static int contains_ordinary_appliance (guestfs_h *g, const char *path, void *data);
static int contains_supermin_appliance (guestfs_h *g, const char *path, void *data);
static char *calculate_supermin_checksum (guestfs_h *g, const char *supermin_path);
-static int check_for_cached_appliance (guestfs_h *g, const char *supermin_path, const char *checksum, char **kernel, char **initrd, char **appliance);
-static int build_supermin_appliance (guestfs_h *g, const char *supermin_path, const char *checksum, char **kernel, char **initrd, char **appliance);
+static int check_for_cached_appliance (guestfs_h *g, const char *supermin_path, const char *checksum, uid_t uid, char **kernel, char **initrd, char **appliance);
+static int build_supermin_appliance (guestfs_h *g, const char *supermin_path, const char *checksum, uid_t uid, char **kernel, char **initrd, char **appliance);
+static int hard_link_to_cached_appliance (guestfs_h *g, const char *cachedir, char **kernel, char **initrd, char **appliance);
static int run_supermin_helper (guestfs_h *g, const char *supermin_path, const char *cachedir, size_t cdlen);
/* Locate or build the appliance.
* (1) Look for the first element of g->path which contains a
* supermin appliance skeleton. If no element has this, skip
* straight to step (5).
+ *
* (2) Calculate the checksum of this supermin appliance.
- * (3) Check whether $TMPDIR/$checksum/ directory exists, contains
- * a cached appliance, and passes basic security checks. If so,
- * return this appliance.
- * (4) Try to build the supermin appliance into $TMPDIR/$checksum/.
- * If this is successful, return it.
+ *
+ * (3) Check whether a cached appliance with the checksum calculated
+ * in (2) exists and passes basic security checks. If so, return
+ * this appliance.
+ *
+ * (4) Try to build the supermin appliance. If this is successful,
+ * return it.
+ *
* (5) Check each element of g->path, looking for an ordinary appliance.
* If one is found, return it.
+ *
+ * The supermin appliance cache directory lives in
+ * $TMPDIR/.guestfs-$UID/ and consists of four files:
+ *
+ * $TMPDIR/.guestfs-$UID/checksum - the checksum
+ * $TMPDIR/.guestfs-$UID/kernel - symlink to the kernel
+ * $TMPDIR/.guestfs-$UID/initrd - the febootstrap initrd
+ * $TMPDIR/.guestfs-$UID/root - the appliance
+ *
+ * Since multiple instances of libguestfs with the same UID may be
+ * racing to create an appliance, we need to be careful when building
+ * and using the appliance.
+ *
+ * If a cached appliance with checksum exists (step (2) above) then we
+ * make a hard link to it with our current PID, so that we have a copy
+ * even if the appliance is replaced by another process building an
+ * appliance afterwards:
+ *
+ * $TMPDIR/.guestfs-$UID/kernel.$PID
+ * $TMPDIR/.guestfs-$UID/initrd.$PID
+ * $TMPDIR/.guestfs-$UID/root.$PID
+ *
+ * A lock is taken on "checksum" while we perform the link.
+ *
+ * Linked files are deleted by a garbage collection sweep which can be
+ * initiated by any libguestfs process with the same UID when the
+ * corresponding PID no longer exists. (This is safe: the parent is
+ * always around in guestfs_launch() while qemu is starting up, and
+ * after that qemu will either have finished with the files or be
+ * holding them open, so we can unlink them).
+ *
+ * When building a new appliance (step (3)), it is built into randomly
+ * named temporary files in the $TMPDIR. Then a lock is acquired on
+ * $TMPDIR/.guestfs-$UID/checksum (this file being created if
+ * necessary), the files are renamed into their final location, and
+ * the lock is released.
*/
int
guestfs___build_appliance (guestfs_h *g,
char **kernel, char **initrd, char **appliance)
{
int r;
+ uid_t uid = geteuid ();
/* Step (1). */
char *supermin_path;
char *checksum = calculate_supermin_checksum (g, supermin_path);
if (checksum) {
/* Step (3): cached appliance exists? */
- r = check_for_cached_appliance (g, supermin_path, checksum,
+ r = check_for_cached_appliance (g, supermin_path, checksum, uid,
kernel, initrd, appliance);
if (r != 0) {
free (supermin_path);
}
/* Step (4): build supermin appliance. */
- r = build_supermin_appliance (g, supermin_path, checksum,
+ r = build_supermin_appliance (g, supermin_path, checksum, uid,
kernel, initrd, appliance);
free (supermin_path);
free (checksum);
return safe_strndup (g, checksum, len);
}
-/* Check for cached appliance in $TMPDIR/$checksum. Check it exists
- * and passes some basic security checks.
- *
- * Returns:
- * 1 = exists, and passes
- * 0 = does not exist
- * -1 = error which should abort the whole launch process
- */
static int
-security_check_cache_file (guestfs_h *g, const char *filename,
- const struct stat *statbuf)
+process_exists (int pid)
{
- uid_t uid = geteuid ();
+ if (kill (pid, 0) == 0)
+ return 1;
- if (statbuf->st_uid != uid) {
- error (g, ("libguestfs cached appliance %s is not owned by UID %d\n"),
- filename, uid);
- return -1;
- }
+ if (errno == ESRCH)
+ return 0;
- if ((statbuf->st_mode & 0022) != 0) {
- error (g, ("libguestfs cached appliance %s is writable by group or other (mode %o)\n"),
- filename, statbuf->st_mode);
- return -1;
+ return -1;
+}
+
+/* Garbage collect appliance hard links. Files that match
+ * (kernel|initrd|root).$PID where the corresponding PID doesn't exist
+ * are deleted. Note that errors in this function don't matter.
+ * There may also be other libguestfs processes racing to do the same
+ * thing here.
+ */
+static void
+garbage_collect_appliances (const char *cachedir)
+{
+ DIR *dir;
+ struct dirent *d;
+ int pid;
+
+ dir = opendir (cachedir);
+ if (dir == NULL)
+ return;
+
+ while ((d = readdir (dir)) != NULL) {
+ if (sscanf (d->d_name, "kernel.%d", &pid) == 1 &&
+ process_exists (pid) == 0)
+ unlinkat (dirfd (dir), d->d_name, 0);
+ else if (sscanf (d->d_name, "initrd.%d", &pid) == 1 &&
+ process_exists (pid) == 0)
+ unlinkat (dirfd (dir), d->d_name, 0);
+ else if (sscanf (d->d_name, "root.%d", &pid) == 1 &&
+ process_exists (pid) == 0)
+ unlinkat (dirfd (dir), d->d_name, 0);
}
- return 0;
+ closedir (dir);
}
static int
check_for_cached_appliance (guestfs_h *g,
const char *supermin_path, const char *checksum,
+ uid_t uid,
char **kernel, char **initrd, char **appliance)
{
const char *tmpdir = guestfs_tmpdir ();
- size_t len = strlen (tmpdir) + strlen (checksum) + 10;
+ /* len must be longer than the length of any pathname we can
+ * generate in this function.
+ */
+ size_t len = strlen (tmpdir) + 128;
char cachedir[len];
- snprintf (cachedir, len, "%s/guestfs.%s", tmpdir, checksum);
+ snprintf (cachedir, len, "%s/.guestfs-%d", tmpdir, uid);
+ char filename[len];
+ snprintf (filename, len, "%s/checksum", cachedir);
- /* Touch the directory to prevent it being deleting in a rare race
- * between us doing the checks and a tmp cleaner running. Note this
- * doesn't create the directory, and we ignore any error.
- */
+ (void) mkdir (cachedir, 0755);
(void) utime (cachedir, NULL);
/* See if the cache directory exists and passes some simple checks
- * to make sure it has not been tampered with. Note that geteuid()
- * forms a part of the checksum.
+ * to make sure it has not been tampered with.
