>
>>>> But where shall we add the refcount_dec()? IIUC, we cannot add it to
>>>> __put_task_struct().
>>>
>>> Maybe put_task_struct()?
>>
>> Yeah, something like, or if you find a more elegant alternative :)
>>
>> --- a/include/linux/sched/task.h
>> +++ b/include/linux/sched/task.h
>> @@ -107,13 +107,20 @@ extern void __put_task_struct(struct task_struct *t);
>>
>> static inline void put_task_struct(struct task_struct *t)
>> {
>> - if (refcount_dec_and_test(&t->usage))
>> +
>> + if (rcu_access_pointer(t->bpf_storage)) {
>> + if (refcount_sub_and_test(2, &t->usage))
>> + __put_task_struct(t);
>> + } else if (refcount_dec_and_test(&t->usage))
>> __put_task_struct(t);
>> }
>>
>> static inline void put_task_struct_many(struct task_struct *t, int nr)
>> {
>> - if (refcount_sub_and_test(nr, &t->usage))
>> + if (rcu_access_pointer(t->bpf_storage)) {
>> + if (refcount_sub_and_test(nr + 1, &t->usage))
>> + __put_task_struct(t);
>> + } else if (refcount_sub_and_test(nr, &t->usage))
>> __put_task_struct(t);
>> }
>
> It is not ideal to leak bpf_storage here. How about we only add the
> following:
>
> diff --git i/kernel/bpf/bpf_task_storage.c w/kernel/bpf/bpf_task_storage.c
> index f654b56907b69..2811b9fc47233 100644
> --- i/kernel/bpf/bpf_task_storage.c
> +++ w/kernel/bpf/bpf_task_storage.c
> @@ -216,6 +216,10 @@ BPF_CALL_4(bpf_task_storage_get, struct bpf_map *, map, struct task_struct *,
> * by an RCU read-side critical section.
> */
> if (flags & BPF_LOCAL_STORAGE_GET_F_CREATE) {
> + /* the task_struct is being freed, fail over*/
> + if (!refcount_read(&task->usage))
> + return -EBUSY;
This may not work? Even we check here and task->usage is not 0, it could
still become 0 immediately after the above refcount_read, right?
> +
> sdata = bpf_local_storage_update(
> task, (struct bpf_local_storage_map *)map, value,
> BPF_NOEXIST);
>
>>
>>
>> I may be missing something but shouldn't bpf_storage be an __rcu
>> member like we have for sk_bpf_storage?
>
> Good catch! I will fix this in v2.
>
> Thanks,
> Song
>
> On Jan 15, 2021, at 4:55 PM, Yonghong Song <[email protected]> wrote:
>
>
>
> On 1/15/21 3:34 PM, Song Liu wrote:
>>> On Jan 12, 2021, at 8:53 AM, KP Singh <[email protected]> wrote:
>>>
>>> On Tue, Jan 12, 2021 at 5:32 PM Yonghong Song <[email protected]> wrote:
>>>>
>>>>
>>>>
>>>> On 1/11/21 3:45 PM, Song Liu wrote:
>>>>>
>>>>>
>>>>>> On Jan 11, 2021, at 1:58 PM, Martin Lau <[email protected]> wrote:
>>>>>>
>>>>>> On Mon, Jan 11, 2021 at 10:35:43PM +0100, KP Singh wrote:
>>>>>>> On Mon, Jan 11, 2021 at 7:57 PM Martin KaFai Lau <[email protected]> wrote:
>>>>>>>>
>>>>>>>> On Fri, Jan 08, 2021 at 03:19:47PM -0800, Song Liu wrote:
>>>>>>>>
>>>>>>>> [ ... ]
>>>>>>>>
>>>>>>>>> diff --git a/kernel/bpf/bpf_local_storage.c b/kernel/bpf/bpf_local_storage.c
>>>>>>>>> index dd5aedee99e73..9bd47ad2b26f1 100644
>>>>>>>>> --- a/kernel/bpf/bpf_local_storage.c
>>>>>>>>> +++ b/kernel/bpf/bpf_local_storage.c
>>>
>>> [...]
