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add optional transient etc
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@raballew
raballew committed Aug 8, 2023
1 parent 09160c1 commit 2222aa9
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Showing 2 changed files with 91 additions and 9 deletions.
10 changes: 8 additions & 2 deletions man/ostree-prepare-root.xml
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Original file line number Diff line number Diff line change
Expand Up @@ -114,8 +114,14 @@ License along with this library. If not, see <https://www.gnu.org/licenses/>.
<listitem><para>A boolean value; the default is false. If this is set to <literal>true</literal>, then the <literal>/sysroot</literal> mount point is mounted read-only.</para></listitem>
</varlistentry>
</variablelist>
</refsect1>

<variablelist>
<varlistentry>
<term><varname>sysroot.etc</varname></term>
<listitem><para>A string value; the default is persitent. If this is set to <literal>transient</literal>, then the <literal>/sysroot</literal> mount point is mounted transiently i.e. a non-persistent location.</para></listitem>
</varlistentry>
</variablelist>
</refsect1>

<refsect1>
<title>systemd</title>
Expand All @@ -136,4 +142,4 @@ License along with this library. If not, see <https://www.gnu.org/licenses/>.
</para>
</refsect1>

</refentry>
</refentry>
90 changes: 83 additions & 7 deletions src/switchroot/ostree-prepare-root.c
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Original file line number Diff line number Diff line change
Expand Up @@ -82,6 +82,7 @@ const char *config_roots[] = { "/usr/lib", "/etc" };

#define SYSROOT_KEY "sysroot"
#define READONLY_KEY "readonly"
#define ETC_KEY "etc" // Possible values = "persistent" "transient"

// The kernel argument we support to configure composefs.
#define OT_COMPOSEFS_KARG "ot-composefs"
Expand Down Expand Up @@ -326,6 +327,29 @@ load_composefs_config (GError **error)
return g_steal_pointer (&ret);
}

static gboolean
copy_selinux_context (const char *src_path, const char *dst_path, GError **error)
{
ssize_t bytes_read, real_size;

if (TEMP_FAILURE_RETRY (bytes_read = lgetxattr (src_path, "security.selinux", NULL, 0)) < 0)
{
if (errno == ENODATA || errno == ENOTSUP)
return TRUE; /* no selinux context, we're done */
return glnx_throw_errno_prefix (error, "lgetxattr(security.selinux)");
}

g_autofree guint8 *buf = g_malloc (bytes_read);
if (TEMP_FAILURE_RETRY (real_size = lgetxattr (src_path, "security.selinux", buf, bytes_read))
< 0)
return glnx_throw_errno_prefix (error, "lgetxattr(security.selinux)");

if (lsetxattr (dst_path, "security.selinux", buf, real_size, 0) < 0)
return glnx_throw_errno_prefix (error, "lsetxattr(security.selinux)");

return TRUE;
}

int
main (int argc, char *argv[])
{
Expand Down Expand Up @@ -569,18 +593,70 @@ main (int argc, char *argv[])
}
}

g_autofree char *etc_config = NULL;
if (!ot_keyfile_get_value_with_default (config, SYSROOT_KEY, ETC_KEY, "persistent", &etc_config,
&error))
errx (EXIT_FAILURE, "failed to parse %s.%s: %s", SYSROOT_KEY, ETC_KEY, error->message);
bool etc_transient = false;
if (g_str_equal (etc_config, "persistent"))
etc_transient = false;
else if (g_str_equal (etc_config, "transient"))
etc_transient = true;
else
errx (EXIT_FAILURE, "Invalid %s.%s: %s", SYSROOT_KEY, ETC_KEY, etc_config);

// In theory these could be distinct, but no reason to try to support it.
if (etc_transient && !sysroot_readonly)
errx (EXIT_FAILURE, "Must specify %s.%s for %s.%s=transient", SYSROOT_KEY, READONLY_KEY,
SYSROOT_KEY, ETC_KEY);

/* Prepare /etc.
* No action required if sysroot is writable. Otherwise, a bind-mount for
* the deployment needs to be created and remounted as read/write. */
if (sysroot_readonly || using_composefs)
{
/* Bind-mount /etc (at deploy path), and remount as writable. */
if (mount ("etc", TMP_SYSROOT "/etc", NULL, MS_BIND | MS_SILENT, NULL) < 0)
err (EXIT_FAILURE, "failed to prepare /etc bind-mount at /sysroot.tmp/etc");
if (mount (TMP_SYSROOT "/etc", TMP_SYSROOT "/etc", NULL, MS_BIND | MS_REMOUNT | MS_SILENT,
NULL)
< 0)
err (EXIT_FAILURE, "failed to make writable /etc bind-mount at /sysroot.tmp/etc");
if (etc_transient)
{
g_autofree char *etc_ovldir
= g_build_filename (OTCORE_RUN_OSTREE_PRIVATE, "etc-transient", NULL);
g_autofree char *upper = g_build_filename (etc_ovldir, "upper", NULL);
g_autofree char *work = g_build_filename (etc_ovldir, "work", NULL);

if (mkdirat (AT_FDCWD, etc_ovldir, 0700) < 0)
err (EXIT_FAILURE, "Failed to create %s", etc_ovldir);
if (mkdirat (AT_FDCWD, upper, 0755) < 0)
err (EXIT_FAILURE, "Failed to create %s", upper);
if (mkdirat (AT_FDCWD, work, 0755) < 0)
err (EXIT_FAILURE, "Failed to create %s", work);

g_autofree char *etc_ovl_options = g_strdup_printf ("lowerdir=%s,upperdir=%s,workdir=%s",
TMP_SYSROOT "/usr/etc", upper, work);
if (mount ("overlay", TMP_SYSROOT "/etc", "overlay", MS_SILENT, etc_ovl_options) < 0)
err (EXIT_FAILURE, "failed to mount transient etc overlayfs");

g_autoptr (GError) local_error = NULL;
if (!copy_selinux_context (TMP_SYSROOT "/usr/etc", TMP_SYSROOT "/etc", &local_error))
err (EXIT_FAILURE, "failed to copy /usr/etc selinux label: %s", local_error->message);

/* We make ovldir read-only to avoid it being relabeled to
* var_run_t when /run is relabeled */
if (mount (etc_ovldir, etc_ovldir, NULL, MS_BIND | MS_SILENT, NULL) < 0)
err (EXIT_FAILURE, "failed to bind mount (class:readonly) %s", etc_ovldir);
if (mount (etc_ovldir, etc_ovldir, NULL, MS_BIND | MS_REMOUNT | MS_RDONLY | MS_SILENT,
NULL)
< 0)
err (EXIT_FAILURE, "failed to bind mount (class:readonly) %s", etc_ovldir);
}
else
{
/* Bind-mount /etc (at deploy path), and remount as writable. */
if (mount ("etc", TMP_SYSROOT "/etc", NULL, MS_BIND | MS_SILENT, NULL) < 0)
err (EXIT_FAILURE, "failed to prepare /etc bind-mount at /sysroot.tmp/etc");
if (mount (TMP_SYSROOT "/etc", TMP_SYSROOT "/etc", NULL, MS_BIND | MS_REMOUNT | MS_SILENT,
NULL)
< 0)
err (EXIT_FAILURE, "failed to make writable /etc bind-mount at /sysroot.tmp/etc");
}
}

/* Prepare /usr.
Expand Down

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