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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-07 15:35:18 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-07 15:35:18 +0000 |
commit | b750101eb236130cf056c675997decbac904cc49 (patch) | |
tree | a5df1a06754bdd014cb975c051c83b01c9a97532 /src/core/efi-random.c | |
parent | Initial commit. (diff) | |
download | systemd-upstream.tar.xz systemd-upstream.zip |
Adding upstream version 252.22.upstream/252.22upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to '')
-rw-r--r-- | src/core/efi-random.c | 90 |
1 files changed, 90 insertions, 0 deletions
diff --git a/src/core/efi-random.c b/src/core/efi-random.c new file mode 100644 index 0000000..4086b12 --- /dev/null +++ b/src/core/efi-random.c @@ -0,0 +1,90 @@ +/* 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" + +/* If a random seed was passed by the boot loader in the LoaderRandomSeed EFI variable, let's credit it to + * the kernel's random pool, but only once per boot. If this is run very early during initialization we can + * instantly boot up with a filled random pool. + * + * This makes no judgement on the entropy passed, it's the job of the boot loader to only pass us a seed that + * is suitably validated. */ + +static void lock_down_efi_variables(void) { + int r; + + /* 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. */ + FOREACH_STRING(path, + EFIVAR_PATH(EFI_LOADER_VARIABLE(LoaderRandomSeed)), + EFIVAR_PATH(EFI_LOADER_VARIABLE(LoaderSystemToken))) { + + r = chattr_path(path, 0, FS_IMMUTABLE_FL, NULL); + if (r == -ENOENT) + continue; + if (r < 0) + log_warning_errno(r, "Failed to drop FS_IMMUTABLE_FL from %s, ignoring: %m", path); + + if (chmod(path, 0600) < 0) + log_warning_errno(errno, "Failed to reduce access mode of %s, ignoring: %m", path); + } +} + +int efi_take_random_seed(void) { + _cleanup_free_ void *value = NULL; + size_t size; + int r; + + /* Paranoia comes first. */ + lock_down_efi_variables(); + + if (access("/run/systemd/efi-random-seed-taken", F_OK) < 0) { + if (errno != ENOENT) { + log_warning_errno(errno, "Failed to determine whether we already used the random seed token, not using it."); + return 0; + } + + /* ENOENT means we haven't used it yet. */ + } else { + log_debug("EFI random seed already used, not using again."); + return 0; + } + + r = efi_get_variable(EFI_LOADER_VARIABLE(LoaderRandomSeed), NULL, &value, &size); + if (r == -EOPNOTSUPP) { + log_debug_errno(r, "System lacks EFI support, not initializing random seed from EFI variable."); + return 0; + } + if (r == -ENOENT) { + log_debug_errno(r, "Boot loader did not pass LoaderRandomSeed EFI variable, not crediting any entropy."); + return 0; + } + if (r < 0) + return log_warning_errno(r, "Failed to read LoaderRandomSeed EFI variable, ignoring: %m"); + + if (size == 0) + return log_warning_errno(SYNTHETIC_ERRNO(EINVAL), "Random seed passed from boot loader has zero size? Ignoring."); + + /* Before we use the seed, let's mark it as used, so that we never credit it twice. Also, it's a nice + * way to let users known that we successfully acquired entropy from the boot loader. */ + r = touch("/run/systemd/efi-random-seed-taken"); + if (r < 0) + return log_warning_errno(r, "Unable to mark EFI random seed as used, not using it: %m"); + + r = random_write_entropy(-1, value, size, true); + if (r < 0) + return log_warning_errno(errno, "Failed to credit entropy, ignoring: %m"); + + log_info("Successfully credited entropy passed from boot loader."); + return 1; +} |