linux-kernel - [PATCH] sched: fix information leak in sys_sched

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Date:	Sun, 16 Feb 2014 22:24:17 +0100
From:	vegard.nossum@...cle.com
To:	Ingo Molnar <mingo@...nel.org>
Cc:	linux-kernel@...r.kernel.org,
	Vegard Nossum <vegard.nossum@...cle.com>,
	Dario Faggioli <raistlin@...ux.it>,
	Juri Lelli <juri.lelli@...il.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: [PATCH] sched: fix information leak in sys_sched_getattr()

From: Vegard Nossum <vegard.nossum@...cle.com>

We're copying the on-stack structure to userspace, but forgot to give
the right number of bytes to copy. This allows the calling process to
obtain up to PAGE_SIZE bytes from the stack (and possibly adjacent
kernel memory).

This fix copies only as much as we actually have on the stack
(attr->size defaults to the size of the struct) and leaves the rest of
the userspace-provided buffer untouched.

Found using kmemcheck + trinity.

Fixes: d50dde5a10f30 ("sched: Add new scheduler syscalls to support an extended scheduling parameters ABI")
Cc: Dario Faggioli <raistlin@...ux.it>
Cc: Juri Lelli <juri.lelli@...il.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Vegard Nossum <vegard.nossum@...cle.com>
---
 kernel/sched/core.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index b46131e..ac939c3 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3786,7 +3786,7 @@ static int sched_read_attr(struct sched_attr __user *uattr,
 		attr->size = usize;
 	}
 
-	ret = copy_to_user(uattr, attr, usize);
+	ret = copy_to_user(uattr, attr, attr->size);
 	if (ret)
 		return -EFAULT;
 
-- 
1.7.10.4

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