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-rw-r--r--wiretap/bpf-engine.c319
1 files changed, 319 insertions, 0 deletions
diff --git a/wiretap/bpf-engine.c b/wiretap/bpf-engine.c
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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 <netinet/in.h>
+#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;
+}
+
generated by cgit v1.2.3 (git 2.25.1) at 2024-07-08 22:44:33 +0000