22 #include <sys/prctl.h>    23 #include <sys/syscall.h>    24 #include <linux/capability.h>    25 #include <linux/securebits.h>    27 #if !defined(SECBIT_KEEP_CAPS) && defined(SECURE_KEEP_CAPS)    28 #define SECBIT_KEEP_CAPS (issecure_mask(SECURE_KEEP_CAPS))    30 #if !defined(SECBIT_KEEP_CAPS_LOCKED) && defined(SECURE_KEEP_CAPS_LOCKED)    31 #define SECBIT_KEEP_CAPS_LOCKED (issecure_mask(SECURE_KEEP_CAPS_LOCKED))    33 #if !defined(SECBIT_NO_SETUID_FIXUP) && defined(SECURE_NO_SETUID_FIXUP)    34 #define SECBIT_NO_SETUID_FIXUP (issecure_mask(SECURE_NO_SETUID_FIXUP))    36 #if !defined(SECBIT_NO_SETUID_FIXUP_LOCKED) && defined(SECURE_NO_SETUID_FIXUP_LOCKED)    37 #define SECBIT_NO_SETUID_FIXUP_LOCKED (issecure_mask(SECURE_NO_SETUID_FIXUP_LOCKED))    39 #if !defined(SECBIT_NOROOT) && defined(SECURE_NOROOT)    40 #define SECBIT_NOROOT (issecure_mask(SECURE_NOROOT))    42 #if !defined(SECBIT_NOROOT_LOCKED) && defined(SECURE_NOROOT_LOCKED)    43 #define SECBIT_NOROOT_LOCKED (issecure_mask(SECURE_NOROOT_LOCKED))    49 static char *progname;
    51 static char *xstrdup(
const char *s)
    55                 fprintf(stderr, 
"%s: failed to allocate memory\n", progname);
    61 static void *xrealloc(
void *oldptr, 
size_t size)
    63         void *ptr = realloc(oldptr, size);
    65                 fprintf(stderr, 
"%s: failed to allocate memory\n", progname);
    71 static void add_arg(
char **cmdp, 
const char *opt)
    73         size_t optlen = strlen(opt);
    74         size_t cmdlen = *cmdp ? strlen(*cmdp) : 0;
    75         if (optlen >= (SIZE_MAX - cmdlen - 4)/4) {
    76                 fprintf(stderr, 
"%s: argument too long\n", progname);
    79         char *cmd = xrealloc(*cmdp, cmdlen + optlen * 4 + 4);
   100 static char *add_option(
const char *opt, 
char *options)
   102         int oldlen = options ? strlen(options) : 0;
   104         options = xrealloc(options, oldlen + 1 + strlen(opt) + 1);
   106                 strcpy(options, opt);
   108                 strcat(options, 
",");
   109                 strcat(options, opt);
   114 static int prepare_fuse_fd(
const char *mountpoint, 
const char* subtype,
   119         int subtype_len = strlen(subtype) + 9;
   120         char* options_copy = xrealloc(NULL, subtype_len);
   122         snprintf(options_copy, subtype_len, 
"subtype=%s", subtype);
   123         options_copy = add_option(options, options_copy);
   129         flags = fcntl(fuse_fd, F_GETFD);
   130         if (flags == -1 || fcntl(fuse_fd, F_SETFD, flags & ~FD_CLOEXEC) == 1) {
   131                 fprintf(stderr, 
"%s: Failed to clear CLOEXEC: %s\n",
   132                         progname, strerror(errno));
   140 static uint64_t get_capabilities(
void)
   146         struct __user_cap_header_struct header = {
   147                 .version = _LINUX_CAPABILITY_VERSION_3,
   150         struct __user_cap_data_struct data[2];
   151         memset(data, 0, 
sizeof(data));
   152         if (syscall(SYS_capget, &header, data) == -1) {
   153                 fprintf(stderr, 
"%s: Failed to get capabilities: %s\n",
   154                         progname, strerror(errno));
   158         return data[0].effective | ((uint64_t) data[1].effective << 32);
   161 static void set_capabilities(uint64_t caps)
   167         struct __user_cap_header_struct header = {
   168                 .version = _LINUX_CAPABILITY_VERSION_3,
   171         struct __user_cap_data_struct data[2];
   172         memset(data, 0, 
sizeof(data));
   173         data[0].effective = data[0].permitted = caps;
   174         data[1].effective = data[1].permitted = caps >> 32;
   175         if (syscall(SYS_capset, &header, data) == -1) {
   176                 fprintf(stderr, 
"%s: Failed to set capabilities: %s\n",
   177                         progname, strerror(errno));
   182 static void drop_and_lock_capabilities(
void)
   185         if (prctl(PR_SET_SECUREBITS,
   186                   SECBIT_KEEP_CAPS_LOCKED |
   187                   SECBIT_NO_SETUID_FIXUP |
   188                   SECBIT_NO_SETUID_FIXUP_LOCKED |
   190                   SECBIT_NOROOT_LOCKED) == -1) {
   191                 fprintf(stderr, 
"%s: Failed to set securebits %s\n",
   192                         progname, strerror(errno));
   198         for (cap = 0; ; cap++) {
   199                 int cap_status = prctl(PR_CAPBSET_READ, cap);
   200                 if (cap_status == 0) {
   203                 if (cap_status == -1 && errno == EINVAL) {
   207                 if (cap_status != 1) {
   209                                 "%s: Failed to get capability %u: %s\n",
   210                                 progname, cap, strerror(errno));
   213                 if (prctl(PR_CAPBSET_DROP, cap) == -1) {
   215                                 "%s: Failed to drop capability %u: %s\n",
   216                                 progname, cap, strerror(errno));
   224         if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) == -1) {
   225                 fprintf(stderr, 
"%s: Failed to set no_new_privs: %s\n",
   226                         progname, strerror(errno));
   232 int main(
int argc, 
char *argv[])
   236         const char *mountpoint;
   238         char *options = NULL;
   239         char *command = NULL;
   240         char *setuid_name = NULL;
   244         int pass_fuse_fd = 0;
   245         int drop_privileges = 0;
   248         basename = strrchr(argv[0], 
'/');
   254         if (strncmp(basename, 
"mount.fuse.", 11) == 0)
   255                 type = basename + 11;
   256         if (strncmp(basename, 
"mount.fuseblk.", 14) == 0)
   257                 type = basename + 14;
   259         if (type && !type[0])
   264                         "usage: %s %s destination [-t type] [-o opt[,opts...]]\n",
   265                         progname, type ? 
