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// Copyright (c) 2012-2016, Matt Godbolt
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//
// * Redistributions of source code must retain the above copyright notice,
// this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above copyright
// notice, this list of conditions and the following disclaimer in the
// documentation and/or other materials provided with the distribution.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
// POSSIBILITY OF SUCH DAMAGE.
#define _GNU_SOURCE
#include <dlfcn.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <errno.h>
#include <limits.h>
#include <stdlib.h>
#include <string.h>
#include <libgen.h>
#ifndef O_CREAT
#define O_CREAT 0100
#endif
// OS X et al doesn't have this. Rather than optionally replace it, I'd rather
// run using this substitute function all the time.
static const char *my_strchrnul(const char *s, int c) {
const char *ptr = strchr(s, c);
if (!ptr)
ptr = s + strlen(s);
return ptr;
}
static int allowed_match(const char* path, const char* okpath, const char *denypath) {
char resolvedBuf[PATH_MAX];
const char* resolved = path;
if (!strncmp(resolved, "/proc/self", 10)) {
// Leave references to /proc/self.* alone as its real path is different
// each time.
} else {
resolved = realpath(path, resolvedBuf);
if (resolved == NULL) {
return 0;
}
}
while (*denypath) {
const char* end = my_strchrnul(denypath, ':');
if (strncmp(denypath, resolved, end - denypath) == 0) goto deny;
denypath = end;
while (*denypath == ':') ++denypath;
}
while (*okpath) {
const char* end = my_strchrnul(okpath, ':');
if (strncmp(okpath, resolved, end - okpath) == 0) return 1;
okpath = end;
while (*okpath == ':') ++okpath;
}
deny:
fprintf(stderr, "Access to \"%s\" denied by gcc-explorer policy\n", path);
errno = EACCES;
return 0;
}
static int allowed_env(const char* pathname, const char* envvar) {
const char* okpath = getenv(envvar);
if (okpath == NULL) {
errno = EINVAL;
return 0;
}
const char* denypath = getenv("DENIED");
if (denypath == NULL) denypath = "";
// Check file name first
if (allowed_match(pathname, okpath, denypath)) return 1;
// Check directory name
char* dirpathbuf = strdup(pathname);
char* dirpath = dirname(dirpathbuf);
int dir_ok = allowed_match(dirpath, okpath, denypath);
free(dirpathbuf);
return dir_ok;
}
static int allowed(const char* pathname, int flags) {
if (flags & O_CREAT)
return allowed_env(pathname, "ALLOWED_FOR_CREATE");
else
return allowed_env(pathname, "ALLOWED_FOR_READ");
}
int open(const char *pathname, int flags, mode_t mode) {
static int (*real_open)(const char*, int, mode_t) = NULL;
if (!real_open) real_open = dlsym(RTLD_NEXT, "open");
if (!allowed(pathname, flags)) {
return -1;
}
return real_open(pathname, flags, mode);
}
int creat(const char *pathname, mode_t mode) {
static int (*real_creat)(const char*, mode_t) = NULL;
if (!real_creat) real_creat = dlsym(RTLD_NEXT, "creat");
if (!allowed(pathname, O_CREAT)) {
return -1;
}
return real_creat(pathname, mode);
}
FILE* fopen(const char* name, const char* mode) {
static FILE* (*real_fopen)(const char*, const char*) = NULL;
if (!real_fopen) real_fopen = dlsym(RTLD_NEXT, "fopen");
if (!allowed(name, (mode[0] == 'r') ? 0 : O_CREAT)) {
return NULL;
}
return real_fopen(name, mode);
}