RtlValidRelativeSecurityDescriptor - NtDoc

Native API online documentation, based on the System Informer (formerly Process Hacker) phnt headers
#ifndef _NTRTL_H

_Check_return_
NTSYSAPI
BOOLEAN
NTAPI
RtlValidRelativeSecurityDescriptor(
    _In_reads_bytes_(SecurityDescriptorLength) PSECURITY_DESCRIPTOR SecurityDescriptorInput,
    _In_ ULONG SecurityDescriptorLength,
    _In_ SECURITY_INFORMATION RequiredInformation
    );

#endif

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This function is documented in Windows Driver Kit.