* [PATCH] kthread: Fix PF_KTHREAD vs to_kthread() race
@ 2021-08-30 11:05 Borislav Petkov
2021-08-31 6:39 ` Patrick Schaaf
2021-09-01 9:44 ` Greg KH
0 siblings, 2 replies; 4+ messages in thread
From: Borislav Petkov @ 2021-08-30 11:05 UTC (permalink / raw)
To: stable; +Cc: bugzilla.kernel.org
Hi stable folks,
please queue for 5.10-stable.
See https://bugzilla.kernel.org/show_bug.cgi?id=214159 for more info.
---
Commit 3a7956e25e1d7b3c148569e78895e1f3178122a9 upstream.
The kthread_is_per_cpu() construct relies on only being called on
PF_KTHREAD tasks (per the WARN in to_kthread). This gives rise to the
following usage pattern:
if ((p->flags & PF_KTHREAD) && kthread_is_per_cpu(p))
However, as reported by syzcaller, this is broken. The scenario is:
CPU0 CPU1 (running p)
(p->flags & PF_KTHREAD) // true
begin_new_exec()
me->flags &= ~(PF_KTHREAD|...);
kthread_is_per_cpu(p)
to_kthread(p)
WARN(!(p->flags & PF_KTHREAD) <-- *SPLAT*
Introduce __to_kthread() that omits the WARN and is sure to check both
values.
Use this to remove the problematic pattern for kthread_is_per_cpu()
and fix a number of other kthread_*() functions that have similar
issues but are currently not used in ways that would expose the
problem.
Notably kthread_func() is only ever called on 'current', while
kthread_probe_data() is only used for PF_WQ_WORKER, which implies the
task is from kthread_create*().
Fixes: ac687e6e8c26 ("kthread: Extract KTHREAD_IS_PER_CPU")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Valentin Schneider <Valentin.Schneider@arm.com>
Link: https://lkml.kernel.org/r/YH6WJc825C4P0FCK@hirez.programming.kicks-ass.net
[ Drop the balance_push() hunk as it is not needed. ]
Signed-off-by: Borislav Petkov <bp@suse.de>
---
kernel/kthread.c | 33 +++++++++++++++++++++++++++------
kernel/sched/fair.c | 2 +-
2 files changed, 28 insertions(+), 7 deletions(-)
diff --git a/kernel/kthread.c b/kernel/kthread.c
index 9825cf89c614..508fe5278285 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -84,6 +84,25 @@ static inline struct kthread *to_kthread(struct task_struct *k)
return (__force void *)k->set_child_tid;
}
+/*
+ * Variant of to_kthread() that doesn't assume @p is a kthread.
+ *
+ * Per construction; when:
+ *
+ * (p->flags & PF_KTHREAD) && p->set_child_tid
+ *
+ * the task is both a kthread and struct kthread is persistent. However
+ * PF_KTHREAD on it's own is not, kernel_thread() can exec() (See umh.c and
+ * begin_new_exec()).
