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/*
* Sandboxing example
*
* Uses custom memory allocation functions which keep track of total amount
* of memory allocated, imposing a maximum total allocation size.
*/
#include <stdio.h>
#include <stdlib.h>
#include "duktape.h"
/*
* Memory allocator which backs to standard library memory functions but
* keeps a small header to track current allocation size.
*
* Many other sandbox allocation models are useful, e.g. preallocated pools.
*/
typedef struct {
/* The double value in the union is there to ensure alignment is
* good for IEEE doubles too. In many 32-bit environments 4 bytes
* would be sufficiently aligned and the double value is unnecessary.
*/
union {
size_t sz;
double d;
} u;
} alloc_hdr;
static size_t total_allocated = 0;
static size_t max_allocated = 256 * 1024; /* 256kB sandbox */
static void sandbox_dump_memstate(void) {
#if 0
fprintf(stderr, "Total allocated: %ld\n", (long) total_allocated);
fflush(stderr);
#endif
}
static void *sandbox_alloc(void *udata, duk_size_t size) {
alloc_hdr *hdr;
(void) udata; /* Suppress warning. */
if (size == 0) {
return NULL;
}
if (total_allocated + size > max_allocated) {
fprintf(stderr, "Sandbox maximum allocation size reached, %ld requested in sandbox_alloc\n",
(long) size);
fflush(stderr);
return NULL;
}
hdr = (alloc_hdr *) malloc(size + sizeof(alloc_hdr));
if (!hdr) {
return NULL;
}
hdr->u.sz = size;
total_allocated += size;
sandbox_dump_memstate();
return (void *) (hdr + 1);
}
static void *sandbox_realloc(void *udata, void *ptr, duk_size_t size) {
alloc_hdr *hdr;
size_t old_size;
void *t;
(void) udata; /* Suppress warning. */
/* Handle the ptr-NULL vs. size-zero cases explicitly to minimize
* platform assumptions. You can get away with much less in specific
* well-behaving environments.
*/
if (ptr) {
hdr = (alloc_hdr *) (((char *) ptr) - sizeof(alloc_hdr));
old_size = hdr->u.sz;
if (size == 0) {
total_allocated -= old_size;
free((void *) hdr);
sandbox_dump_memstate();
return NULL;
} else {
if (total_allocated - old_size + size > max_allocated) {
fprintf(stderr, "Sandbox maximum allocation size reached, %ld requested in sandbox_realloc\n",
(long) size);
fflush(stderr);
return NULL;
}
t = realloc((void *) hdr, size + sizeof(alloc_hdr));
if (!t) {
return NULL;
}
hdr = (alloc_hdr *) t;
total_allocated -= old_size;
total_allocated += size;
hdr->u.sz = size;
sandbox_dump_memstate();
return (void *) (hdr + 1);
}
} else {
if (size == 0) {
return NULL;
} else {
if (total_allocated + size > max_allocated) {
fprintf(stderr, "Sandbox maximum allocation size reached, %ld requested in sandbox_realloc\n",
(long) size);
fflush(stderr);
return NULL;
}
hdr = (alloc_hdr *) malloc(size + sizeof(alloc_hdr));
if (!hdr) {
return NULL;
}
hdr->u.sz = size;
total_allocated += size;
sandbox_dump_memstate();
return (void *) (hdr + 1);
}
}
}
static void sandbox_free(void *udata, void *ptr) {
alloc_hdr *hdr;
(void) udata; /* Suppress warning. */
if (!ptr) {
return;
}
hdr = (alloc_hdr *) (((char *) ptr) - sizeof(alloc_hdr));
total_allocated -= hdr->u.sz;
free((void *) hdr);
sandbox_dump_memstate();
}
/*
* Sandbox setup and test
*/
static duk_ret_t do_sandbox_test(duk_context *ctx) {
FILE *f;
char buf[4096];
size_t ret;
const char *globobj;
/*
* Setup sandbox
*/
globobj =
"({\n"
" print: print,\n"
" Math: {\n"
" max: Math.max\n"
" }\n"
"})\n";
#if 1
fprintf(stderr, "Sandbox global object:\n----------------\n%s----------------\n", globobj);
fflush(stderr);
#endif
duk_eval_string(ctx, globobj);
duk_set_global_object(ctx);
/*
* Execute code from specified file
*/
f = fopen(duk_require_string(ctx, -1), "rb");
if (!f) {
duk_error(ctx, DUK_ERR_ERROR, "failed to open file");
}
for (;;) {
if (ferror(f)) {
fclose(f);
duk_error(ctx, DUK_ERR_ERROR, "ferror when reading file");
}
if (feof(f)) {
break;
}
ret = fread(buf, 1, sizeof(buf), f);
if (ret == 0) {
break;
}
duk_push_lstring(ctx, (const char *) buf, ret);
}
duk_concat(ctx, duk_get_top(ctx) - 1); /* -1 for filename */
/* -> [ ... filename source ] */
duk_insert(ctx, -2);
/* -> [ ... source filename ] */
duk_compile(ctx, 0 /*flags*/); /* Compile as program */
duk_call(ctx, 0 /*nargs*/);
return 0;
}
/*
* Main
*/
static void sandbox_fatal(duk_context *ctx, duk_errcode_t code, const char *msg) {
(void) ctx; /* Suppress warning. */
fprintf(stderr, "FATAL %ld: %s\n", (long) code, (msg ? msg : "no message"));
fflush(stderr);
exit(1); /* must not return */
}
int main(int argc, char *argv[]) {
duk_context *ctx;
duk_int_t rc;
if (argc < 2) {
fprintf(stderr, "Usage: sandbox <test.js>\n");
fflush(stderr);
exit(1);
}
ctx = duk_create_heap(sandbox_alloc,
sandbox_realloc,
sandbox_free,
NULL,
sandbox_fatal);
duk_push_string(ctx, argv[1]);
rc = duk_safe_call(ctx, do_sandbox_test, 1 /*nargs*/, 1 /*nrets*/);
if (rc) {
fprintf(stderr, "ERROR: %s\n", duk_safe_to_string(ctx, -1));
fflush(stderr);
}
duk_destroy_heap(ctx);
/* Should be zero. */
fprintf(stderr, "Final allocation: %ld\n", (long) total_allocated);
fflush(stderr);
return 1;
}
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