* [PATCH 5.10 0/1] sched/fair: fix fault in reweight_entity()
@ 2022-08-19 7:11 Fedor Pchelkin
2022-08-19 7:11 ` [PATCH 5.10 1/1] sched/fair: Fix fault in reweight_entity Fedor Pchelkin
0 siblings, 1 reply; 3+ messages in thread
From: Fedor Pchelkin @ 2022-08-19 7:11 UTC (permalink / raw)
To: stable, Greg Kroah-Hartman
Cc: Fedor Pchelkin, Tadeusz Struk, Peter Zijlstra, Dietmar Eggemann,
linux-kernel, Alexey Khoroshilov, ldv-project
Syzkaller reports general protection fault at reweight_entity() in 5.10
stable releases. The problem has been fixed by the following patch which
can be applied with minor changes to the 5.10 branch.
Found by Linux Verification Center (linuxtesting.org) with Syzkaller.
^ permalink raw reply [flat|nested] 3+ messages in thread
* [PATCH 5.10 1/1] sched/fair: Fix fault in reweight_entity
2022-08-19 7:11 [PATCH 5.10 0/1] sched/fair: fix fault in reweight_entity() Fedor Pchelkin
@ 2022-08-19 7:11 ` Fedor Pchelkin
2022-08-19 11:25 ` Greg Kroah-Hartman
0 siblings, 1 reply; 3+ messages in thread
From: Fedor Pchelkin @ 2022-08-19 7:11 UTC (permalink / raw)
To: stable, Greg Kroah-Hartman
Cc: Fedor Pchelkin, Tadeusz Struk, Peter Zijlstra, Dietmar Eggemann,
linux-kernel, Alexey Khoroshilov, ldv-project,
syzbot+af7a719bc92395ee41b3
From: Tadeusz Struk <tadeusz.struk@linaro.org>
commit 13765de8148f71fa795e0a6607de37c49ea5915a upstream.
Syzbot found a GPF in reweight_entity. This has been bisected to
commit 4ef0c5c6b5ba ("kernel/sched: Fix sched_fork() access an invalid
sched_task_group")
There is a race between sched_post_fork() and setpriority(PRIO_PGRP)
within a thread group that causes a null-ptr-deref in
reweight_entity() in CFS. The scenario is that the main process spawns
number of new threads, which then call setpriority(PRIO_PGRP, 0, -20),
wait, and exit. For each of the new threads the copy_process() gets
invoked, which adds the new task_struct and calls sched_post_fork()
for it.
In the above scenario there is a possibility that
setpriority(PRIO_PGRP) and set_one_prio() will be called for a thread
in the group that is just being created by copy_process(), and for
which the sched_post_fork() has not been executed yet. This will
trigger a null pointer dereference in reweight_entity(), as it will
try to access the run queue pointer, which hasn't been set.
Before the mentioned change the cfs_rq pointer for the task has been
set in sched_fork(), which is called much earlier in copy_process(),
before the new task is added to the thread_group. Now it is done in
the sched_post_fork(), which is called after that. To fix the issue
the remove the update_load param from the update_load param() function
and call reweight_task() only if the task flag doesn't have the
TASK_NEW flag set.
