ima: Extend permissions to the ima securityfs entries

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I49KW1


CVE: NA

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Add "others" permissions to the namespaced ima securityfs entries. It
is necessary so that the root in the user namespace that is the parent
of the given ima namespace has access to the ima related data.

Loosened DAC restrictrions are compensated by an extra check for
SYS_ADMIN capabilities in the ima code. The access is given
only to the namespaced data, e.g. root user in the new ima namespace
will see measurement list entries collected for that namespace and not
for the other existing namespaces. The only exception is made for the
admin in the initial user namespace, who has access to all the data.

Signed-off-by: Krzysztof Struczynski <krzysztof.struczynski@huawei.com>
Reviewed-by: Zhang Tianxing <zhangtianxing3@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>