RtlFreeSid - NtDoc

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

NTSYSAPI
PVOID
NTAPI
RtlFreeSid(
    _In_ _Post_invalid_ PSID Sid
    );

#endif

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/*
 * RTL forward symbol typedefs
 *
 * This file is part of System Informer.
 */
#ifndef _NTRTL_FWD_H
// Note: ntdll symbols and exports define these forwarders:
// begin_forwarders
#ifndef PHNT_INLINE_FREE_FORWARDERS

//#define RtlFreeSid(Sid) RtlFreeHeap(RtlProcessHeap(), 0, (Sid))
FORCEINLINE
PVOID
NTAPI
RtlFreeSid(
    _In_ _Post_invalid_ PSID Sid
    )
{
    RtlFreeHeap(RtlProcessHeap(), 0, Sid);
    return NULL;
}

#endif
// end_forwarders
#endif

View code on GitHub

This function is documented in Windows Driver Kit.