Commit e491fe6e authored Nov 18, 2022 by Tadeusz Struk Committed by Zheng Zengkai Nov 18, 2022

sched/fair: Fix fault in reweight_entity

stable inclusion
from stable-v5.10.137
commit 8f317cd888059c59e2fa924bf4b0957cfa53f78e
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I60PLB

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8f317cd888059c59e2fa924bf4b0957cfa53f78e



--------------------------------

commit 13765de8 upstream.

Syzbot found a GPF in reweight_entity. This has been bisected to
commit 4ef0c5c6 ("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: 4ef0c5c6 ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>
Reviewed-by: Wei Li <liwei391@huawei.com>

parent 66d7622b

kernel/sched/core.c

+6 −5

Original line number	Diff line number	Diff line
		@@ -1189,8 +1189,9 @@ 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;

		@@ -3653,7 +3654,7 @@ 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
		@@ -6068,7 +6069,7 @@ 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);

		@@ -6241,7 +6242,7 @@ 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);
		}

		/*
		@@ -8292,7 +8293,7 @@ void __init sched_init(void)
		#endif
		}

		set_load_weight(&init_task, false);
		set_load_weight(&init_task);

		/*
		* The boot idle thread does lazy MMU switching as well: