linux-kernel - [PATCH] sched/core: fix double fetch in sched_copy

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Date:   Mon, 15 Jul 2019 20:33:42 -0700
From:   JingYi Hou <houjingyi647@...il.com>
To:     mingo@...hat.com, peterz@...radead.org
Cc:     linux-kernel@...r.kernel.org
Subject: [PATCH] sched/core: fix double fetch in sched_copy_attr()

In sched_copy_attr(), attr->size was fetched twice in get_user()
and copy_from_user().

If change it between two fetches may cause security problems
or unexpected behaivor.

We can apply the same pattern used in perf_copy_attr(). That
is, use value fetched first time to overwrite it after second fetch.

Signed-off-by: JingYi Hou <houjingyi647@...il.com>
---
 kernel/sched/core.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 2b037f195473..60088b907ef4 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4945,6 +4945,8 @@ static int sched_copy_attr(struct sched_attr __user *uattr, struct sched_attr *a
 	ret = copy_from_user(attr, uattr, size);
 	if (ret)
 		return -EFAULT;
+
+	attr->size = size;

 	if ((attr->sched_flags & SCHED_FLAG_UTIL_CLAMP) &&
 	    size < SCHED_ATTR_SIZE_VER1)
--
2.20.1