firmware: qemu_fw_cfg: fix sysfs information leak

stable inclusion
from stable-v5.10.93
commit ff9588cf1592c4c8c83ff7ad30cc355a54da344f
bugzilla: 186204 https://gitee.com/openeuler/kernel/issues/I5311N

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ff9588cf1592c4c8c83ff7ad30cc355a54da344f



--------------------------------

commit 1b656e9a upstream.

Make sure to always NUL-terminate file names retrieved from the firmware
to avoid accessing data beyond the entry slab buffer and exposing it
through sysfs in case the firmware data is corrupt.

Fixes: 75f3e8e4 ("firmware: introduce sysfs driver for QEMU's fw_cfg device")
Cc: stable@vger.kernel.org      # 4.6
Cc: Gabriel Somlo <somlo@cmu.edu>
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20211201132528.30025-4-johan@kernel.org


Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Chen Jun <chenjun102@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>
Acked-by: Xie XiuQi <xiexiuqi@huawei.com>