boot: implement kernel EFI RNG seed protocol with proper hashing

[thirdparty/systemd.git] / src / core / efi-random.c

/* SPDX-License-Identifier: LGPL-2.1-or-later */

#include <fcntl.h>
#include <unistd.h>

#include "alloc-util.h"
#include "chattr-util.h"
#include "efi-random.h"
#include "efivars.h"
#include "fd-util.h"
#include "fs-util.h"
#include "random-util.h"
#include "strv.h"

void lock_down_efi_variables(void) {
        _cleanup_close_ int fd = -1;
        int r;

        fd = open(EFIVAR_PATH(EFI_LOADER_VARIABLE(LoaderSystemToken)), O_RDONLY|O_CLOEXEC);
        if (fd < 0) {
                if (errno != ENOENT)
                        log_warning_errno(errno, "Unable to open LoaderSystemToken EFI variable, ignoring: %m");
                return;
        }

        /* Paranoia: let's restrict access modes of these a bit, so that unprivileged users can't use them to
         * identify the system or gain too much insight into what we might have credited to the entropy
         * pool. */
        r = chattr_fd(fd, 0, FS_IMMUTABLE_FL, NULL);
        if (r < 0)
                log_warning_errno(r, "Failed to drop FS_IMMUTABLE_FL from LoaderSystemToken EFI variable, ignoring: %m");
        if (fchmod(fd, 0600) < 0)
                log_warning_errno(errno, "Failed to reduce access mode of LoaderSystemToken EFI variable, ignoring: %m");
}