[src/trunk]: src/sys/net Don't trigger BJ_ASSERT(false) on invalid BPF_Jxxx o...

[alnsn <alnsn%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/7c744ac437f8
branches:  trunk
changeset: 816858:7c744ac437f8
user:      alnsn <alnsn%NetBSD.org@localhost>
date:      Fri Jul 29 20:29:38 2016 +0000

description:
Don't trigger BJ_ASSERT(false) on invalid BPF_Jxxx opcode in jmp_to_op().

This change helps survive AFL fuzzing without calling bpf_validate() first.

Also change alu_to_op() function to have a similar interface.

diffstat:

 sys/net/bpfjit.c |  92 ++++++++++++++++++++++++++++++++-----------------------
 1 files changed, 53 insertions(+), 39 deletions(-)

diffs (174 lines):

diff -r db95fa8ee795 -r 7c744ac437f8 sys/net/bpfjit.c
--- a/sys/net/bpfjit.c  Fri Jul 29 20:27:37 2016 +0000
+++ b/sys/net/bpfjit.c  Fri Jul 29 20:29:38 2016 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: bpfjit.c,v 1.45 2016/05/29 17:20:22 alnsn Exp $        */
+/*     $NetBSD: bpfjit.c,v 1.46 2016/07/29 20:29:38 alnsn Exp $        */
 
 /*-
  * Copyright (c) 2011-2015 Alexander Nasonov.
@@ -31,9 +31,9 @@
 
 #include <sys/cdefs.h>
 #ifdef _KERNEL
-__KERNEL_RCSID(0, "$NetBSD: bpfjit.c,v 1.45 2016/05/29 17:20:22 alnsn Exp $");
+__KERNEL_RCSID(0, "$NetBSD: bpfjit.c,v 1.46 2016/07/29 20:29:38 alnsn Exp $");
 #else
-__RCSID("$NetBSD: bpfjit.c,v 1.45 2016/05/29 17:20:22 alnsn Exp $");
+__RCSID("$NetBSD: bpfjit.c,v 1.46 2016/07/29 20:29:38 alnsn Exp $");
 #endif
 
 #include <sys/types.h>
@@ -1594,10 +1594,9 @@
 /*
  * Convert BPF_ALU operations except BPF_NEG and BPF_DIV to sljit operation.
  */
-static int
-bpf_alu_to_sljit_op(const struct bpf_insn *pc)
+static bool
+alu_to_op(const struct bpf_insn *pc, int *res)
 {
-       const int bad = SLJIT_UNUSED;
        const uint32_t k = pc->k;
 
        /*
@@ -1605,49 +1604,64 @@
         * instruction so SLJIT_I32_OP doesn't have any overhead.
         */
        switch (BPF_OP(pc->code)) {
-       case BPF_ADD: return SLJIT_ADD;
-       case BPF_SUB: return SLJIT_SUB;
-       case BPF_MUL: return SLJIT_MUL|SLJIT_I32_OP;
-       case BPF_OR:  return SLJIT_OR;
-       case BPF_XOR: return SLJIT_XOR;
-       case BPF_AND: return SLJIT_AND;
-       case BPF_LSH: return (k > 31) ? bad : SLJIT_SHL;
-       case BPF_RSH: return (k > 31) ? bad : SLJIT_LSHR|SLJIT_I32_OP;
+       case BPF_ADD:
+               *res = SLJIT_ADD;
+               return true;
+       case BPF_SUB:
+               *res = SLJIT_SUB;
+               return true;
+       case BPF_MUL:
+               *res = SLJIT_MUL|SLJIT_I32_OP;
+               return true;
+       case BPF_OR:
+               *res = SLJIT_OR;
+               return true;
+       case BPF_XOR:
+               *res = SLJIT_XOR;
+               return true;
+       case BPF_AND:
+               *res = SLJIT_AND;
+               return true;
+       case BPF_LSH:
+               *res = SLJIT_SHL;
+               return k < 32;
+       case BPF_RSH:
+               *res = SLJIT_LSHR|SLJIT_I32_OP;
+               return k < 32;
        default:
-               return bad;
+               return false;
        }
 }
 
