initrd-cpio: add a variant that returns the credentials cpio in memory

systemd-firstboot wants to wrap the archive into a PE section rather
than pass a file to a VMM, hence split the memory part out of the temp
file writer, which becomes a wrapper around it.

src/shared/initrd-cpio.c

@@ -9,6 +9,7 @@
 #include "fs-util.h"
 #include "initrd-cpio.h"
 #include "io-util.h"
+#include "iovec-util.h"
 #include "log.h"
 #include "machine-credential.h"
 #include "memory-util.h"
@@ -117,13 +118,11 @@ static void append_cpio_trailer(FILE *f) {
         fwrite(trailer, 1, sizeof trailer, f);
 }
 
-int initrd_cpio_credentials_to_tempfile(
+int initrd_cpio_credentials_to_memory(
                 const MachineCredentialContext *creds,
-                char **ret_path) {
+                struct iovec *ret) {
 
         _cleanup_(memstream_done) MemStream m = {};
-        _cleanup_(unlink_and_freep) char *path = NULL;
-        _cleanup_close_ int fd = -EBADF;
         _cleanup_(erase_and_freep) char *buf = NULL; /* holds plaintext credential bytes; scrub on free */
         size_t buf_size = 0;
         uint32_t inode = 1;
@@ -131,12 +130,7 @@ int initrd_cpio_credentials_to_tempfile(
         int r;
 
         assert(creds);
-        assert(ret_path);
-
-        if (creds->n_credentials == 0) {
-                *ret_path = NULL;
-                return 0;
-        }
+        assert(ret);
 
         f = memstream_init(&m);
         if (!f)
@@ -168,6 +162,31 @@ int initrd_cpio_credentials_to_tempfile(
         if (r < 0)
                 return log_error_errno(r, "Failed to finalize credentials cpio: %m");
 
+        *ret = IOVEC_MAKE(TAKE_PTR(buf), buf_size);
+        return 0;
+}
+
+int initrd_cpio_credentials_to_tempfile(
+                const MachineCredentialContext *creds,
+                char **ret_path) {
+
+        _cleanup_(unlink_and_freep) char *path = NULL;
+        _cleanup_close_ int fd = -EBADF;
+        _cleanup_(iovec_done_erase) struct iovec cpio = {}; /* holds plaintext credential bytes; scrub on free */
+        int r;
+
+        assert(creds);
+        assert(ret_path);
+
+        if (creds->n_credentials == 0) {
+                *ret_path = NULL;
+                return 0;
+        }
+
+        r = initrd_cpio_credentials_to_memory(creds, &cpio);
+        if (r < 0)
+                return r;
+
         r = tempfn_random_child(NULL, "credentials-cpio", &path);
         if (r < 0)
                 return log_error_errno(r, "Failed to generate temp file name: %m");
@@ -176,7 +195,7 @@ int initrd_cpio_credentials_to_tempfile(
         if (fd < 0)
                 return log_error_errno(fd, "Failed to create temp file %s: %m", path);
 
-        r = loop_write(fd, buf, buf_size);
+        r = loop_write(fd, cpio.iov_base, cpio.iov_len);
         if (r < 0)
                 return log_error_errno(r, "Failed to write credentials cpio: %m");
 

src/shared/initrd-cpio.h

@@ -12,3 +12,8 @@
 int initrd_cpio_credentials_to_tempfile(
                 const MachineCredentialContext *creds,
                 char **ret_path);
+
+/* Same, but returns the archive in memory. An archive is built even if there are no credentials. */
+int initrd_cpio_credentials_to_memory(
+                const MachineCredentialContext *creds,
+                struct iovec *ret);

src/test/test-initrd-cpio.c

@@ -9,12 +9,34 @@
 #include "fileio.h"
 #include "fs-util.h"
 #include "initrd-cpio.h"
+#include "iovec-util.h"
 #include "machine-credential.h"
 #include "path-util.h"
 #include "rm-rf.h"
 #include "tests.h"
 #include "tmpfile-util.h"
 
+TEST(initrd_cpio_credentials_to_memory) {
+        _cleanup_(machine_credential_context_done) MachineCredentialContext creds = {};
+        _cleanup_(iovec_done) struct iovec empty = {}, archive = {};
+
+        /* Without credentials the archive still carries the directories and the trailer */
+        ASSERT_OK(initrd_cpio_credentials_to_memory(&creds, &empty));
+        ASSERT_NOT_NULL(empty.iov_base);
+        ASSERT_GT(empty.iov_len, 0U);
+        ASSERT_EQ(empty.iov_len % 4, 0U);
+        ASSERT_NOT_NULL(memmem(empty.iov_base, empty.iov_len, "TRAILER!!!", STRLEN("TRAILER!!!")));
+        ASSERT_NOT_NULL(memmem(empty.iov_base, empty.iov_len, ".extra/system_credentials", STRLEN(".extra/system_credentials")));
+
+        ASSERT_OK(machine_credential_add(&creds, "foo", "hello", 5));
+        ASSERT_OK(initrd_cpio_credentials_to_memory(&creds, &archive));
+        ASSERT_NOT_NULL(archive.iov_base);
+        ASSERT_GT(archive.iov_len, empty.iov_len);
+        ASSERT_NOT_NULL(memmem(archive.iov_base, archive.iov_len, ".extra/system_credentials/foo.cred", STRLEN(".extra/system_credentials/foo.cred")));
+        ASSERT_NOT_NULL(memmem(archive.iov_base, archive.iov_len, "hello", STRLEN("hello")));
+        ASSERT_NULL(memmem(empty.iov_base, empty.iov_len, "foo.cred", STRLEN("foo.cred")));
+}
+
 TEST_RET(initrd_cpio_credentials_basic) {
         struct stat st;
         size_t foo_size, bar_size;