*/
struct stat statbuf;
if (lstat (cachedir, &statbuf) == -1)
return 0;
-
- if (security_check_cache_file (g, cachedir, &statbuf) == -1)
+ if (statbuf.st_uid != uid) {
+ error (g, _("security: cached appliance %s is not owned by UID %d\n"),
+ filename, uid);
+ return -1;
+ }
+ if (!S_ISDIR (statbuf.st_mode)) {
+ error (g, _("security: cached appliance %s is not a directory (mode %o)\n"),
+ filename, statbuf.st_mode);
+ return -1;
+ }
+ if ((statbuf.st_mode & 0022) != 0) {
+ error (g, _("security: cached appliance %s is writable by group or other (mode %o)\n"),
+ cachedir, statbuf.st_mode);
return -1;
-
- int ret;
-
- *kernel = safe_malloc (g, len + 8 /* / + "kernel" + \0 */);
- *initrd = safe_malloc (g, len + 8 /* / + "initrd" + \0 */);
- *appliance = safe_malloc (g, len + 6 /* / + "root" + \0 */);
- sprintf (*kernel, "%s/kernel", cachedir);
- sprintf (*initrd, "%s/initrd", cachedir);
- sprintf (*appliance, "%s/root", cachedir);
-
- /* Touch the files to prevent them being deleted, and to bring the
- * cache up to date. Note this doesn't create the files.
- */
- (void) utime (*kernel, NULL);
-
- /* NB. *kernel is a symlink, so we want to check the kernel, not the
- * link (stat, not lstat). We don't do a security check on the
- * kernel since it's always under /boot.
- */
- if (stat (*kernel, &statbuf) == -1) {
- ret = 0;
- goto error;
}
- (void) utime (*initrd, NULL);
+ garbage_collect_appliances (cachedir);
- if (lstat (*initrd, &statbuf) == -1) {
- ret = 0;
- goto error;
+ /* Try to open and acquire a lock on the checksum file. */
+ int fd = open (filename, O_RDONLY);
+ if (fd == -1)
+ return 0;
+ (void) futimens (fd, NULL);
+ struct flock fl;
+ fl.l_type = F_RDLCK;
+ fl.l_whence = SEEK_SET;
+ fl.l_start = 0;
+ fl.l_len = 1;
+ again:
+ if (fcntl (fd, F_SETLKW, &fl) == -1) {
+ if (errno == EINTR)
+ goto again;
+ perrorf (g, "fcntl: F_SETLKW: %s", filename);
+ close (fd);
+ return -1;
}
- if (security_check_cache_file (g, *initrd, &statbuf) == -1) {
- ret = -1;
- goto error;
+ /* Read the checksum file. */
+ size_t clen = strlen (checksum);
+ char checksum_on_disk[clen];
+ ssize_t rr = read (fd, checksum_on_disk, clen);
+ if (rr == -1) {
+ perrorf (g, "read: %s", filename);
+ close (fd);
+ return -1;
+ }
+ if ((size_t) rr != clen) {
+ close (fd);
+ return 0;
}
- (void) utime (*appliance, NULL);
+ if (memcmp (checksum, checksum_on_disk, clen) != 0) {
+ close (fd);
+ return 0;
+ }
- if (lstat (*appliance, &statbuf) == -1) {
- ret = 0;
- goto error;
+ /* At this point, cachedir exists, and checksum matches, and we have
+ * a read lock on the checksum file. Make hard links to the files.
+ */
+ if (hard_link_to_cached_appliance (g, cachedir,
+ kernel, initrd, appliance) == -1) {
+ close (fd);
+ return -1;
}
- if (security_check_cache_file (g, *appliance, &statbuf) == -1) {
- ret = -1;
- goto error;
+ /* Releases the lock on checksum. */
+ if (close (fd) == -1) {
+ perrorf (g, "close");
+ return -1;
}
/* Exists! */
return 1;
-
- error:
- free (*kernel);
- free (*initrd);
- free (*appliance);
- return ret;
}
-/* Build supermin appliance from supermin_path to $TMPDIR/$checksum.
+/* Build supermin appliance from supermin_path to $TMPDIR/.guestfs-$UID.
*
* Returns:
* 0 = built
static int
build_supermin_appliance (guestfs_h *g,
const char *supermin_path, const char *checksum,
+ uid_t uid,
char **kernel, char **initrd, char **appliance)
{
if (g->verbose)
const char *tmpdir = guestfs_tmpdir ();
- size_t tmpcdlen = strlen (tmpdir) + 16;
- char tmpcd[tmpcdlen];
- snprintf (tmpcd, tmpcdlen, "%s/guestfs.XXXXXX", tmpdir);
+ /* len must be longer than the length of any pathname we can
+ * generate in this function.
