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core: add a per-unit setting MountAPIVFS= for mounting /dev, /proc, /sys in conjunction with RootDirectory= 

This adds a boolean unit file setting MountAPIVFS=. If set, the three
main API VFS mounts will be mounted for the service. This only has an
effect on RootDirectory=, which it makes a ton times more useful.

(This is basically the /dev + /proc + /sys mounting code posted in the
original #4727, but rebased on current git, and with the automatic logic
replaced by explicit logic controlled by a unit file setting)
This commit is contained in:
Lennart Poettering 2016-12-22 23:34:35 +01:00
parent 1eb7e08e20
commit 5d997827e2
8 changed files with 129 additions and 16 deletions
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18
man/systemd.exec.xml
View File

@ -132,8 +132,22 @@
the <function>chroot()</function> jail. Note that setting this parameter might result in additional
dependencies to be added to the unit (see above).</para>
<para>The <varname>PrivateUsers=</varname> setting is particularly useful in conjunction with
<varname>RootDirectory=</varname>. For details, see below.</para></listitem>
<para>The <varname>MountAPIVFS=</varname> and <varname>PrivateUsers=</varname> settings are particularly useful
in conjunction with <varname>RootDirectory=</varname>. For details, see below.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>MountAPIVFS=</varname></term>
<listitem><para>Takes a boolean argument. If on, a private mount namespace for the unit's processes is created
and the API file systems <filename>/proc</filename>, <filename>/sys</filename> and <filename>/dev</filename>
will be mounted inside of it, unless they are already mounted. Note that this option has no effect unless used
in conjunction with <varname>RootDirectory=</varname> as these three mounts are generally mounted in the host
anyway, and unless the root directory is changed the private mount namespace will be a 1:1 copy of the host's,
and include these three mounts. Note that the <filename>/dev</filename> file system of the host is bind mounted
if this option is used without <varname>PrivateDevices=</varname>. To run the service with a private, minimal
version of <filename>/dev/</filename>, combine this option with
<varname>PrivateDevices=</varname>.</para></listitem>
</varlistentry>
<varlistentry>

5
src/core/dbus-execute.c
View File

@ -828,6 +828,7 @@ const sd_bus_vtable bus_exec_vtable[] = {
SD_BUS_PROPERTY("RestrictNamespaces", "t", bus_property_get_ulong, offsetof(ExecContext, restrict_namespaces), SD_BUS_VTABLE_PROPERTY_CONST),
SD_BUS_PROPERTY("BindPaths", "a(ssbt)", property_get_bind_paths, 0, SD_BUS_VTABLE_PROPERTY_CONST),
SD_BUS_PROPERTY("BindReadOnlyPaths", "a(ssbt)", property_get_bind_paths, 0, SD_BUS_VTABLE_PROPERTY_CONST),
SD_BUS_PROPERTY("MountAPIVFS", "b", bus_property_get_bool, offsetof(ExecContext, mount_apivfs), SD_BUS_VTABLE_PROPERTY_CONST),
SD_BUS_VTABLE_END
};
@ -1207,7 +1208,7 @@ int bus_exec_context_set_transient_property(
"PrivateTmp", "PrivateDevices", "PrivateNetwork", "PrivateUsers",
"NoNewPrivileges", "SyslogLevelPrefix", "MemoryDenyWriteExecute",
"RestrictRealtime", "DynamicUser", "RemoveIPC", "ProtectKernelTunables",
"ProtectKernelModules", "ProtectControlGroups")) {
"ProtectKernelModules", "ProtectControlGroups", "MountAPIVFS")) {
int b;
r = sd_bus_message_read(message, "b", &b);
@ -1247,6 +1248,8 @@ int bus_exec_context_set_transient_property(
c->protect_kernel_modules = b;
else if (streq(name, "ProtectControlGroups"))
c->protect_control_groups = b;
else if (streq(name, "MountAPIVFS"))
c->mount_apivfs = b;
unit_write_drop_in_private_format(u, mode, name, "%s=%s", name, yes_no(b));
}