>>>
>>>>>>>>> +#include <linux/bpf.h>
>>>>>>>>>
>>>>>>>>> #include <asm/pgalloc.h>
>>>>>>>>> #include <linux/uaccess.h>
>>>>>>>>> @@ -734,6 +735,7 @@ void __put_task_struct(struct task_struct *tsk)
>>>>>>>>> cgroup_free(tsk);
>>>>>>>>> task_numa_free(tsk, true);
>>>>>>>>> security_task_free(tsk);
>>>>>>>>> + bpf_task_storage_free(tsk);
>>>>>>>>> exit_creds(tsk);
>>>>>>>> If exit_creds() is traced by a bpf and this bpf is doing
>>>>>>>> bpf_task_storage_get(..., BPF_LOCAL_STORAGE_GET_F_CREATE),
>>>>>>>> new task storage will be created after bpf_task_storage_free().
>>>>>>>>
>>>>>>>> I recalled there was an earlier discussion with KP and KP mentioned
>>>>>>>> BPF_LSM will not be called with a task that is going away.
>>>>>>>> It seems enabling bpf task storage in bpf tracing will break
>>>>>>>> this assumption and needs to be addressed?
>>>>>>>
>>>>>>> For tracing programs, I think we will need an allow list where
>>>>>>> task local storage can be used.
>>>>>> Instead of whitelist, can refcount_inc_not_zero(&tsk->usage) be used?
>>>>>
>>>>> I think we can put refcount_inc_not_zero() in bpf_task_storage_get, like:
>>>>>
>>>>> diff --git i/kernel/bpf/bpf_task_storage.c w/kernel/bpf/bpf_task_storage.c
>>>>> index f654b56907b69..93d01b0a010e6 100644
>>>>> --- i/kernel/bpf/bpf_task_storage.c
>>>>> +++ w/kernel/bpf/bpf_task_storage.c
>>>>> @@ -216,6 +216,9 @@ BPF_CALL_4(bpf_task_storage_get, struct bpf_map *, map, struct task_struct *,
>>>>> * by an RCU read-side critical section.
>>>>> */
>>>>> if (flags & BPF_LOCAL_STORAGE_GET_F_CREATE) {
>>>>> + if (!refcount_inc_not_zero(&task->usage))
>>>>> + return -EBUSY;
>>>>> +
>>>>> sdata = bpf_local_storage_update(
>>>>> task, (struct bpf_local_storage_map *)map, value,
>>>>> BPF_NOEXIST);
>>>>>
>>>>> But where shall we add the refcount_dec()? IIUC, we cannot add it to
>>>>> __put_task_struct().
>>>>
>>>> Maybe put_task_struct()?
>>>
>>> Yeah, something like, or if you find a more elegant alternative :)
>>>
>>> --- a/include/linux/sched/task.h
>>> +++ b/include/linux/sched/task.h
>>> @@ -107,13 +107,20 @@ extern void __put_task_struct(struct task_struct *t);
>>>
>>> static inline void put_task_struct(struct task_struct *t)
>>> {
>>> - if (refcount_dec_and_test(&t->usage))
>>> +
>>> + if (rcu_access_pointer(t->bpf_storage)) {
>>> + if (refcount_sub_and_test(2, &t->usage))
>>> + __put_task_struct(t);
>>> + } else if (refcount_dec_and_test(&t->usage))
>>> __put_task_struct(t);
>>> }
>>>
>>> static inline void put_task_struct_many(struct task_struct *t, int nr)
>>> {
>>> - if (refcount_sub_and_test(nr, &t->usage))
>>> + if (rcu_access_pointer(t->bpf_storage)) {
>>> + if (refcount_sub_and_test(nr + 1, &t->usage))
>>> + __put_task_struct(t);
>>> + } else if (refcount_sub_and_test(nr, &t->usage))
>>> __put_task_struct(t);
>>> }
>> It is not ideal to leak bpf_storage here. How about we only add the
>> following:
>> diff --git i/kernel/bpf/bpf_task_storage.c w/kernel/bpf/bpf_task_storage.c
>> index f654b56907b69..2811b9fc47233 100644
>> --- i/kernel/bpf/bpf_task_storage.c
>> +++ w/kernel/bpf/bpf_task_storage.c
>> @@ -216,6 +216,10 @@ BPF_CALL_4(bpf_task_storage_get, struct bpf_map *, map, struct task_struct *,
>> * by an RCU read-side critical section.
