Get POSIX File ACLs on Linux

Get_File_Acls.c

/*
 * Copyright 2015 Simon Schmidt
 *
 * Usage of the works is permitted provided that this instrument is
 * retained with the works, so that any entity that uses the works
 * is notified of this instrument.
 * DISCLAIMER: THE WORKS ARE WITHOUT WARRANTY.
 */
#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/xattr.h>

/* All values are Little Endian */
/* On Big Endian archs, the program needs modifications */

typedef struct{
	uint16_t tag;
	uint16_t perm;
	uint32_t id;
} pacl_ent;

/* pacl_ent.tag values */
/*
const uint16_t PAET_USER_OWNER = 0x0001;
const uint16_t PAET_USER = 0x0002;
const uint16_t PAET_GROUP_OWNER = 0x0004;
const uint16_t PAET_GROUP = 0x0008;
const uint16_t PAET_MASK = 0x0010;
const uint16_t PAET_OTHERS = 0x0020;
*/

#define PAET_USER_OWNER  0x0001
#define PAET_USER        0x0002
#define PAET_GROUP_OWNER 0x0004
#define PAET_GROUP       0x0008
#define PAET_MASK        0x0010
#define PAET_OTHERS      0x0020

typedef struct{
	uint32_t ver;
	pacl_ent e[0];
} pacl_head;
/* pacl_head.ver = 2 */

const uint32_t NOID = 0xffffffffU;

char permb[10];
char buf[1<<16];

inline char *decodeperm(int perm) {
	char *c = permb;
	if(perm&4)*(c++)='r';
	if(perm&2)*(c++)='w';
	if(perm&1)*(c++)='x';
	*c = 0;
	return permb;
}

int main(int argc,const char **argv){
	int i,j=0;
	for(i=0;i<(1<<16);++i)buf[i]=0;
	if(argc<2)return 1;
	int s = lgetxattr(argv[1],"system.posix_acl_access",buf,1<<16);
	if(s>(1<<16))s=1<<16;
	char *b = buf;
	pacl_ent *e = (pacl_ent*)(b+s);
	if(0>s)return 1;
	pacl_head *ph = (pacl_head*)b;
	pacl_ent *pe = ph->e;
	if(ph->ver!=2)return 1;
	printf("ACL\n");
	for(;;pe++){
		if(pe>=e)break;
		switch(pe->tag) {
			case PAET_USER_OWNER:
				printf(" usr.OWNER.%s\n",decodeperm(pe->perm)); break;
			case PAET_USER:
				printf(" usr.%d.%s\n",(int)(pe->id),decodeperm(pe->perm)); break;
			case PAET_GROUP_OWNER:
				printf(" rol.OWNER.%s\n",decodeperm(pe->perm)); break;
			case PAET_GROUP:
				printf(" rol.%d.%s\n",(int)(pe->id),decodeperm(pe->perm)); break;
		}
		//printf("%x; %x; %x\n",(unsigned)(pe->tag),(unsigned)(pe->perm),(unsigned)(pe->id));
	}
	printf(";;\n");
	printf("\n");
	return 0;
}