From f5c16f29bf5e57ba4051fc7785ba7f035f798c71 Mon Sep 17 00:00:00 2001
From: Tejun Heo <tj@kernel.org>
Date: Mon, 19 May 2014 15:52:10 -0400
Subject: [PATCH] sysfs: make sure read buffer is zeroed

13c589d5b0ac ("sysfs: use seq_file when reading regular files")
switched sysfs from custom read implementation to seq_file to enable
later transition to kernfs.  After the change, the buffer passed to
->show() is acquired through seq_get_buf(); unfortunately, this
introduces a subtle behavior change.  Before the commit, the buffer
passed to ->show() was always zero as it was allocated using
get_zeroed_page().  Because seq_file doesn't clear buffers on
allocation and neither does seq_get_buf(), after the commit, depending
on the behavior of ->show(), we may end up exposing uninitialized data
to userland thus possibly altering userland visible behavior and
leaking information.

Fix it by explicitly clearing the buffer.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Ron <ron@debian.org>
Fixes: 13c589d5b0ac ("sysfs: use seq_file when reading regular files")
Cc: stable <stable@vger.kernel.org> # 3.13+
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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