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|
/* bpf-engine.c
* ------------
* The BPF engine used for offline ("display") filters in wiretap.
* The code is taken from the Linux Socket Filter, and only slightly
* modified for use in wiretap.
*
* Gilbert Ramirez <gram@verdict.uthscsa.edu>
*/
/*
* Linux Socket Filter - Kernel level socket filtering
*
* Author:
* Jay Schulist <Jay.Schulist@spacs.k12.wi.us>
*
* Based on the design of:
* - The Berkeley Packet Filter
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version
* 2 of the License, or (at your option) any later version.
*/
#include <glib.h>
#include "wtap.h"
#include "bpf-engine.h"
/*
* Decode and apply filter instructions to the skb->data.
* Return length to keep, 0 for none. skb is the data we are
* filtering, filter is the array of filter instructions, and
* len is the number of filter blocks in the array.
*/
int bpf_run_filter(unsigned char *data, int len, struct bpf_instruction *filter, int flen)
{
struct bpf_instruction *fentry; /* We walk down these */
guint32 A = 0; /* Accumulator */
guint32 X = 0; /* Index Register */
guint32 mem[BPF_MEMWORDS]; /* Scratch Memory Store */
int k;
int pc;
int *t;
/*
* Process array of filter instructions.
*/
for(pc = 0; pc < flen; pc++)
{
fentry = &filter[pc];
if(fentry->code & BPF_X)
t=&X;
else
t=&fentry->k;
switch(fentry->code)
{
case BPF_ALU|BPF_ADD|BPF_X:
case BPF_ALU|BPF_ADD|BPF_K:
A += *t;
continue;
case BPF_ALU|BPF_SUB|BPF_X:
case BPF_ALU|BPF_SUB|BPF_K:
A -= *t;
continue;
case BPF_ALU|BPF_MUL|BPF_X:
case BPF_ALU|BPF_MUL|BPF_K:
A *= *t;
continue;
case BPF_ALU|BPF_DIV|BPF_X:
case BPF_ALU|BPF_DIV|BPF_K:
if(*t == 0)
return (0);
A /= *t;
continue;
case BPF_ALU|BPF_AND|BPF_X:
case BPF_ALU|BPF_AND|BPF_K:
A &= *t;
continue;
case BPF_ALU|BPF_OR|BPF_X:
case BPF_ALU|BPF_OR|BPF_K:
A |= *t;
continue;
case BPF_ALU|BPF_LSH|BPF_X:
case BPF_ALU|BPF_LSH|BPF_K:
A <<= *t;
continue;
case BPF_ALU|BPF_RSH|BPF_X:
case BPF_ALU|BPF_RSH|BPF_K:
A >>= *t;
continue;
case BPF_ALU|BPF_NEG:
A = -A;
continue;
case BPF_JMP|BPF_JA:
pc += fentry->k;
continue;
case BPF_JMP|BPF_JGT|BPF_K:
pc += (A > fentry->k) ? fentry->jt : fentry->jf;
continue;
case BPF_JMP|BPF_JGE|BPF_K:
pc += (A >= fentry->k) ? fentry->jt : fentry->jf;
continue;
case BPF_JMP|BPF_JEQ|BPF_K:
pc += (A == fentry->k) ? fentry->jt : fentry->jf;
continue;
case BPF_JMP|BPF_JSET|BPF_K:
pc += (A & fentry->k) ? fentry->jt : fentry->jf;
continue;
case BPF_JMP|BPF_JGT|BPF_X:
pc += (A > X) ? fentry->jt : fentry->jf;
continue;
case BPF_JMP|BPF_JGE|BPF_X:
pc += (A >= X) ? fentry->jt : fentry->jf;
continue;
case BPF_JMP|BPF_JEQ|BPF_X:
pc += (A == X) ? fentry->jt : fentry->jf;
continue;
case BPF_JMP|BPF_JSET|BPF_X:
pc += (A & X) ? fentry->jt : fentry->jf;