Fixes: 4ef0c5c6b5ba ("kernel/sched: Fix sched_fork() access an invalid sched_task_group")
Reported-by: syzbot+af7a719bc92395ee41b3@syzkaller.appspotmail.com
Signed-off-by: Tadeusz Struk <tadeusz.struk@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20220203161846.1160750-1-tadeusz.struk@linaro.org
Signed-off-by: Fedor Pchelkin <pchelkin@ispras.ru>
---
5.10 adaptation: Replaced a task_struct field '__state' with 'state'
kernel/sched/core.c | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index e437d946b27b..86c5e08b393b 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -844,8 +844,9 @@ int tg_nop(struct task_group *tg, void *data)
}
#endif
-static void set_load_weight(struct task_struct *p, bool update_load)
+static void set_load_weight(struct task_struct *p)
{
+ bool update_load = !(READ_ONCE(p->state) & TASK_NEW);
int prio = p->static_prio - MAX_RT_PRIO;
struct load_weight *load = &p->se.load;
@@ -3262,7 +3263,7 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p)
p->static_prio = NICE_TO_PRIO(0);
p->prio = p->normal_prio = p->static_prio;
- set_load_weight(p, false);
+ set_load_weight(p);
/*
* We don't need the reset flag anymore after the fork. It has
@@ -5011,7 +5012,7 @@ void set_user_nice(struct task_struct *p, long nice)
put_prev_task(rq, p);
p->static_prio = NICE_TO_PRIO(nice);
- set_load_weight(p, true);
+ set_load_weight(p);
old_prio = p->prio;
p->prio = effective_prio(p);
@@ -5184,7 +5185,7 @@ static void __setscheduler_params(struct task_struct *p,
*/
p->rt_priority = attr->sched_priority;
p->normal_prio = normal_prio(p);
- set_load_weight(p, true);
+ set_load_weight(p);
}
/*
@@ -7189,7 +7190,7 @@ void __init sched_init(void)
atomic_set(&rq->nr_iowait, 0);
}
- set_load_weight(&init_task, false);
+ set_load_weight(&init_task);
/*
* The boot idle thread does lazy MMU switching as well:
--
2.25.1
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH 5.10 1/1] sched/fair: Fix fault in reweight_entity
2022-08-19 7:11 ` [PATCH 5.10 1/1] sched/fair: Fix fault in reweight_entity Fedor Pchelkin
@ 2022-08-19 11:25 ` Greg Kroah-Hartman
0 siblings, 0 replies; 3+ messages in thread
From: Greg Kroah-Hartman @ 2022-08-19 11:25 UTC (permalink / raw)
To: Fedor Pchelkin
Cc: stable, Tadeusz Struk, Peter Zijlstra, Dietmar Eggemann,
linux-kernel, Alexey Khoroshilov, ldv-project,
syzbot+af7a719bc92395ee41b3
On Fri, Aug 19, 2022 at 10:11:40AM +0300, Fedor Pchelkin wrote:
> From: Tadeusz Struk <tadeusz.struk@linaro.org>
>
> commit 13765de8148f71fa795e0a6607de37c49ea5915a upstream.
>
> Syzbot found a GPF in reweight_entity. This has been bisected to
> commit 4ef0c5c6b5ba ("kernel/sched: Fix sched_fork() access an invalid
> sched_task_group")
>
> There is a race between sched_post_fork() and setpriority(PRIO_PGRP)
> within a thread group that causes a null-ptr-deref in
> reweight_entity() in CFS. The scenario is that the main process spawns
> number of new threads, which then call setpriority(PRIO_PGRP, 0, -20),
> wait, and exit. For each of the new threads the copy_process() gets
> invoked, which adds the new task_struct and calls sched_post_fork()
> for it.
>
> In the above scenario there is a possibility that
> setpriority(PRIO_PGRP) and set_one_prio() will be called for a thread
> in the group that is just being created by copy_process(), and for
> which the sched_post_fork() has not been executed yet. This will
> trigger a null pointer dereference in reweight_entity(), as it will
> try to access the run queue pointer, which hasn't been set.
>
> Before the mentioned change the cfs_rq pointer for the task has been
> set in sched_fork(), which is called much earlier in copy_process(),
> before the new task is added to the thread_group. Now it is done in
> the sched_post_fork(), which is called after that. To fix the issue
> the remove the update_load param from the update_load param() function
> and call reweight_task() only if the task flag doesn't have the
> TASK_NEW flag set.
>
> Fixes: 4ef0c5c6b5ba ("kernel/sched: Fix sched_fork() access an invalid sched_task_group")
> Reported-by: syzbot+af7a719bc92395ee41b3@syzkaller.appspotmail.com
> Signed-off-by: Tadeusz Struk <tadeusz.struk@linaro.org>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
> Cc: stable@vger.kernel.org
> Link: https://lkml.kernel.org/r/20220203161846.1160750-1-tadeusz.struk@linaro.org
> Signed-off-by: Fedor Pchelkin <pchelkin@ispras.ru>
> ---
> 5.10 adaptation: Replaced a task_struct field '__state' with 'state'
Now queued up, thanks.
greg k-h
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