6
src/core/execute.c
View File

@ -1662,6 +1662,9 @@ static bool exec_needs_mount_namespace(
context->protect_control_groups)
return true;
if (context->mount_apivfs)
return true;
return false;
}
@ -1942,6 +1945,7 @@ static int apply_mount_namespace(Unit *u, const ExecContext *context,
.protect_control_groups = context->protect_control_groups,
.protect_kernel_tunables = context->protect_kernel_tunables,
.protect_kernel_modules = context->protect_kernel_modules,
.mount_apivfs = context->mount_apivfs,
};
assert(context);
@ -3294,6 +3298,7 @@ void exec_context_dump(ExecContext *c, FILE* f, const char *prefix) {
"%sPrivateUsers: %s\n"
"%sProtectHome: %s\n"
"%sProtectSystem: %s\n"
"%sMountAPIVFS: %s\n"
"%sIgnoreSIGPIPE: %s\n"
"%sMemoryDenyWriteExecute: %s\n"
"%sRestrictRealtime: %s\n",
@ -3310,6 +3315,7 @@ void exec_context_dump(ExecContext *c, FILE* f, const char *prefix) {
prefix, yes_no(c->private_users),
prefix, protect_home_to_string(c->protect_home),
prefix, protect_system_to_string(c->protect_system),
prefix, yes_no(c->mount_apivfs),
prefix, yes_no(c->ignore_sigpipe),
prefix, yes_no(c->memory_deny_write_execute),
prefix, yes_no(c->restrict_realtime));

1
src/core/execute.h
View File

@ -183,6 +183,7 @@ struct ExecContext {
bool protect_kernel_tunables;
bool protect_kernel_modules;
bool protect_control_groups;
bool mount_apivfs;
bool no_new_privileges;

1
src/core/load-fragment-gperf.gperf.m4
View File

@ -101,6 +101,7 @@ $1.PrivateUsers, config_parse_bool, 0,
$1.ProtectSystem, config_parse_protect_system, 0, offsetof($1, exec_context)
$1.ProtectHome, config_parse_protect_home, 0, offsetof($1, exec_context)
$1.MountFlags, config_parse_exec_mount_flags, 0, offsetof($1, exec_context)
$1.MountAPIVFS, config_parse_bool, 0, offsetof($1, exec_context.mount_apivfs)
$1.Personality, config_parse_personality, 0, offsetof($1, exec_context.personality)
$1.RuntimeDirectoryMode, config_parse_mode, 0, offsetof($1, exec_context.runtime_directory_mode)
$1.RuntimeDirectory, config_parse_runtime_directory, 0, offsetof($1, exec_context.runtime_directory)