+ */
+static inline struct kthread *__to_kthread(struct task_struct *p)
+{
+ void *kthread = (__force void *)p->set_child_tid;
+ if (kthread && !(p->flags & PF_KTHREAD))
+ kthread = NULL;
+ return kthread;
+}
+
void free_kthread_struct(struct task_struct *k)
{
struct kthread *kthread;
@@ -168,8 +187,9 @@ EXPORT_SYMBOL_GPL(kthread_freezable_should_stop);
*/
void *kthread_func(struct task_struct *task)
{
- if (task->flags & PF_KTHREAD)
- return to_kthread(task)->threadfn;
+ struct kthread *kthread = __to_kthread(task);
+ if (kthread)
+ return kthread->threadfn;
return NULL;
}
EXPORT_SYMBOL_GPL(kthread_func);
@@ -199,10 +219,11 @@ EXPORT_SYMBOL_GPL(kthread_data);
*/
void *kthread_probe_data(struct task_struct *task)
{
- struct kthread *kthread = to_kthread(task);
+ struct kthread *kthread = __to_kthread(task);
void *data = NULL;
- copy_from_kernel_nofault(&data, &kthread->data, sizeof(data));
+ if (kthread)
+ copy_from_kernel_nofault(&data, &kthread->data, sizeof(data));
return data;
}
@@ -514,9 +535,9 @@ void kthread_set_per_cpu(struct task_struct *k, int cpu)
set_bit(KTHREAD_IS_PER_CPU, &kthread->flags);
}
-bool kthread_is_per_cpu(struct task_struct *k)
+bool kthread_is_per_cpu(struct task_struct *p)
{
- struct kthread *kthread = to_kthread(k);
+ struct kthread *kthread = __to_kthread(p);
if (!kthread)
return false;
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 262b02d75007..bad97d35684d 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7569,7 +7569,7 @@ int can_migrate_task(struct task_struct *p, struct lb_env *env)
return 0;
/* Disregard pcpu kthreads; they are where they need to be. */
- if ((p->flags & PF_KTHREAD) && kthread_is_per_cpu(p))
+ if (kthread_is_per_cpu(p))
return 0;
if (!cpumask_test_cpu(env->dst_cpu, p->cpus_ptr)) {
--
2.29.2
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] kthread: Fix PF_KTHREAD vs to_kthread() race
2021-08-30 11:05 [PATCH] kthread: Fix PF_KTHREAD vs to_kthread() race Borislav Petkov
@ 2021-08-31 6:39 ` Patrick Schaaf
2021-09-01 9:44 ` Greg KH
1 sibling, 0 replies; 4+ messages in thread
From: Patrick Schaaf @ 2021-08-31 6:39 UTC (permalink / raw)
To: Borislav Petkov; +Cc: stable, bugzilla.kernel.org, anubis
On Mon, Aug 30, 2021 at 1:06 PM Borislav Petkov <bp@alien8.de> wrote:
>
> Hi stable folks,
>
> please queue for 5.10-stable.
>
> See https://bugzilla.kernel.org/show_bug.cgi?id=214159 for more info.
>
> ---
> Commit 3a7956e25e1d7b3c148569e78895e1f3178122a9 upstream.
...
Aha. Seconded, and please also consider for 5.4. This looks lke it
could fix the WARNING I reported, seen with 5.4.135, which Igor also
saw on 5.10.
best regards
Patrick
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] kthread: Fix PF_KTHREAD vs to_kthread() race
2021-08-30 11:05 [PATCH] kthread: Fix PF_KTHREAD vs to_kthread() race Borislav Petkov
2021-08-31 6:39 ` Patrick Schaaf
@ 2021-09-01 9:44 ` Greg KH
2021-09-01 11:45 ` Patrick Schaaf
1 sibling, 1 reply; 4+ messages in thread
From: Greg KH @ 2021-09-01 9:44 UTC (permalink / raw)
To: Borislav Petkov; +Cc: stable, bugzilla.kernel.org
On Mon, Aug 30, 2021 at 01:05:56PM +0200, Borislav Petkov wrote:
> Hi stable folks,
>
> please queue for 5.10-stable.
>
> See https://bugzilla.kernel.org/show_bug.cgi?id=214159 for more info.
Now queued up, thanks.
greg k-h
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] kthread: Fix PF_KTHREAD vs to_kthread() race
2021-09-01 9:44 ` Greg KH
@ 2021-09-01 11:45 ` Patrick Schaaf
0 siblings, 0 replies; 4+ messages in thread
From: Patrick Schaaf @ 2021-09-01 11:45 UTC (permalink / raw)
To: Greg KH; +Cc: Borislav Petkov, stable, bugzilla.kernel.org
On Wed, Sep 1, 2021 at 11:44 AM Greg KH <greg@kroah.com> wrote:
>
> On Mon, Aug 30, 2021 at 01:05:56PM +0200, Borislav Petkov wrote:
> >
> > please queue for 5.10-stable.
> >
> > See https://bugzilla.kernel.org/show_bug.cgi?id=214159 for more info.
>
> Now queued up, thanks.
