Take user namespaces into account in policy checks

Change file related checks to use user namespaces and make
sure involved uids/gids are mappable in the current
namespace.

Note that checks without file ownership information will
still not take user namespaces into account, as some of
these should be handled via 'zfs allow' (otherwise root in a
user namespace could issue commands such as `zpool export`).

This also adds an initial user namespace regression test
for the setgid bit loss, with a user_ns_exec helper usable
in further tests.

Additionally, configure checks for the required user
namespace related features are added for:
  * ns_capable
  * kuid/kgid_has_mapping()
  * user_ns in cred_t

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>
Closes #6800
Closes #7270

config/kernel-userns-capabilities.m4

@@ -0,0 +1,67 @@
+dnl #
+dnl # 2.6.38 API change
+dnl # ns_capable() was introduced
+dnl #
+AC_DEFUN([ZFS_AC_KERNEL_NS_CAPABLE], [
+	AC_MSG_CHECKING([whether ns_capable exists])
+	ZFS_LINUX_TRY_COMPILE([
+		#include <linux/capability.h>
+	],[
+		ns_capable((struct user_namespace *)NULL, CAP_SYS_ADMIN);
+	],[
+		AC_MSG_RESULT(yes)
+		AC_DEFINE(HAVE_NS_CAPABLE, 1,
+		    [ns_capable exists])
+	],[
+		AC_MSG_RESULT(no)
+	])
+])
+
+dnl #
+dnl # 2.6.39 API change
+dnl # struct user_namespace was added to struct cred_t as
+dnl # cred->user_ns member
+dnl # Note that current_user_ns() was added in 2.6.28.
+dnl #
+AC_DEFUN([ZFS_AC_KERNEL_CRED_USER_NS], [
+	AC_MSG_CHECKING([whether cred_t->user_ns exists])
+	ZFS_LINUX_TRY_COMPILE([
+		#include <linux/cred.h>
+	],[
+		struct cred cr;
+		cr.user_ns = (struct user_namespace *)NULL;
+	],[
+		AC_MSG_RESULT(yes)
+		AC_DEFINE(HAVE_CRED_USER_NS, 1,
+		    [cred_t->user_ns exists])
+	],[
+		AC_MSG_RESULT(no)
+	])
+])
+
+dnl #
+dnl # 3.4 API change
+dnl # kuid_has_mapping() and kgid_has_mapping() were added to distinguish
+dnl # between internal kernel uids/gids and user namespace uids/gids.
+dnl #
+AC_DEFUN([ZFS_AC_KERNEL_KUID_HAS_MAPPING], [
+	AC_MSG_CHECKING([whether kuid_has_mapping/kgid_has_mapping exist])
+	ZFS_LINUX_TRY_COMPILE([
+		#include <linux/uidgid.h>
+	],[
+		kuid_has_mapping((struct user_namespace *)NULL, KUIDT_INIT(0));
+		kgid_has_mapping((struct user_namespace *)NULL, KGIDT_INIT(0));
+	],[
+		AC_MSG_RESULT(yes)
+		AC_DEFINE(HAVE_KUID_HAS_MAPPING, 1,
+		    [kuid_has_mapping/kgid_has_mapping exist])
+	],[
+		AC_MSG_RESULT(no)
+	])
+])
+
+AC_DEFUN([ZFS_AC_KERNEL_USERNS_CAPABILITIES], [
+	ZFS_AC_KERNEL_NS_CAPABLE
+	ZFS_AC_KERNEL_CRED_USER_NS
+	ZFS_AC_KERNEL_KUID_HAS_MAPPING
+])

config/kernel.m4

@@ -126,6 +126,7 @@ AC_DEFUN([ZFS_AC_CONFIG_KERNEL], [
 	ZFS_AC_KERNEL_CURRENT_TIME
 	ZFS_AC_KERNEL_GLOBAL_PAGE_STATE
 	ZFS_AC_KERNEL_ACL_HAS_REFCOUNT
+	ZFS_AC_KERNEL_USERNS_CAPABILITIES
 
 	AS_IF([test "$LINUX_OBJ" != "$LINUX"], [
 		KERNELMAKE_PARAMS="$KERNELMAKE_PARAMS O=$LINUX_OBJ"

configure.ac

@@ -153,6 +153,7 @@ AC_CONFIG_FILES([
 	tests/zfs-tests/callbacks/Makefile
 	tests/zfs-tests/cmd/Makefile
 	tests/zfs-tests/cmd/chg_usr_exec/Makefile
+	tests/zfs-tests/cmd/user_ns_exec/Makefile
 	tests/zfs-tests/cmd/devname2devid/Makefile
 	tests/zfs-tests/cmd/dir_rd_update/Makefile
 	tests/zfs-tests/cmd/file_check/Makefile
@@ -284,6 +285,7 @@ AC_CONFIG_FILES([
 	tests/zfs-tests/tests/functional/threadsappend/Makefile
 	tests/zfs-tests/tests/functional/tmpfile/Makefile
 	tests/zfs-tests/tests/functional/truncate/Makefile
+	tests/zfs-tests/tests/functional/user_namespace/Makefile
 	tests/zfs-tests/tests/functional/userquota/Makefile
 	tests/zfs-tests/tests/functional/upgrade/Makefile
 	tests/zfs-tests/tests/functional/vdev_zaps/Makefile

module/zfs/policy.c

@@ -42,19 +42,47 @@
  * all other cases this function must fail and return the passed err.
  */
 static int
-priv_policy(const cred_t *cr, int capability, boolean_t all, int err)
+priv_policy_ns(const cred_t *cr, int capability, boolean_t all, int err,
+    struct user_namespace *ns)
 {
 	ASSERT3S(all, ==, B_FALSE);
 
 	if (cr != CRED() && (cr != kcred))
 		return (err);
 
+#if defined(CONFIG_USER_NS) && defined(HAVE_NS_CAPABLE)
+	if (!(ns ? ns_capable(ns, capability) : capable(capability)))
+#else
 	if (!capable(capability))
+#endif
 		return (err);
 
 	return (0);
 }
 
+static int
+priv_policy(const cred_t *cr, int capability, boolean_t all, int err)
+{
+	return (priv_policy_ns(cr, capability, all, err, NULL));
+}
+
+static int
+priv_policy_user(const cred_t *cr, int capability, boolean_t all, int err)
+{
+	/*
+	 * All priv_policy_user checks are preceeded by kuid/kgid_has_mapping()
+	 * checks. If we cannot do them, we shouldn't be using ns_capable()
+	 * since we don't know whether the affected files are valid in our
+	 * namespace. Note that kuid_has_mapping() came after cred->user_ns, so
+	 * we shouldn't need to re-check for HAVE_CRED_USER_NS
+	 */
+#if defined(CONFIG_USER_NS) && defined(HAVE_KUID_HAS_MAPPING)
+	return (priv_policy_ns(cr, capability, all, err, cr->user_ns));
+#else
+	return (priv_policy_ns(cr, capability, all, err, NULL));
+#endif
+}
+
 /*
  * Checks for operations that are either client-only or are used by
  * both clients and servers.
@@ -102,10 +130,15 @@ secpolicy_vnode_any_access(const cred_t *cr, struct inode *ip, uid_t owner)
 	if (zpl_inode_owner_or_capable(ip))
 		return (0);
 
-	if (priv_policy(cr, CAP_DAC_OVERRIDE, B_FALSE, EPERM) == 0)
+#if defined(CONFIG_USER_NS) && defined(HAVE_KUID_HAS_MAPPING)
+	if (!kuid_has_mapping(cr->user_ns, SUID_TO_KUID(owner)))
+		return (EPERM);
+#endif
+
+	if (priv_policy_user(cr, CAP_DAC_OVERRIDE, B_FALSE, EPERM) == 0)
 		return (0);
 
