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tpm2: write swtpm config files atomically via the state directory fd

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Open the swtpm state directory once and write the three config files
relative to that fd with WRITE_STRING_FILE_ATOMIC, rather than by path
with a plain truncating write. Writing atomically ensures a crash or a
concurrent reader never observes a half-written config file, and
operating through a single directory fd lets later steps reuse it.

Signed-off-by: Paul Meyer <katexochen0@gmail.com>
This commit is contained in:
Paul Meyer
2026-06-24 08:58:10 +02:00
parent 47b6a20621
commit abf96165a6
1 changed files with 13 additions and 9 deletions
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22
src/shared/swtpm-util.c
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@@ -135,6 +135,10 @@ int manufacture_swtpm(const char *state_dir, const char *secret) {
assert(state_dir);
_cleanup_close_ int state_dir_fd = xopenat(AT_FDCWD, state_dir, O_RDONLY|O_DIRECTORY|O_CLOEXEC);
if (state_dir_fd < 0)
return log_error_errno(state_dir_fd, "Failed to open TPM state directory '%s': %m", state_dir);
_cleanup_free_ char *swtpm_setup = NULL;
r = find_executable("swtpm_setup", &swtpm_setup);
if (r < 0)
@@ -151,9 +155,9 @@ int manufacture_swtpm(const char *state_dir, const char *secret) {
if (!localca_conf)
return log_oom();
r = write_string_filef(
localca_conf,
WRITE_STRING_FILE_CREATE|WRITE_STRING_FILE_TRUNCATE|WRITE_STRING_FILE_MKDIR_0755,
r = write_string_filef_at(
state_dir_fd, "swtpm-localca.conf",
WRITE_STRING_FILE_CREATE|WRITE_STRING_FILE_ATOMIC,
"statedir = %1$s\n"
"signingkey = %1$s/signing-private-key.pem\n"
"issuercert = %1$s/issuer-certificate.pem\n"
@@ -166,12 +170,12 @@ int manufacture_swtpm(const char *state_dir, const char *secret) {
if (!localca_options)
return log_oom();
r = write_string_file(
localca_options,
r = write_string_file_at(
state_dir_fd, "swtpm-localca.options",
"--platform-manufacturer systemd\n"
"--platform-version 2.1\n"
"--platform-model swtpm\n",
WRITE_STRING_FILE_CREATE|WRITE_STRING_FILE_TRUNCATE|WRITE_STRING_FILE_MKDIR_0755);
WRITE_STRING_FILE_CREATE|WRITE_STRING_FILE_ATOMIC);
if (r < 0)
return log_error_errno(r, "Failed to write swtpm-localca.options: %m");
@@ -184,9 +188,9 @@ int manufacture_swtpm(const char *state_dir, const char *secret) {
if (!setup_conf)
return log_oom();
r = write_string_filef(
setup_conf,
WRITE_STRING_FILE_CREATE|WRITE_STRING_FILE_TRUNCATE|WRITE_STRING_FILE_MKDIR_0755,
r = write_string_filef_at(
state_dir_fd, "swtpm_setup.conf",
WRITE_STRING_FILE_CREATE|WRITE_STRING_FILE_ATOMIC,
"create_certs_tool = %1$s\n"
"create_certs_tool_config = %2$s\n"
"create_certs_tool_options = %3$s\n",