+ */
+ size_t len = strlen (tmpdir) + 128;
+
+ /* Build the appliance into a temporary directory. */
+ char tmpcd[len];
+ snprintf (tmpcd, len, "%s/guestfs.XXXXXX", tmpdir);
- if (NULL == mkdtemp (tmpcd)) {
- error (g, _("failed to create temporary cache directory: %m"));
+ if (mkdtemp (tmpcd) == NULL) {
+ perrorf (g, "mkdtemp");
return -1;
}
if (g->verbose)
guestfs___print_timestamped_message (g, "run febootstrap-supermin-helper");
- int r = run_supermin_helper (g, supermin_path, tmpcd, tmpcdlen);
+ int r = run_supermin_helper (g, supermin_path, tmpcd, len);
if (r == -1)
return -1;
if (g->verbose)
guestfs___print_timestamped_message (g, "finished building supermin appliance");
- size_t cdlen = strlen (tmpdir) + strlen (checksum) + 10;
- char cachedir[cdlen];
- snprintf (cachedir, cdlen, "%s/guestfs.%s", tmpdir, checksum);
-
- /* Make the temporary directory world readable */
- if (chmod (tmpcd, 0755) == -1) {
- error (g, "chmod %s: %m", tmpcd);
- }
-
- /* Try to rename the temporary directory to its non-temporary name */
- if (rename (tmpcd, cachedir) == -1) {
- /* If the cache directory now exists, we may have been racing with another
- * libguestfs process. Check the new directory and use it if it's valid. */
- if (errno == ENOTEMPTY || errno == EEXIST) {
- /* Appliance cache consists of 2 files and a symlink in the cache
- * directory. Delete them first. */
- DIR *dir = opendir (tmpcd);
- if (dir == NULL) {
- error (g, "opendir %s: %m", tmpcd);
- return -1;
- }
+ char cachedir[len];
+ snprintf (cachedir, len, "%s/.guestfs-%d", tmpdir, uid);
+ char filename[len];
+ char filename2[len];
+ snprintf (filename, len, "%s/checksum", cachedir);
- int fd = dirfd (dir);
- if (fd == -1) {
- error (g, "dirfd: %m");
- closedir (dir);
- return -1;
- }
+ /* Open and acquire write lock on checksum file. The file might
+ * not exist, in which case we want to create it.
+ */
+ int fd = open (filename, O_WRONLY|O_CREAT, 0755);
+ if (fd == -1) {
+ perrorf (g, "open: %s", filename);
+ return -1;
+ }
+ struct flock fl;
+ fl.l_type = F_WRLCK;
+ fl.l_whence = SEEK_SET;
+ fl.l_start = 0;
+ fl.l_len = 1;
+ again:
+ if (fcntl (fd, F_SETLKW, &fl) == -1) {
+ if (errno == EINTR)
+ goto again;
+ perrorf (g, "fcntl: F_SETLKW: %s", filename);
+ close (fd);
+ return -1;
+ }
- struct dirent *dirent;
- for (;;) {
- errno = 0;
- dirent = readdir (dir);
-
- if (dirent == NULL) {
- break;
- }
-
- /* Check that dirent is a file so we don't try to delete . and .. */
- struct stat st;
- if (fstatat (fd, dirent->d_name, &st, AT_SYMLINK_NOFOLLOW) == -1) {
- error (g, "fstatat %s: %m", dirent->d_name);
- return -1;
- }
-
- if (!S_ISDIR(st.st_mode)) {
- if (unlinkat (fd, dirent->d_name, 0) == -1) {
- error (g, "unlinkat %s: %m", dirent->d_name);
- closedir (dir);
- return -1;
- }
- }
- }
+ /* At this point we have acquired a write lock on the checksum
+ * file so we go ahead and replace it with the new checksum, and
+ * rename in appliance files into this directory.
