linux-kernel - [tip: sched/urgent] sched/fair: Fix fault in reweight

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <164424192533.16921.7865952180431807276.tip-bot2@tip-bot2>
Date:   Mon, 07 Feb 2022 13:52:05 -0000
From:   "tip-bot2 for Tadeusz Struk" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     syzbot+af7a719bc92395ee41b3@...kaller.appspotmail.com,
        Tadeusz Struk <tadeusz.struk@...aro.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        stable@...r.kernel.org, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: sched/urgent] sched/fair: Fix fault in reweight_entity

The following commit has been merged into the sched/urgent branch of tip:

Commit-ID:     13765de8148f71fa795e0a6607de37c49ea5915a
Gitweb:        https://git.kernel.org/tip/13765de8148f71fa795e0a6607de37c49ea5915a
Author:        Tadeusz Struk <tadeusz.struk@...aro.org>
AuthorDate:    Thu, 03 Feb 2022 08:18:46 -08:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Sun, 06 Feb 2022 22:37:26 +01:00

sched/fair: Fix fault in reweight_entity

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@...kaller.appspotmail.com
Signed-off-by: Tadeusz Struk <tadeusz.struk@...aro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@....com>
Cc: stable@...r.kernel.org
Link: https://lkml.kernel.org/r/20220203161846.1160750-1-tadeusz.struk@linaro.org
---
 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 848eaa0..fcf0c18 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1214,8 +1214,9 @@ 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;

@@ -4406,7 +4407,7 @@ 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
@@ -6921,7 +6922,7 @@ 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);

@@ -7212,7 +7213,7 @@ 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);
 }

 /*
@@ -9445,7 +9446,7 @@ 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: