non-root: enable non-root checkpoint/restore

This commit enables checkpointing and restoring of applications as
non-root.

First goal was to enable checkpoint and restore of the env00 and
pthread00 test case.

This uses the information from opts.unprivileged and opts.cap_eff to
skip certain code paths which do not work as non-root.

Co-authored-by: Adrian Reber <areber@redhat.com>
Signed-off-by: Younes Manton <ymanton@ca.ibm.com>

criu/cgroup.c

@@ -734,6 +734,9 @@ int dump_task_cgroup(struct pstree_item *item, u32 *cg_id, struct parasite_dump_
 	unsigned int n_ctls = 0;
 	struct cg_set *cs;
 
+	if (opts.unprivileged)
+		return 0;
+
 	if (item)
 		pid = item->pid->real;
 	else
@@ -989,6 +992,9 @@ int dump_cgroups(void)
 	CgroupEntry cg = CGROUP_ENTRY__INIT;
 	int ret = -1;
 
+	if (opts.unprivileged)
+		return 0;
+
 	BUG_ON(!criu_cgset || !root_cgset);
 
 	/*

criu/config.c

@@ -700,6 +700,7 @@ int parse_options(int argc, char **argv, bool *usage_error, bool *has_exec_cmd,
 		{ "lsm-mount-context", required_argument, 0, 1099 },
 		{ "network-lock", required_argument, 0, 1100 },
 		BOOL_OPT("mntns-compat-mode", &opts.mntns_compat_mode),
+		BOOL_OPT("unprivileged", &opts.unprivileged),
 		{},
 	};
 

criu/cr-check.c

@@ -21,6 +21,7 @@
 #include <sys/prctl.h>
 #include <sched.h>
 #include <sys/mount.h>
+#include <sys/utsname.h>
 
 #include "../soccr/soccr.h"
 
@@ -515,6 +516,14 @@ static int check_ipc(void)
 {
 	int ret;
 
+	/*
+	 * Since kernel 5.16 sem_next_id can be accessed via CAP_CHECKPOINT_RESTORE, however
+	 * for non-root users access() runs with an empty set of caps and will therefore always
+	 * fail.
+	 */
+	if (opts.uid)
+		return 0;
+
 	ret = access("/proc/sys/kernel/sem_next_id", R_OK | W_OK);
 	if (!ret)
 		return 0;
@@ -1039,10 +1048,14 @@ static int check_tcp(void)
 	}
 
 	val = 1;
-	ret = setsockopt(sk, SOL_TCP, TCP_REPAIR, &val, sizeof(val));
-	if (ret < 0) {
-		pr_perror("Can't turn TCP repair mode ON");
-		goto out;
+	if (!opts.unprivileged || has_cap_net_admin(opts.cap_eff)) {
+		ret = setsockopt(sk, SOL_TCP, TCP_REPAIR, &val, sizeof(val));
+		if (ret < 0) {
+			pr_perror("Can't turn TCP repair mode ON");
+			goto out;
+		}
+	} else {
+		pr_info("Not checking for TCP repair mode. Please set CAP_NET_ADMIN\n");
 	}
 
 	optlen = sizeof(val);
@@ -1394,9 +1407,6 @@ int cr_check(void)
 	struct ns_id *ns;
 	int ret = 0;
 
-	if (!is_root_user())
-		return -1;
-
 	root_item = alloc_pstree_item();
 	if (root_item == NULL)
 		return -1;
@@ -1666,36 +1676,43 @@ static int pr_set_dumpable(int value)
 
 int check_caps(void)
 {
-	struct proc_status_creds creds;
-	int exit_code = -1;
-
-	if (parse_pid_status(PROC_SELF, &creds.s, NULL))
+	/* Read out effective capabilities and store in opts.cap_eff. */
+	if (set_opts_cap_eff())
 		goto out;
 
-	memcpy(&opts.cap_eff, &creds.cap_eff, sizeof(u32) * PROC_CAP_SIZE);
-
+	/*
+	 * No matter if running as root or not. CRIU always needs
+	 * at least these capabilities.
+	 */
 	if (!has_cap_checkpoint_restore(opts.cap_eff))
 		goto out;
 
 	/* For some things we need to know if we are running as root. */
 	opts.uid = geteuid();
 
-	if (opts.uid) {
-		/*
-		 * At his point we know we are running as non-root with the necessary
-		 * capabilities available. Now we have to make the process dumpable
-		 * so that /proc/self is not owned by root.
-		 */
-		if (pr_set_dumpable(1))
-			return -1;
+	if (!opts.uid) {
+		/* CRIU is running as root. No further checks are necessary. */
+		return 0;
 	}
 
-	exit_code = 0;
+	if (!opts.unprivileged) {
+		pr_msg("Running as non-root requires '--unprivileged'\n");
+		pr_msg("Please consult the documentation for limitations when running as non-root\n");
+		return -1;
+	}
+
+	/*
+	 * At his point we know we are running as non-root with the necessary
+	 * capabilities available. Now we have to make the process dumpable
+	 * so that /proc/self is not owned by root.
+	 */
+	if (pr_set_dumpable(1))
+		return -1;
+
+	return 0;
 out:
-	if (exit_code) {
-		pr_msg("CRIU needs to have the CAP_SYS_ADMIN or the CAP_CHECKPOINT_RESTORE capability: \n");
-		pr_msg("setcap cap_checkpoint_restore+eip %s\n", opts.argv_0);
-	}
+	pr_msg("CRIU needs to have the CAP_SYS_ADMIN or the CAP_CHECKPOINT_RESTORE capability: \n");
+	pr_msg("setcap cap_checkpoint_restore+eip %s\n", opts.argv_0);
 
-	return exit_code;
+	return -1;
 }

criu/cr-restore.c

@@ -1809,6 +1809,9 @@ static int restore_task_with_children(void *_arg)
 				goto err;
 		}
 
+		if (set_opts_cap_eff())
+			goto err;
+
 		/* Wait prepare_userns */
 		if (restore_finish_ns_stage(CR_STATE_ROOT_TASK, CR_STATE_PREPARE_NAMESPACES) < 0)
 			goto err;

criu/cr-service.c

@@ -14,6 +14,7 @@
 #include <sys/stat.h>
 #include <arpa/inet.h>
 #include <sched.h>
+#include <sys/prctl.h>
 
 #include "version.h"
 #include "crtools.h"
@@ -409,6 +410,12 @@ static int setup_opts_from_req(int sk, CriuOpts *req)
 		pr_debug("Would overwrite RPC settings with values from %s\n", req->config_file);
 	}
 
+	if (req->has_unprivileged)
+		opts.unprivileged = req->unprivileged;
+
+	if (check_caps())
+		return 1;
+
 	if (kerndat_init())
 		return 1;
 

criu/crtools.c

@@ -185,6 +185,9 @@ int main(int argc, char *argv[], char *envp[])
 		return cr_service_work(atoi(argv[optind + 1]));
 	}
 
+	if (check_caps())
+		return 1;
+
 	if (opts.imgs_dir == NULL)
 		SET_CHAR_OPTS(imgs_dir, ".");
 
@@ -414,6 +417,8 @@ usage:
 	       "  --network-lock METHOD\n"
 	       "                      network locking/unlocking method; argument\n"
 	       "                      can be 'nftables' or 'iptables' (default).\n"
+	       "  --unprivileged        accept limitations when running as non-root\n"
+	       "                        consult documentation for further details\n"
 	       "\n"
 	       "* External resources support:\n"
 	       "  --external RES        dump objects from this list as external resources:\n"

criu/fdstore.c

@@ -13,6 +13,8 @@
 #include "rst-malloc.h"
 #include "log.h"
 #include "util.h"
+#include "cr_options.h"
+#include "util-caps.h"
 
 /* clang-format off */
 static struct fdstore_desc {
@@ -27,6 +29,8 @@ int fdstore_init(void)
 	uint32_t buf[2] = { INT_MAX / 2, INT_MAX / 2 };
 	struct sockaddr_un addr;
 	unsigned int addrlen;
+	int rcv_opt_name;
+	int snd_opt_name;
 	struct stat st;
 	int sk, ret;
 
@@ -49,8 +53,16 @@ int fdstore_init(void)
 		return -1;
 	}
 
-	if (setsockopt(sk, SOL_SOCKET, SO_SNDBUFFORCE, &buf[0], sizeof(buf[0])) < 0 ||
-	    setsockopt(sk, SOL_SOCKET, SO_RCVBUFFORCE, &buf[1], sizeof(buf[1])) < 0) {
+	if (!opts.unprivileged || has_cap_net_admin(opts.cap_eff)) {
+		rcv_opt_name = SO_RCVBUFFORCE;
+		snd_opt_name = SO_SNDBUFFORCE;
+	} else {
+		rcv_opt_name = SO_RCVBUF;
+		snd_opt_name = SO_SNDBUF;
+	}
+
+	if (setsockopt(sk, SOL_SOCKET, snd_opt_name, &buf[0], sizeof(buf[0])) < 0 ||
+	    setsockopt(sk, SOL_SOCKET, rcv_opt_name, &buf[1], sizeof(buf[1])) < 0) {
 		pr_perror("Unable to set SO_SNDBUFFORCE/SO_RCVBUFFORCE");
 		close(sk);
 		return -1;

criu/files.c

@@ -21,7 +21,7 @@
 #include "image.h"
 #include "common/list.h"
 #include "rst-malloc.h"
-#include "util-pie.h"
+#include "util-caps.h"
 #include "common/lock.h"
 #include "sockets.h"
 #include "pstree.h"
@@ -1346,10 +1346,35 @@ static int fchroot(int fd)
 	return chroot(".");
 }
 
+static int need_chroot(int saved_root)
+{
+	struct stat saved_root_stat, cur_root_stat;
+	int psd;
+
+	if (fstat(saved_root, &saved_root_stat) == -1) {
+		pr_perror("Failed to stat saved root dir");
+		return -1;
+	}
+
+	psd = open_pid_proc(PROC_SELF);
+	if (psd < 0) {
+		pr_perror("Failed to open PROC_SELF");
+		return -1;
+	}
+
+	if (fstatat(psd, "root", &cur_root_stat, 0) == -1) {
+		pr_perror("Failed to stat current root dir");
+		return -1;
+	}
+
+	return saved_root_stat.st_ino != cur_root_stat.st_ino || saved_root_stat.st_dev != cur_root_stat.st_dev;
+}
+
 int restore_fs(struct pstree_item *me)
 {
 	int dd_root = -1, dd_cwd = -1, ret, err = -1;
 	struct rst_info *ri = rsti(me);
+	bool do_chroot = true;
 
 	/*
 	 * First -- open both descriptors. We will not
@@ -1368,15 +1393,24 @@ int restore_fs(struct pstree_item *me)
 		goto out;
 	}
 
+	/*
+	 * In unprivileged mode chroot() may fail if we don't have
+	 * sufficient privileges, therefore only do it if the process
+	 * is actually chrooted.
+	 */
+	if (opts.unprivileged)
+		do_chroot = need_chroot(dd_root);
+
 	/*
 	 * Now do chroot/chdir. Chroot goes first as it calls chdir into
 	 * dd_root so we'd need to fix chdir after it anyway.
 	 */
-
-	ret = fchroot(dd_root);
-	if (ret < 0) {
-		pr_perror("Can't change root");
-		goto out;
+	if (do_chroot) {
+		ret = fchroot(dd_root);
+		if (ret < 0) {
+			pr_perror("Can't change root");
+			goto out;
+		}
 	}
 
 	ret = fchdir(dd_cwd);

criu/image.c

@@ -226,7 +226,8 @@ int prepare_inventory(InventoryEntry *he)
 	if (get_task_ids(&crt.i))
 		return -1;
 
-	he->has_root_cg_set = true;
+	if (!opts.unprivileged)
+		he->has_root_cg_set = true;
 	if (dump_task_cgroup(NULL, &he->root_cg_set, NULL))
 		return -1;
 

criu/include/cr_options.h

@@ -2,6 +2,7 @@
 #define __CR_OPTIONS_H__
 
 #include <stdbool.h>
+#include <sys/capability.h>
 #include "common/config.h"
 #include "common/list.h"
 #include "int.h"
@@ -223,8 +224,14 @@ struct cr_options {
 	 * CAP_CHECKPOINT_RESTORE or CAP_SYS_ADMIN
 	 */
 	uid_t uid;
-	/* This contains the value from /proc/pid/status: CapEff */
-	u32 cap_eff[CR_CAP_SIZE];
+	/* This contains the value from capget()->effective */
+	u32 cap_eff[_LINUX_CAPABILITY_U32S_3];
+	/*
+	 * If CRIU should be running as non-root with the help of
+	 * CAP_CHECKPOINT_RESTORE or CAP_SYS_ADMIN the user should
+	 * explicitly request it as it comes with many limitations.
+	 */
+	int unprivileged;
 };
 
 extern struct cr_options opts;

criu/include/util.h

@@ -386,6 +386,8 @@ extern int mount_detached_fs(const char *fsname);
 
 extern char *get_legacy_iptables_bin(bool ipv6);
 
+extern int set_opts_cap_eff(void);
+
 extern ssize_t read_all(int fd, void *buf, size_t size);
 extern ssize_t write_all(int fd, const void *buf, size_t size);
 

criu/namespaces.c

@@ -28,6 +28,7 @@
 #include "cgroup.h"
 #include "fdstore.h"
 #include "kerndat.h"
+#include "util-caps.h"
 
 #include "protobuf.h"
 #include "util.h"
@@ -1623,10 +1624,12 @@ int collect_namespaces(bool for_dump)
 
 int prepare_userns_creds(void)
 {
-	/* UID and GID must be set after restoring /proc/PID/{uid,gid}_maps */
-	if (setuid(0) || setgid(0) || setgroups(0, NULL)) {
-		pr_perror("Unable to initialize id-s");
-		return -1;
+	if (!opts.unprivileged || has_cap_setuid(opts.cap_eff)) {
+		/* UID and GID must be set after restoring /proc/PID/{uid,gid}_maps */
+		if (setuid(0) || setgid(0) || setgroups(0, NULL)) {
+			pr_perror("Unable to initialize id-s");
+			return -1;
+		}
 	}
 
 	/*

criu/pie/restorer.c

@@ -184,7 +184,7 @@ static int lsm_set_label(char *label, char *type, int procfd)
 	return 0;
 }
 
-static int restore_creds(struct thread_creds_args *args, int procfd, int lsm_type)
+static int restore_creds(struct thread_creds_args *args, int procfd, int lsm_type, uid_t uid)
 {
 	CredsEntry *ce = &args->creds;
 	int b, i, ret;
@@ -211,10 +211,12 @@ static int restore_creds(struct thread_creds_args *args, int procfd, int lsm_typ
 	 * lose caps bits when changing xids.
 	 */
 
-	ret = sys_prctl(PR_SET_SECUREBITS, 1 << SECURE_NO_SETUID_FIXUP, 0, 0, 0);
-	if (ret) {
-		pr_err("Unable to set SECURE_NO_SETUID_FIXUP: %d\n", ret);
-		return -1;
+	if (!uid) {
+		ret = sys_prctl(PR_SET_SECUREBITS, 1 << SECURE_NO_SETUID_FIXUP, 0, 0, 0);
+		if (ret) {
+			pr_err("Unable to set SECURE_NO_SETUID_FIXUP: %d\n", ret);
+			return -1;
+		}
 	}
 
 	/*
@@ -252,10 +254,12 @@ static int restore_creds(struct thread_creds_args *args, int procfd, int lsm_typ
 	 * special state any longer.
 	 */
 
-	ret = sys_prctl(PR_SET_SECUREBITS, ce->secbits, 0, 0, 0);
-	if (ret) {
-		pr_err("Unable to set PR_SET_SECUREBITS: %d\n", ret);
-		return -1;
+	if (!uid) {
+		ret = sys_prctl(PR_SET_SECUREBITS, ce->secbits, 0, 0, 0);
+		if (ret) {
+			pr_err("Unable to set PR_SET_SECUREBITS: %d\n", ret);
+			return -1;
+		}
 	}
 
 	/*
@@ -634,7 +638,7 @@ long __export_restore_thread(struct thread_restore_args *args)
 	if (restore_seccomp(args))
 		BUG();
 
-	ret = restore_creds(args->creds_args, args->ta->proc_fd, args->ta->lsm_type);
+	ret = restore_creds(args->creds_args, args->ta->proc_fd, args->ta->lsm_type, args->ta->uid);
 	ret = ret || restore_dumpable_flag(&args->ta->mm);
 	ret = ret || restore_pdeath_sig(args);
 	if (ret)
@@ -1915,7 +1919,7 @@ long __export_restore_task(struct task_restore_args *args)
 	 * turning off TCP repair is CAP_SYS_NED_ADMIN protected,
 	 * thus restore* creds _after_ all of the above.
 	 */
-	ret = restore_creds(args->t->creds_args, args->proc_fd, args->lsm_type);
+	ret = restore_creds(args->t->creds_args, args->proc_fd, args->lsm_type, args->uid);
 	ret = ret || restore_dumpable_flag(&args->mm);
 	ret = ret || restore_pdeath_sig(args->t);
 	ret = ret || restore_child_subreaper(args->child_subreaper);

criu/timens.c

@@ -5,6 +5,7 @@
 #include "proc_parse.h"
 #include "namespaces.h"
 #include "timens.h"
+#include "cr_options.h"
 
 #include "protobuf.h"
 #include "images/timens.pb-c.h"
@@ -57,6 +58,9 @@ int prepare_timens(int id)
 	struct timespec ts;
 	struct timespec prev_moff = {}, prev_boff = {};
 
+	if (opts.unprivileged)
+		return 0;
+
 	img = open_image(CR_FD_TIMENS, O_RSTR, id);
 	if (!img)
 		return -1;

criu/util.c

@@ -41,6 +41,7 @@
 #include "namespaces.h"
 #include "criu-log.h"
 #include "syscall.h"
+#include "util-caps.h"
 
 #include "clone-noasan.h"
 #include "cr_options.h"
@@ -1426,6 +1427,9 @@ void rlimit_unlimit_nofile(void)
 {
 	struct rlimit new;
 
+	if (opts.unprivileged && !has_cap_sys_resource(opts.cap_eff))
+		return;
+
 	new.rlim_cur = kdat.sysctl_nr_open;
 	new.rlim_max = kdat.sysctl_nr_open;
 
@@ -2064,3 +2068,21 @@ out:
 	xfree(free_path);
 	return mp_path;
 }
+
+int set_opts_cap_eff(void)
+{
+	struct __user_cap_header_struct cap_header;
+	struct __user_cap_data_struct cap_data[_LINUX_CAPABILITY_U32S_3];
+	int i;
+
+	cap_header.version = _LINUX_CAPABILITY_VERSION_3;
+	cap_header.pid = getpid();
+
+	if (capget(&cap_header, &cap_data[0]))
+		return -1;
+
+	for (i = 0; i < _LINUX_CAPABILITY_U32S_3; i++)
+		memcpy(&opts.cap_eff[i], &cap_data[i].effective, sizeof(u32));
+
+	return 0;
+}

images/rpc.proto

@@ -139,6 +139,7 @@ message criu_opts {
 	optional criu_network_lock_method	network_lock		= 64 [default = IPTABLES];
 	optional bool			mntns_compat_mode	= 65;
 	optional bool			skip_file_rwx_check	= 66;
+	optional bool			unprivileged		= 67;
 /*	optional bool			check_mounts		= 128;	*/
 }
 

lib/c/criu.c

@@ -566,6 +566,17 @@ void criu_set_skip_file_rwx_check(bool skip_file_rwx_check)
 	criu_local_set_skip_file_rwx_check(global_opts, skip_file_rwx_check);
 }
 
+void criu_local_set_unprivileged(criu_opts *opts, bool unprivileged)
+{
+	opts->rpc->has_unprivileged = true;
+	opts->rpc->unprivileged = unprivileged;
+}
+
+void criu_set_unprivileged(bool unprivileged)
+{
+	criu_local_set_unprivileged(global_opts, unprivileged);
+}
+
 void criu_local_set_orphan_pts_master(criu_opts *opts, bool orphan_pts_master)
 {
 	opts->rpc->has_orphan_pts_master = true;

lib/c/criu.h

@@ -79,6 +79,7 @@ void criu_set_weak_sysctls(bool val);
 void criu_set_evasive_devices(bool evasive_devices);
 void criu_set_shell_job(bool shell_job);
 void criu_set_skip_file_rwx_check(bool skip_file_rwx_check);
+void criu_set_unprivileged(bool unprivileged);
 void criu_set_orphan_pts_master(bool orphan_pts_master);
 void criu_set_file_locks(bool file_locks);
 void criu_set_track_mem(bool track_mem);