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From: Kangjie Lu <>
Cc:, Ingo Molnar <>,
	Peter Zijlstra <>,
Subject: [PATCH v2] sched: fix a potential double-fetch bug in sched_copy_attr
Date: Wed,  9 Jan 2019 01:45:24 -0600
Message-ID: <> (raw)
In-Reply-To: <>

"uattr->size" is copied in from user space and checked. However, it is
copied in again after the security check. A malicious user may race to
change it. The fix sets uattr->size to be the checked size.

Signed-off-by: Kangjie Lu <>
 kernel/sched/core.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 6fedf3a98581..e868cc25ac2a 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4499,6 +4499,9 @@ static int sched_copy_attr(struct sched_attr __user *uattr, struct sched_attr *a
 	if (ret)
 		return -EFAULT;
+	/* In case attr->size was changed in the user space */
+	attr->size = size;
 	 * XXX: Do we want to be lenient like existing syscalls; or do we want
 	 * to be strict and return an error on out-of-bounds values?

  reply index

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-12-25 22:16 [PATCH] " Kangjie Lu
2019-01-07 17:11 ` Peter Zijlstra
2019-01-09  7:45   ` Kangjie Lu [this message]
2019-01-21 11:32     ` [tip:sched/core] sched/core: Fix a potential double-fetch bug in sched_copy_attr() tip-bot for Kangjie Lu
2019-01-27 11:04       ` Thomas Gleixner
2019-01-27 11:28         ` Ingo Molnar
2019-01-28  7:58         ` Peter Zijlstra
2019-01-28 13:15           ` Thomas Gleixner
2019-03-10 10:09             ` Thomas Gleixner

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