>> */
>> if (flags & BPF_LOCAL_STORAGE_GET_F_CREATE) {
>> + /* the task_struct is being freed, fail over*/
>> + if (!refcount_read(&task->usage))
>> + return -EBUSY;
>
> This may not work? Even we check here and task->usage is not 0, it could still become 0 immediately after the above refcount_read, right?
We call bpf_task_storage_get() with "task" that has valid BTF, so "task"
should not go away during the BPF program? Whatever mechanism that
triggers the BPF program should either hold a reference to task (usage > 0)
or be the only one owning it (usage == 0, in __put_task_struct). Did I miss
anything?
Thanks,
Song
>
>> +
>> sdata = bpf_local_storage_update(
>> task, (struct bpf_local_storage_map *)map, value,
>> BPF_NOEXIST);
>>>
>>>
>>> I may be missing something but shouldn't bpf_storage be an __rcu
>>> member like we have for sk_bpf_storage?
>> Good catch! I will fix this in v2.
>> Thanks,
>> Song
On 1/15/21 5:12 PM, Song Liu wrote:
>
>
>> On Jan 15, 2021, at 4:55 PM, Yonghong Song <[email protected]> wrote:
>>
>>
>>
>> On 1/15/21 3:34 PM, Song Liu wrote:
>>>> On Jan 12, 2021, at 8:53 AM, KP Singh <[email protected]> wrote:
>>>>
>>>> On Tue, Jan 12, 2021 at 5:32 PM Yonghong Song <[email protected]> wrote:
>>>>>
>>>>>
>>>>>
>>>>> On 1/11/21 3:45 PM, Song Liu wrote:
>>>>>>
>>>>>>
>>>>>>> On Jan 11, 2021, at 1:58 PM, Martin Lau <[email protected]> wrote:
>>>>>>>
>>>>>>> On Mon, Jan 11, 2021 at 10:35:43PM +0100, KP Singh wrote:
>>>>>>>> On Mon, Jan 11, 2021 at 7:57 PM Martin KaFai Lau <[email protected]> wrote:
>>>>>>>>>
>>>>>>>>> On Fri, Jan 08, 2021 at 03:19:47PM -0800, Song Liu wrote:
>>>>>>>>>
>>>>>>>>> [ ... ]
>>>>>>>>>
>>>>>>>>>> diff --git a/kernel/bpf/bpf_local_storage.c b/kernel/bpf/bpf_local_storage.c
>>>>>>>>>> index dd5aedee99e73..9bd47ad2b26f1 100644
>>>>>>>>>> --- a/kernel/bpf/bpf_local_storage.c
>>>>>>>>>> +++ b/kernel/bpf/bpf_local_storage.c
>>>>
>>>> [...]
>>>>
>>>>>>>>>> +#include <linux/bpf.h>
>>>>>>>>>>
>>>>>>>>>> #include <asm/pgalloc.h>
>>>>>>>>>> #include <linux/uaccess.h>
>>>>>>>>>> @@ -734,6 +735,7 @@ void __put_task_struct(struct task_struct *tsk)
>>>>>>>>>> cgroup_free(tsk);
>>>>>>>>>> task_numa_free(tsk, true);
>>>>>>>>>> security_task_free(tsk);
>>>>>>>>>> + bpf_task_storage_free(tsk);
>>>>>>>>>> exit_creds(tsk);
>>>>>>>>> If exit_creds() is traced by a bpf and this bpf is doing
>>>>>>>>> bpf_task_storage_get(..., BPF_LOCAL_STORAGE_GET_F_CREATE),
>>>>>>>>> new task storage will be created after bpf_task_storage_free().
>>>>>>>>>
>>>>>>>>> I recalled there was an earlier discussion with KP and KP mentioned
>>>>>>>>> BPF_LSM will not be called with a task that is going away.
>>>>>>>>> It seems enabling bpf task storage in bpf tracing will break
>>>>>>>>> this assumption and needs to be addressed?
>>>>>>>>
>>>>>>>> For tracing programs, I think we will need an allow list where
>>>>>>>> task local storage can be used.
>>>>>>> Instead of whitelist, can refcount_inc_not_zero(&tsk->usage) be used?