+ */
+ size_t clen = strlen (checksum);
+ if (ftruncate (fd, clen) == -1) {
+ perrorf (g, "ftruncate: %s", filename);
+ close (fd);
+ return -1;
+ }
- if (errno != 0) {
- error (g, "readdir %s: %m", tmpcd);
- closedir (dir);
- return -1;
- }
+ ssize_t rr = write (fd, checksum, clen);
+ if (rr == -1) {
+ perrorf (g, "write: %s", filename);
+ close (fd);
+ return -1;
+ }
+ if ((size_t) rr != clen) {
+ error (g, "partial write: %s", filename);
+ close (fd);
+ return -1;
+ }
- closedir (dir);
+ snprintf (filename, len, "%s/kernel", tmpcd);
+ snprintf (filename2, len, "%s/kernel", cachedir);
+ unlink (filename2);
+ if (rename (filename, filename2) == -1) {
+ perrorf (g, "rename: %s %s", filename, filename2);
+ close (fd);
+ return -1;
+ }
- /* Delete the temporary cache directory itself. */
- if (rmdir (tmpcd) == -1) {
- error (g, "rmdir %s: %m", tmpcd);
- return -1;
- }
+ snprintf (filename, len, "%s/initrd", tmpcd);
+ snprintf (filename2, len, "%s/initrd", cachedir);
+ unlink (filename2);
+ if (rename (filename, filename2) == -1) {
+ perrorf (g, "rename: %s %s", filename, filename2);
+ close (fd);
+ return -1;
+ }
- /* Check the new cache directory, and return it if valid */
- return check_for_cached_appliance (g, supermin_path, checksum,
- kernel, initrd, appliance);
- }
+ snprintf (filename, len, "%s/root", tmpcd);
+ snprintf (filename2, len, "%s/root", cachedir);
+ unlink (filename2);
+ if (rename (filename, filename2) == -1) {
+ perrorf (g, "rename: %s %s", filename, filename2);
+ close (fd);
+ return -1;
+ }
- else {
- error (g, _("error renaming temporary cache directory: %m"));
- return -1;
- }
+ rmdir (tmpcd);
+
+ /* Now finish off by linking to the cached appliance and returning it. */
+ if (hard_link_to_cached_appliance (g, cachedir,
+ kernel, initrd, appliance) == -1) {
+ close (fd);
+ return -1;
+ }
+
+ /* Releases the lock on checksum. */
+ if (close (fd) == -1) {
+ perrorf (g, "close");
+ return -1;
}
- *kernel = safe_malloc (g, cdlen + 8 /* / + "kernel" + \0 */);
- *initrd = safe_malloc (g, cdlen + 8 /* / + "initrd" + \0 */);
- *appliance = safe_malloc (g, cdlen + 6 /* / + "root" + \0 */);
- sprintf (*kernel, "%s/kernel", cachedir);
- sprintf (*initrd, "%s/initrd", cachedir);
- sprintf (*appliance, "%s/root", cachedir);
+ return 0;
+}
+
+/* NB: lock on checksum file must be held when this is called. */
+static int
+hard_link_to_cached_appliance (guestfs_h *g,
+ const char *cachedir,
+ char **kernel, char **initrd, char **appliance)
+{
+ pid_t pid = getpid ();
+ size_t len = strlen (cachedir) + 32;
+
+ *kernel = safe_malloc (g, len);
+ *initrd = safe_malloc (g, len);
+ *appliance = safe_malloc (g, len);
+ snprintf (*kernel, len, "%s/kernel.%d", cachedir, pid);
+ snprintf (*initrd, len, "%s/initrd.%d", cachedir, pid);
+ snprintf (*appliance, len, "%s/root.%d", cachedir, pid);
+
+ char filename[len];
+ snprintf (filename, len, "%s/kernel", cachedir);
+ (void) unlink (*kernel);
+ if (link (filename, *kernel) == -1) {
+ perrorf (g, "link: %s %s", filename, *kernel);
+ goto error;
+ }
+ snprintf (filename, len, "%s/initrd", cachedir);
+ (void) unlink (*initrd);
+ if (link (filename, *initrd) == -1) {
+ perrorf (g, "link: %s %s", filename, *initrd);
+ goto error;
+ }
+ snprintf (filename, len, "%s/root", cachedir);
+ (void) unlink (*appliance);
+ if (link (filename, *appliance) == -1) {
+ perrorf (g, "link: %s %s", filename, *appliance);
+ goto error;
+ }
return 0;
+
+ error:
+ free (*kernel);
+ free (*initrd);
+ free (*appliance);
+ return -1;
}
/* Run febootstrap-supermin-helper and tell it to generate the
git.annexia.org / libguestfs.git / commitdiff