continue;
case BPF_LD|BPF_W|BPF_ABS:
k = fentry->k;
if(k + sizeof(long) > len)
return (0);
A = pntohl(&data[k]);
continue;
case BPF_LD|BPF_H|BPF_ABS:
k = fentry->k;
if(k + sizeof(short) > len)
return (0);
A = pntohs(&data[k]);
continue;
case BPF_LD|BPF_B|BPF_ABS:
k = fentry->k;
if(k >= len)
return (0);
A = data[k];
continue;
case BPF_LD|BPF_W|BPF_LEN:
A = len;
continue;
case BPF_LDX|BPF_W|BPF_LEN:
X = len;
continue;
case BPF_LD|BPF_W|BPF_IND:
k = X + fentry->k;
if(k + sizeof(guint32) > len)
return (0);
A = pntohl(&data[k]);
continue;
case BPF_LD|BPF_H|BPF_IND:
k = X + fentry->k;
if(k + sizeof(guint16) > len)
return (0);
A = pntohs(&data[k]);
continue;
case BPF_LD|BPF_B|BPF_IND:
k = X + fentry->k;
if(k >= len)
return (0);
A = data[k];
continue;
case BPF_LDX|BPF_B|BPF_MSH:
/*
* Hack for BPF to handle TOS etc
*/
k = fentry->k;
if(k >= len)
return (0);
X = (data[fentry->k] & 0xf) << 2;
continue;
case BPF_LD|BPF_IMM:
A = fentry->k;
continue;
case BPF_LDX|BPF_IMM:
X = fentry->k;
continue;
case BPF_LD|BPF_MEM:
A = mem[fentry->k];
continue;
case BPF_LDX|BPF_MEM:
X = mem[fentry->k];
continue;
case BPF_MISC|BPF_TAX:
X = A;
continue;
case BPF_MISC|BPF_TXA:
A = X;
continue;
case BPF_RET|BPF_K:
return ((unsigned int)fentry->k);
case BPF_RET|BPF_A:
return ((unsigned int)A);
case BPF_ST:
mem[fentry->k] = A;
continue;
case BPF_STX:
mem[fentry->k] = X;
continue;
default:
/* Invalid instruction counts as RET */
return (0);
}
}
g_error("Filter ruleset ran off the end.\n");
return (0);
}
/*
* Check the user's filter code. If we let some ugly
* filter code slip through kaboom!
*/
int bpf_chk_filter(struct bpf_instruction *filter, int flen)
{
struct bpf_instruction *ftest;
int pc;
/*
* Check the filter code now.
*/
for(pc = 0; pc < flen; pc++)
{
/*
* All jumps are forward as they are not signed
*/
ftest = &filter[pc];
if(BPF_CLASS(ftest->code) == BPF_JMP)
{
/*
* But they mustn't jump off the end.
*/
if(BPF_OP(ftest->code) == BPF_JA)
{
if(pc + ftest->k + 1>= (unsigned)flen)
return (-1);
}
else
{
/*
* For conditionals both must be safe
*/
if(pc + ftest->jt +1 >= flen || pc + ftest->jf +1 >= flen)
return (-1);
}
}
/*
* Check that memory operations use valid addresses.
*/
if(ftest->k <0 || ftest->k >= BPF_MEMWORDS)
{
/*
* But it might not be a memory operation...
*/
if (BPF_CLASS(ftest->code) == BPF_ST)
return -1;
if((BPF_CLASS(ftest->code) == BPF_LD) &&
(BPF_MODE(ftest->code) == BPF_MEM))
return (-1);
}
}
/*
* The program must end with a return. We don't care where they
* jumped within the script (its always forwards) but in the
* end they _will_ hit this.
*/
return (BPF_CLASS(filter[flen - 1].code) == BPF_RET)?0:-1;
}
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