ima: Add a reader counter to the integrity inode data

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


CVE: NA

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To detect ToMToU violations reader counter of the given inode is
checked. This is not enough, because the reader may exist in a
different ima namespace. Per inode reader counter tracks readers in all
ima namespaces, whereas the per namespace counter is necessary to avoid
false positives.

Add a new reader counter to the integrity inode cache entry.

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