I just booted a further of my prod servers with that applied to
5.10.61, patch needed a little mangling, attached below. Once more (as
with the 5.4 one), will report about stability in a few days,
initially looks fine.
best regards
Patrick
Tested-By: Patrick Schaaf <bof@bof.de>
diff -purN linux-5.10.61-orig/kernel/kthread.c linux-5.10.61-p/kernel/kthread.c
--- linux-5.10.61-orig/kernel/kthread.c 2021-08-26 14:51:21.000000000 +0200
+++ linux-5.10.61-p/kernel/kthread.c 2021-09-01 09:52:31.056738951 +0200
@@ -84,6 +84,25 @@ static inline struct kthread *to_kthread
return (__force void *)k->set_child_tid;
}
+/*
+ * Variant of to_kthread() that doesn't assume @p is a kthread.
+ *
+ * Per construction; when:
+ *
+ * (p->flags & PF_KTHREAD) && p->set_child_tid
+ *
+ * the task is both a kthread and struct kthread is persistent. However
+ * PF_KTHREAD on it's own is not, kernel_thread() can exec() (See umh.c and
+ * begin_new_exec()).
+ */
+static inline struct kthread *__to_kthread(struct task_struct *p)
+{
+ void *kthread = (__force void *)p->set_child_tid;
+ if (kthread && !(p->flags & PF_KTHREAD))
+ kthread = NULL;
+ return kthread;
+}
+
void free_kthread_struct(struct task_struct *k)
{
struct kthread *kthread;
@@ -168,8 +187,9 @@ EXPORT_SYMBOL_GPL(kthread_freezable_shou
*/
void *kthread_func(struct task_struct *task)
{
- if (task->flags & PF_KTHREAD)
- return to_kthread(task)->threadfn;
+ struct kthread *kthread = __to_kthread(task);
+ if (kthread)
+ return kthread->threadfn;
return NULL;
}
EXPORT_SYMBOL_GPL(kthread_func);
@@ -199,10 +219,11 @@ EXPORT_SYMBOL_GPL(kthread_data);
*/
void *kthread_probe_data(struct task_struct *task)
{
- struct kthread *kthread = to_kthread(task);
+ struct kthread *kthread = __to_kthread(task);
void *data = NULL;
- copy_from_kernel_nofault(&data, &kthread->data, sizeof(data));
+ if (kthread)
+ copy_from_kernel_nofault(&data, &kthread->data, sizeof(data));
return data;
}
@@ -514,9 +535,9 @@ void kthread_set_per_cpu(struct task_str
set_bit(KTHREAD_IS_PER_CPU, &kthread->flags);
}
-bool kthread_is_per_cpu(struct task_struct *k)
+bool kthread_is_per_cpu(struct task_struct *p)
{
- struct kthread *kthread = to_kthread(k);
+ struct kthread *kthread = __to_kthread(p);
if (!kthread)
return false;
diff -purN linux-5.10.61-orig/kernel/sched/fair.c
linux-5.10.61-p/kernel/sched/fair.c
--- linux-5.10.61-orig/kernel/sched/fair.c 2021-08-26
14:51:21.000000000 +0200
+++ linux-5.10.61-p/kernel/sched/fair.c 2021-09-01 09:48:06.860333848 +0200
@@ -7569,7 +7569,7 @@ int can_migrate_task(struct task_struct
return 0;
/* Disregard pcpu kthreads; they are where they need to be. */
- if ((p->flags & PF_KTHREAD) && kthread_is_per_cpu(p))
+ if (kthread_is_per_cpu(p))
return 0;
if (!cpumask_test_cpu(env->dst_cpu, p->cpus_ptr)) {
^ permalink raw reply [flat|nested] 4+ messages in thread
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2021-08-30 11:05 [PATCH] kthread: Fix PF_KTHREAD vs to_kthread() race Borislav Petkov
2021-08-31 6:39 ` Patrick Schaaf
2021-09-01 9:44 ` Greg KH
2021-09-01 11:45 ` Patrick Schaaf
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