-	if (priv_policy(cr, CAP_DAC_READ_SEARCH, B_FALSE, EPERM) == 0)
+	if (priv_policy_user(cr, CAP_DAC_READ_SEARCH, B_FALSE, EPERM) == 0)
 		return (0);
 
 	return (EPERM);
@@ -120,7 +153,12 @@ secpolicy_vnode_chown(const cred_t *cr, uid_t owner)
 	if (crgetfsuid(cr) == owner)
 		return (0);
 
-	return (priv_policy(cr, CAP_FOWNER, B_FALSE, EPERM));
+#if defined(CONFIG_USER_NS) && defined(HAVE_KUID_HAS_MAPPING)
+	if (!kuid_has_mapping(cr->user_ns, SUID_TO_KUID(owner)))
+		return (EPERM);
+#endif
+
+	return (priv_policy_user(cr, CAP_FOWNER, B_FALSE, EPERM));
 }
 
 /*
@@ -152,7 +190,12 @@ secpolicy_vnode_setdac(const cred_t *cr, uid_t owner)
 	if (crgetfsuid(cr) == owner)
 		return (0);
 
-	return (priv_policy(cr, CAP_FOWNER, B_FALSE, EPERM));
+#if defined(CONFIG_USER_NS) && defined(HAVE_KUID_HAS_MAPPING)
+	if (!kuid_has_mapping(cr->user_ns, SUID_TO_KUID(owner)))
+		return (EPERM);
+#endif
+
+	return (priv_policy_user(cr, CAP_FOWNER, B_FALSE, EPERM));
 }
 
 /*
@@ -175,8 +218,12 @@ secpolicy_vnode_setid_retain(const cred_t *cr, boolean_t issuidroot)
 int
 secpolicy_vnode_setids_setgids(const cred_t *cr, gid_t gid)
 {
+#if defined(CONFIG_USER_NS) && defined(HAVE_KUID_HAS_MAPPING)
+	if (!kgid_has_mapping(cr->user_ns, SGID_TO_KGID(gid)))
+		return (EPERM);
+#endif
 	if (crgetfsgid(cr) != gid && !groupmember(gid, cr))
-		return (priv_policy(cr, CAP_FSETID, B_FALSE, EPERM));
+		return (priv_policy_user(cr, CAP_FSETID, B_FALSE, EPERM));
 
 	return (0);
 }
@@ -222,7 +269,12 @@ secpolicy_vnode_setid_modify(const cred_t *cr, uid_t owner)
 	if (crgetfsuid(cr) == owner)
 		return (0);
 
-	return (priv_policy(cr, CAP_FSETID, B_FALSE, EPERM));
+#if defined(CONFIG_USER_NS) && defined(HAVE_KUID_HAS_MAPPING)
+	if (!kuid_has_mapping(cr->user_ns, SUID_TO_KUID(owner)))
+		return (EPERM);
+#endif
+
+	return (priv_policy_user(cr, CAP_FSETID, B_FALSE, EPERM));
 }
 
 /*

tests/runfiles/linux.run

@@ -648,6 +648,10 @@ tags = ['functional', 'truncate']
 tests = [ 'upgrade_userobj_001_pos' ]
 tags = ['functional', 'upgrade']
 
+[tests/functional/user_namespace]
+tests = ['user_namespace_001']
+tags = ['functional', 'user_namespace']
+
 [tests/functional/userquota]
 tests = [
     'userquota_001_pos', 'userquota_002_pos', 'userquota_003_pos',

tests/zfs-tests/cmd/Makefile.am

@@ -2,6 +2,7 @@ EXTRA_DIST = file_common.h
 
 SUBDIRS = \
 	chg_usr_exec \
+	user_ns_exec \
 	devname2devid \
 	dir_rd_update \
 	file_check \

tests/zfs-tests/cmd/user_ns_exec/.gitignore

@@ -0,0 +1 @@
+/user_ns_exec

tests/zfs-tests/cmd/user_ns_exec/Makefile.am

@@ -0,0 +1,6 @@
+include $(top_srcdir)/config/Rules.am
+
+pkgexecdir = $(datadir)/@PACKAGE@/zfs-tests/bin
+
+pkgexec_PROGRAMS = user_ns_exec
+user_ns_exec_SOURCES = user_ns_exec.c