"source" : 
"type#[source]");
   273         mountpoint = argv[2];
   275         for (i = 3; i < argc; i++) {
   276                 if (strcmp(argv[i], 
"-v") == 0) {
   278                 } 
else if (strcmp(argv[i], 
"-t") == 0) {
   283                                         "%s: missing argument to option '-t'\n",
   288                         if (strncmp(type, 
"fuse.", 5) == 0)
   290                         else if (strncmp(type, 
"fuseblk.", 8) == 0)
   295                                         "%s: empty type given as argument to option '-t'\n",
   299                 } 
else  if (strcmp(argv[i], 
"-o") == 0) {
   306                         opts = xstrdup(argv[i]);
   307                         opt = strtok(opts, 
",");
   311                                 const char *ignore_opts[] = { 
"",
   320                                 if (strncmp(opt, 
"setuid=", 7) == 0) {
   321                                         setuid_name = xstrdup(opt + 7);
   323                                 } 
else if (strcmp(opt,
   324                                                   "drop_privileges") == 0) {
   329                                 for (j = 0; ignore_opts[j]; j++)
   330                                         if (strcmp(opt, ignore_opts[j]) == 0)
   334                                         if (strcmp(opt, 
"nodev") == 0)
   336                                         else if (strcmp(opt, 
"nosuid") == 0)
   339                                         options = add_option(opt, options);
   341                                 opt = strtok(NULL, 
",");
   346         if (drop_privileges) {
   347                 uint64_t required_caps = CAP_TO_MASK(CAP_SETPCAP) |
   348                                 CAP_TO_MASK(CAP_SYS_ADMIN);
   349                 if ((get_capabilities() & required_caps) != required_caps) {
   350                         fprintf(stderr, 
"%s: drop_privileges was requested, which launches the FUSE file system fully unprivileged. In order to do so %s must be run with privileges, please invoke with CAP_SYS_ADMIN and CAP_SETPCAP (e.g. as root).\n",
   357                 options = add_option(
"dev", options);
   359                 options = add_option(
"suid", options);
   363                         type = xstrdup(source);
   364                         source = strchr(type, 
'#');
   368                                 fprintf(stderr, 
"%s: empty filesystem type\n",
   373                         fprintf(stderr, 
"%s: empty source\n", progname);
   378         if (setuid_name && setuid_name[0]) {
   380                 if (drop_privileges) {
   389                         if (prctl(PR_SET_SECUREBITS,
   391                                   SECBIT_NO_SETUID_FIXUP) == -1) {
   393                                         "%s: Failed to set securebits %s\n",
   394                                         progname, strerror(errno));
   400                 struct passwd *pwd = getpwnam(setuid_name);
   401                 if (setgid(pwd->pw_gid) == -1 || setuid(pwd->pw_uid) == -1) {
   402                         fprintf(stderr, 
"%s: Failed to setuid to %s: %s\n",
   403                                 progname, setuid_name, strerror(errno));
   406         } 
else if (!getenv(
"HOME")) {
   408                 setenv(
"HOME", 
"/root", 0);
   412                 int fuse_fd = prepare_fuse_fd(mountpoint, type, options);
   413                 char *dev_fd_mountpoint = xrealloc(NULL, 20);
   414                 snprintf(dev_fd_mountpoint, 20, 
"/dev/fd/%u", fuse_fd);
   415                 mountpoint = dev_fd_mountpoint;
   419         if (drop_privileges) {
   420                 drop_and_lock_capabilities();
   423         add_arg(&command, type);
   425                 add_arg(&command, source);
   426         add_arg(&command, mountpoint);
   428                 add_arg(&command, 
"-o");
   429                 add_arg(&command, options);
   432         execl(
"/bin/sh", 
"/bin/sh", 
"-c", command, NULL);
   433         fprintf(stderr, 
"%s: failed to execute /bin/sh: %s\n", progname,
 int fuse_open_channel(const char *mountpoint, const char *options)