111
src/core/namespace.c
View File

@ -52,10 +52,13 @@ typedef enum MountMode {
INACCESSIBLE,
BIND_MOUNT,
BIND_MOUNT_RECURSIVE,
READONLY,
PRIVATE_TMP,
PRIVATE_VAR_TMP,
PRIVATE_DEV,
BIND_DEV,
SYSFS,
PROCFS,
READONLY,
READWRITE,
} MountMode;
@ -70,13 +73,13 @@ typedef struct MountEntry {
char *source_malloc;
} MountEntry;
/*
* The following Protect tables are to protect paths and mark some of them
* READONLY, in case a path is covered by an option from another table, then
* it is marked READWRITE in the current one, and the more restrictive mode is
* applied from that other table. This way all options can be combined in a
* safe and comprehensible way for users.
*/
/* If MountAPIVFS= is used, let's mount /sys and /proc into the it, but only as a fallback if the user hasn't mounted
* something there already. These mounts are hence overriden by any other explicitly configured mounts. */
static const MountEntry apivfs_table[] = {
{ "/proc", PROCFS, false },
{ "/dev", BIND_DEV, false },
{ "/sys", SYSFS, false },
};
/* ProtectKernelTunables= option and the related filesystem APIs */
static const MountEntry protect_kernel_tunables_table[] = {
@ -465,7 +468,7 @@ static void drop_outside_root(const char *root_directory, MountEntry *m, unsigne
*n = t - m;
}
static int mount_dev(MountEntry *m) {
static int mount_private_dev(MountEntry *m) {
static const char devnodes[] =
"/dev/null\0"
"/dev/zero\0"
@ -604,6 +607,62 @@ fail:
return r;
}
static int mount_bind_dev(MountEntry *m) {
int r;
assert(m);
/* Implements the little brother of mount_private_dev(): simply bind mounts the host's /dev into the service's
* /dev. This is only used when RootDirectory= is set. */
r = path_is_mount_point(mount_entry_path(m), NULL, 0);
if (r < 0)
return log_debug_errno(r, "Unable to determine whether /dev is already mounted: %m");
if (r > 0) /* make this a NOP if /dev is already a mount point */
return 0;
if (mount("/dev", mount_entry_path(m), NULL, MS_BIND|MS_REC, NULL) < 0)
return log_debug_errno(errno, "Failed to bind mount %s: %m", mount_entry_path(m));
return 1;
}
static int mount_sysfs(MountEntry *m) {
int r;
assert(m);
r = path_is_mount_point(mount_entry_path(m), NULL, 0);
if (r < 0)
return log_debug_errno(r, "Unable to determine whether /sys is already mounted: %m");
if (r > 0) /* make this a NOP if /sys is already a mount point */
return 0;
/* Bind mount the host's version so that we get all child mounts of it, too. */
if (mount("/sys", mount_entry_path(m), NULL, MS_BIND|MS_REC, NULL) < 0)
return log_debug_errno(errno, "Failed to mount %s: %m", mount_entry_path(m));
return 1;
}
static int mount_procfs(MountEntry *m) {
int r;
assert(m);
r = path_is_mount_point(mount_entry_path(m), NULL, 0);
if (r < 0)
return log_debug_errno(r, "Unable to determine whether /proc is already mounted: %m");
if (r > 0) /* make this a NOP if /proc is already a mount point */
return 0;
/* Mount a new instance, so that we get the one that matches our user namespace, if we are running in one */
if (mount("proc", mount_entry_path(m), "proc", MS_NOSUID|MS_NOEXEC|MS_NODEV, NULL) < 0)
return log_debug_errno(errno, "Failed to mount %s: %m", mount_entry_path(m));
return 1;
}
static int mount_entry_chase(
const char *root_directory,
MountEntry *m,
@ -691,6 +750,7 @@ static int apply_mount(
case BIND_MOUNT_RECURSIVE:
/* Also chase the source mount */
r = mount_entry_chase(root_directory, m, mount_entry_source(m), &m->source_malloc);
if (r <= 0)
return r;
@ -707,7 +767,16 @@ static int apply_mount(
break;
case PRIVATE_DEV:
return mount_dev(m);
return mount_private_dev(m);
case BIND_DEV:
return mount_bind_dev(m);
case SYSFS:
return mount_sysfs(m);
case PROCFS:
return mount_procfs(m);
default:
assert_not_reached("Unknown mode");
@ -729,7 +798,7 @@ static int make_read_only(MountEntry *m, char **blacklist) {
if (mount_entry_read_only(m))
r = bind_remount_recursive(mount_entry_path(m), true, blacklist);
else if (m->mode == PRIVATE_DEV) { /* Can be readonly but the submounts can't*/
else if (m->mode == PRIVATE_DEV) { /* Superblock can be readonly but the submounts can't*/
if (mount(NULL, mount_entry_path(m), NULL, MS_REMOUNT|DEV_MOUNT_OPTIONS|MS_RDONLY, NULL) < 0)
r = -errno;
} else
@ -745,6 +814,17 @@ static int make_read_only(MountEntry *m, char **blacklist) {
return r;
}
static bool namespace_info_mount_apivfs(const NameSpaceInfo *ns_info) {
assert(ns_info);
/* ProtectControlGroups= and ProtectKernelTunables= imply MountAPIVFS=, since to protect the API VFS mounts,
* they need to be around in the first place... */
return ns_info->mount_apivfs ||
ns_info->protect_control_groups ||
ns_info->protect_kernel_tunables;
}
static unsigned namespace_calculate_mounts(
const NameSpaceInfo *ns_info,
char** read_write_paths,
@ -781,7 +861,8 @@ static unsigned namespace_calculate_mounts(
(ns_info->protect_kernel_tunables ? ELEMENTSOF(protect_kernel_tunables_table) : 0) +
(ns_info->protect_control_groups ? 1 : 0) +
(ns_info->protect_kernel_modules ? ELEMENTSOF(protect_kernel_modules_table) : 0) +
protect_home_cnt + protect_system_cnt;
protect_home_cnt + protect_system_cnt +
(namespace_info_mount_apivfs(ns_info) ? ELEMENTSOF(apivfs_table) : 0);
}
int setup_namespace(
@ -885,6 +966,12 @@ int setup_namespace(
if (r < 0)
goto finish;
if (namespace_info_mount_apivfs(ns_info)) {
r = append_static_mounts(&m, apivfs_table, ELEMENTSOF(apivfs_table), ns_info->ignore_protect_paths);
if (r < 0)
goto finish;
}
assert(mounts + n_mounts == m);
/* Prepend the root directory where that's necessary */

1
src/core/namespace.h
View File

@ -50,6 +50,7 @@ struct NameSpaceInfo {
bool protect_control_groups:1;
bool protect_kernel_tunables:1;
bool protect_kernel_modules:1;
bool mount_apivfs:1;
};
struct BindMount {

2
src/shared/bus-unit-util.c
View File

@ -208,7 +208,7 @@ int bus_append_unit_property_assignment(sd_bus_message *m, const char *assignmen
"PrivateTmp", "PrivateDevices", "PrivateNetwork", "PrivateUsers", "NoNewPrivileges",
"SyslogLevelPrefix", "Delegate", "RemainAfterElapse", "MemoryDenyWriteExecute",
"RestrictRealtime", "DynamicUser", "RemoveIPC", "ProtectKernelTunables",
"ProtectKernelModules", "ProtectControlGroups")) {
"ProtectKernelModules", "ProtectControlGroups", "MountAPIVFS")) {
r = parse_boolean(eq);
if (r < 0)