Simple audit library for intercepting/modifying library requests in glibc

crew-audit.c

#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <link.h>
#include <linux/limits.h>
#include <gnu/libc-version.h>

char *crew_prefix, crew_glibc_prefix[PATH_MAX], crew_libc_so_path[PATH_MAX];

unsigned int la_version(unsigned int interface_ver) {
  crew_prefix = getenv("CREW_PREFIX") ?: "/usr/local";

  snprintf(crew_glibc_prefix, PATH_MAX, "%s/opt/glibc-libs", crew_prefix);
  snprintf(crew_libc_so_path, PATH_MAX, "%s/libc.so.6", crew_glibc_prefix);

  fprintf(stderr, "crew-audit: Initialized on glibc %s with interface version %i\n", gnu_get_libc_version(), interface_ver);
  fprintf(stderr, "crew-audit: Chromebrew prefix: %s\n", crew_prefix);

  return LAV_CURRENT;
}

char *la_objsearch(const char *soname, uintptr_t *cookie, unsigned int flag) {
  char *new_path = malloc(PATH_MAX);

  // do not modify requests with absolute path
  if (soname[0] == '/') return soname;

  //printf("crew-audit: Library %s is being requested...\n", soname);

  if (strncmp(soname, "libC.so.6", strlen(soname)) == 0) {
    fprintf(stderr, "crew-audit: libC.so.6 being requested, replacing it with %s...\n", crew_libc_so_path);
    return crew_libc_so_path;
  }

  snprintf(new_path, PATH_MAX, "%s/opt/glibc-libs/%s", crew_prefix, soname);

  if (access(new_path, F_OK) == 0) {
    fprintf(stderr, "crew-audit: Library found in %s, using it instead...\n", new_path);
    return new_path;
  }

  return soname;
}