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samples/seccomp/bpf-helper.c 2.34 KB
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8ac270d1e   Will Drewry   Documentation: pr... 
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  /*
   * Seccomp BPF helper functions
   *
   * Copyright (c) 2012 The Chromium OS Authors <chromium-os-dev@chromium.org>
   * Author: Will Drewry <wad@chromium.org>
   *
   * The code may be used by anyone for any purpose,
   * and can serve as a starting point for developing
   * applications using prctl(PR_ATTACH_SECCOMP_FILTER).
   */
  
  #include <stdio.h>
3a9af0bd3   Kees Cook   samples/seccomp: ... 
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  #include <stdlib.h>
8ac270d1e   Will Drewry   Documentation: pr... 
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  #include <string.h>
  
  #include "bpf-helper.h"
  
  int bpf_resolve_jumps(struct bpf_labels *labels,
  		      struct sock_filter *filter, size_t count)
  {
  	struct sock_filter *begin = filter;
  	__u8 insn = count - 1;
  
  	if (count < 1)
  		return -1;
  	/*
  	* Walk it once, backwards, to build the label table and do fixups.
  	* Since backward jumps are disallowed by BPF, this is easy.
  	*/
  	filter += insn;
  	for (; filter >= begin; --insn, --filter) {
  		if (filter->code != (BPF_JMP+BPF_JA))
  			continue;
  		switch ((filter->jt<<8)|filter->jf) {
  		case (JUMP_JT<<8)|JUMP_JF:
  			if (labels->labels[filter->k].location == 0xffffffff) {
  				fprintf(stderr, "Unresolved label: '%s'
  ",
  					labels->labels[filter->k].label);
  				return 1;
  			}
  			filter->k = labels->labels[filter->k].location -
  				    (insn + 1);
  			filter->jt = 0;
  			filter->jf = 0;
  			continue;
  		case (LABEL_JT<<8)|LABEL_JF:
  			if (labels->labels[filter->k].location != 0xffffffff) {
  				fprintf(stderr, "Duplicate label use: '%s'
  ",
  					labels->labels[filter->k].label);
  				return 1;
  			}
  			labels->labels[filter->k].location = insn;
  			filter->k = 0; /* fall through */
  			filter->jt = 0;
  			filter->jf = 0;
  			continue;
  		}
  	}
  	return 0;
  }
  
  /* Simple lookup table for labels. */
  __u32 seccomp_bpf_label(struct bpf_labels *labels, const char *label)
  {
  	struct __bpf_label *begin = labels->labels, *end;
  	int id;
3a9af0bd3   Kees Cook   samples/seccomp: ... 
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  	if (labels->count == BPF_LABELS_MAX) {
  		fprintf(stderr, "Too many labels
  ");
  		exit(1);
  	}
8ac270d1e   Will Drewry   Documentation: pr... 
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  	if (labels->count == 0) {
  		begin->label = label;
  		begin->location = 0xffffffff;
  		labels->count++;
  		return 0;
  	}
  	end = begin + labels->count;
  	for (id = 0; begin < end; ++begin, ++id) {
  		if (!strcmp(label, begin->label))
  			return id;
  	}
  	begin->label = label;
  	begin->location = 0xffffffff;
  	labels->count++;
  	return id;
  }
  
  void seccomp_bpf_print(struct sock_filter *filter, size_t count)
  {
  	struct sock_filter *end = filter + count;
  	for ( ; filter < end; ++filter)
  		printf("{ code=%u,jt=%u,jf=%u,k=%u },
  ",
  			filter->code, filter->jt, filter->jf, filter->k);
  }