>>>>>>
>>>>>> I think we can put refcount_inc_not_zero() in bpf_task_storage_get, like:
>>>>>>
>>>>>> diff --git i/kernel/bpf/bpf_task_storage.c w/kernel/bpf/bpf_task_storage.c
>>>>>> index f654b56907b69..93d01b0a010e6 100644
>>>>>> --- i/kernel/bpf/bpf_task_storage.c
>>>>>> +++ w/kernel/bpf/bpf_task_storage.c
>>>>>> @@ -216,6 +216,9 @@ BPF_CALL_4(bpf_task_storage_get, struct bpf_map *, map, struct task_struct *,
>>>>>> * by an RCU read-side critical section.
>>>>>> */
>>>>>> if (flags & BPF_LOCAL_STORAGE_GET_F_CREATE) {
>>>>>> + if (!refcount_inc_not_zero(&task->usage))
>>>>>> + return -EBUSY;
>>>>>> +
>>>>>> sdata = bpf_local_storage_update(
>>>>>> task, (struct bpf_local_storage_map *)map, value,
>>>>>> BPF_NOEXIST);
>>>>>>
>>>>>> But where shall we add the refcount_dec()? IIUC, we cannot add it to
>>>>>> __put_task_struct().
>>>>>
>>>>> Maybe put_task_struct()?
>>>>
>>>> Yeah, something like, or if you find a more elegant alternative :)
>>>>
>>>> --- a/include/linux/sched/task.h
>>>> +++ b/include/linux/sched/task.h
>>>> @@ -107,13 +107,20 @@ extern void __put_task_struct(struct task_struct *t);
>>>>
>>>> static inline void put_task_struct(struct task_struct *t)
>>>> {
>>>> - if (refcount_dec_and_test(&t->usage))
>>>> +
>>>> + if (rcu_access_pointer(t->bpf_storage)) {
>>>> + if (refcount_sub_and_test(2, &t->usage))
>>>> + __put_task_struct(t);
>>>> + } else if (refcount_dec_and_test(&t->usage))
>>>> __put_task_struct(t);
>>>> }
>>>>
>>>> static inline void put_task_struct_many(struct task_struct *t, int nr)
>>>> {
>>>> - if (refcount_sub_and_test(nr, &t->usage))
>>>> + if (rcu_access_pointer(t->bpf_storage)) {
>>>> + if (refcount_sub_and_test(nr + 1, &t->usage))
>>>> + __put_task_struct(t);
>>>> + } else if (refcount_sub_and_test(nr, &t->usage))
>>>> __put_task_struct(t);
>>>> }
>>> It is not ideal to leak bpf_storage here. How about we only add the
>>> following:
>>> diff --git i/kernel/bpf/bpf_task_storage.c w/kernel/bpf/bpf_task_storage.c
>>> index f654b56907b69..2811b9fc47233 100644
>>> --- i/kernel/bpf/bpf_task_storage.c
>>> +++ w/kernel/bpf/bpf_task_storage.c
>>> @@ -216,6 +216,10 @@ BPF_CALL_4(bpf_task_storage_get, struct bpf_map *, map, struct task_struct *,
>>> * by an RCU read-side critical section.
>>> */
>>> if (flags & BPF_LOCAL_STORAGE_GET_F_CREATE) {
>>> + /* the task_struct is being freed, fail over*/
>>> + if (!refcount_read(&task->usage))
>>> + return -EBUSY;
>>
>> This may not work? Even we check here and task->usage is not 0, it could still become 0 immediately after the above refcount_read, right?
>
> We call bpf_task_storage_get() with "task" that has valid BTF, so "task"
> should not go away during the BPF program? Whatever mechanism that
Oh, right. this is true. Otherwise, we cannot use task ptr in the helper.
> triggers the BPF program should either hold a reference to task (usage > 0)
> or be the only one owning it (usage == 0, in __put_task_struct). Did I miss
> anything?
Sorry. I think you are right. Not sure lsm requirement. There are two
more possible ways to check task is exiting which happens before
__put_task_struct():
. check task->exit_state
. check task->flags & PF_EXITING (used in bpf_trace.c)
Not sure which condition is the correct one to check.
>
> Thanks,
> Song
>
>>
>>> +
>>> sdata = bpf_local_storage_update(
>>> task, (struct bpf_local_storage_map *)map, value,
>>> BPF_NOEXIST);
>>>>
>>>>
>>>> I may be missing something but shouldn't bpf_storage be an __rcu
>>>> member like we have for sk_bpf_storage?
>>> Good catch! I will fix this in v2.
>>> Thanks,
>>> Song
>