 /*
  * Convert BPF_JMP operations except BPF_JA to sljit condition.
  */
-static int
-bpf_jmp_to_sljit_cond(const struct bpf_insn *pc, bool negate)
+static bool
+jmp_to_cond(const struct bpf_insn *pc, bool negate, int *res)
 {
+
        /*
         * Note: all supported 64bit arches have 32bit comparison
         * instructions so SLJIT_I32_OP doesn't have any overhead.
         */
-       int rv = SLJIT_I32_OP;
+       *res = SLJIT_I32_OP;
 
        switch (BPF_OP(pc->code)) {
        case BPF_JGT:
-               rv |= negate ? SLJIT_LESS_EQUAL : SLJIT_GREATER;
-               break;
+               *res |= negate ? SLJIT_LESS_EQUAL : SLJIT_GREATER;
+               return true;
        case BPF_JGE:
-               rv |= negate ? SLJIT_LESS : SLJIT_GREATER_EQUAL;
-               break;
+               *res |= negate ? SLJIT_LESS : SLJIT_GREATER_EQUAL;
+               return true;
        case BPF_JEQ:
-               rv |= negate ? SLJIT_NOT_EQUAL : SLJIT_EQUAL;
-               break;
+               *res |= negate ? SLJIT_NOT_EQUAL : SLJIT_EQUAL;
+               return true;
        case BPF_JSET:
-               rv |= negate ? SLJIT_EQUAL : SLJIT_NOT_EQUAL;
-               break;
+               *res |= negate ? SLJIT_EQUAL : SLJIT_NOT_EQUAL;
+               return true;
        default:
-               BJ_ASSERT(false);
+               return false;
        }
-
-       return rv;
 }
 
 /*
@@ -1695,9 +1709,9 @@
        struct sljit_jump *to_mchain_jump;
 
        size_t i;
-       int status;
+       unsigned int rval, mode, src, op;
        int branching, negate;
-       unsigned int rval, mode, src, op;
+       int status, cond, op2;
        uint32_t jt, jf;
 
        bool unconditional_ret;
@@ -1935,10 +1949,9 @@
 
                        op = BPF_OP(pc->code);
                        if (op != BPF_DIV && op != BPF_MOD) {
-                               const int op2 = bpf_alu_to_sljit_op(pc);
+                               if (!alu_to_op(pc, &op2))
+                                       goto fail;
 
-                               if (op2 == SLJIT_UNUSED)
-                                       goto fail;
                                status = sljit_emit_op2(compiler,
                                    op2, BJ_AREG, 0, BJ_AREG, 0,
                                    kx_to_reg(pc), kx_to_reg_arg(pc));
@@ -2005,9 +2018,10 @@
 
                        if (branching) {
                                if (op != BPF_JSET) {
+                                       if (!jmp_to_cond(pc, negate, &cond))
+                                               goto fail;
                                        jump = sljit_emit_cmp(compiler,
-                                           bpf_jmp_to_sljit_cond(pc, negate),
-                                           BJ_AREG, 0,
+                                           cond, BJ_AREG, 0,
                                            kx_to_reg(pc), kx_to_reg_arg(pc));
                                } else {
                                        status = sljit_emit_op2(compiler,
@@ -2018,10 +2032,10 @@
                                        if (status != SLJIT_SUCCESS)
                                                goto fail;
 
+                                       if (!jmp_to_cond(pc, negate, &cond))
+                                               goto fail;
                                        jump = sljit_emit_cmp(compiler,
-                                           bpf_jmp_to_sljit_cond(pc, negate),
-                                           BJ_TMP1REG, 0,
-                                           SLJIT_IMM, 0);
+                                           cond, BJ_TMP1REG, 0, SLJIT_IMM, 0);
                                }
 
                                if (jump == NULL)