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diff --git a/sys/conf/files b/sys/conf/files
--- a/sys/conf/files
+++ b/sys/conf/files
@@ -3818,6 +3818,7 @@
kern/kern_idle.c standard
kern/kern_intr.c standard
kern/kern_jail.c standard
+kern/kern_jailmeta.c standard
kern/kern_kcov.c optional kcov \
compile-with "${NOSAN_C} ${MSAN_CFLAGS}"
kern/kern_khelp.c standard
diff --git a/sys/kern/kern_jail.c b/sys/kern/kern_jail.c
--- a/sys/kern/kern_jail.c
+++ b/sys/kern/kern_jail.c
@@ -4254,7 +4254,7 @@
/*
* Jail-related sysctls.
*/
-static SYSCTL_NODE(_security, OID_AUTO, jail, CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
+SYSCTL_NODE(_security, OID_AUTO, jail, CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
"Jails");
#if defined(INET) || defined(INET6)
diff --git a/sys/kern/kern_jailmeta.c b/sys/kern/kern_jailmeta.c
new file mode 100644
--- /dev/null
+++ b/sys/kern/kern_jailmeta.c
@@ -0,0 +1,276 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright (c) 2024 SkunkWerks GmbH
+ *
+ * This software was developed by Igor Ostapenko <igoro@FreeBSD.org>
+ * under sponsorship from SkunkWerks GmbH.
+ */
+
+#include <sys/param.h>
+#include <sys/lock.h>
+#include <sys/sx.h>
+#include <sys/kernel.h>
+#include <sys/mount.h>
+#include <sys/malloc.h>
+#include <sys/jail.h>
+#include <sys/osd.h>
+#include <sys/proc.h>
+
+
+#define JM_PARAM_NAME "meta"
+
+
+/*
+ * Buffer limit
+ *
+ * The hard limit is the actual value used during setting or modification. The
+ * soft limit is used solely by the security.jail.param.meta sysctl. The soft
+ * limit may remain higher than the hard limit to ensure that previously set
+ * long meta strings can still be correctly interpreted by end-user interfaces
+ * like jls(8).
+ */
+
+static uint32_t jm_maxbufsize_hard = 4096;
+static uint32_t jm_maxbufsize_soft = 4096;
+
+static int
+jm_sysctl_meta_maxbufsize(SYSCTL_HANDLER_ARGS)
+{
+ int error;
+ uint32_t newmax = 0;
+
+ if (req->newptr == NULL) {
+ /* read-only */
+ sx_slock(&allprison_lock);
+ error = SYSCTL_OUT(req, &jm_maxbufsize_hard,
+ sizeof(jm_maxbufsize_hard));
+ sx_sunlock(&allprison_lock);
+ } else {
+ /* read and write */
+ sx_xlock(&allprison_lock);
+ error = SYSCTL_IN(req, &newmax, sizeof(newmax));
+ if (error == 0 && newmax < 1)
+ error = EINVAL;
+ if (error == 0) {
+ jm_maxbufsize_hard = newmax;
+ if (jm_maxbufsize_hard >= jm_maxbufsize_soft)
+ jm_maxbufsize_soft = jm_maxbufsize_hard;
+ else if (TAILQ_EMPTY(&allprison))
+ /*
+ * TODO: For now, this is the simplest way to
+ * avoid O(n) iteration over all prisons in
+ * cases of a large n.
+ */
+ jm_maxbufsize_soft = jm_maxbufsize_hard;
+ }
+ sx_xunlock(&allprison_lock);
+ }
+
+ return (error);
+}
+SYSCTL_PROC(_security_jail, OID_AUTO, meta_maxbufsize,
+ CTLTYPE_U32 | CTLFLAG_RW | CTLFLAG_MPSAFE, NULL, 0,
+ jm_sysctl_meta_maxbufsize, "IU", "Maximum meta buffer size.");
+
+
+/* Jail parameter announcement */
+
+static int
+jm_sysctl_param_meta(SYSCTL_HANDLER_ARGS)
+{
+ uint32_t soft;
+
+ sx_slock(&allprison_lock);
+ soft = jm_maxbufsize_soft;
+ sx_sunlock(&allprison_lock);
+
+ return (sysctl_jail_param(oidp, arg1, soft, req));
+}
+SYSCTL_PROC(_security_jail_param, OID_AUTO, meta,
+ CTLTYPE_STRING | CTLFLAG_RW | CTLFLAG_MPSAFE, NULL, 0,
+ jm_sysctl_param_meta, "A", "Jail meta info");
+
+
+/* OSD */
+
+static u_int jm_osd_slot;
+
+static int
+jm_osd_method_set(void *obj, void *data)
+{
+ struct prison *pr = obj;
+ struct vfsoptlist *opts = data;
+ int len = 0;
+ char *osd_addr;
+ char *osd_addr_old;
+ int error;
+
+ /* Check the option presence and its len before buf allocation */
+ error = vfs_getopt(opts, JM_PARAM_NAME, NULL, &len);
+ if (error == ENOENT)
+ return (0);
+ if (error != 0)
+ return (error);
+ if (len < 1)
+ return (EINVAL);
+
+ sx_assert(&allprison_lock, SA_LOCKED);
+ if (len > jm_maxbufsize_hard) /* len includes '\0' char */
+ return (EFBIG);
+
+ /* Prepare a new buf */
+ osd_addr = NULL;
+ if (len > 1) {
+ osd_addr = malloc(len, M_PRISON, M_WAITOK);
+ error = vfs_copyopt(opts, JM_PARAM_NAME, osd_addr, len);
+ if (error != 0) {
+ free(osd_addr, M_PRISON);
+ return (error);
+ }
+ }
+
+ /* Swap bufs */
+ mtx_lock(&pr->pr_mtx);
+ osd_addr_old = osd_jail_get(pr, jm_osd_slot);
+ error = osd_jail_set(pr, jm_osd_slot, osd_addr);
+ mtx_unlock(&pr->pr_mtx);
+
+ if (error != 0)
+ osd_addr_old = osd_addr;
+
+ free(osd_addr_old, M_PRISON);
+
+ return (error);
+}
+
+static int
+jm_osd_method_get(void *obj, void *data)
+{
+ struct prison *pr = obj;
+ struct vfsoptlist *opts = data;
+ char *osd_addr = NULL;
+ char empty = '\0';
+ int error;
+
+ /* Check the option presence to avoid unnecessary locking */
+ error = vfs_getopt(opts, JM_PARAM_NAME, NULL, NULL);
+ if (error == ENOENT)
+ return (0);
+ if (error != 0)
+ return (error);
+
+ mtx_lock(&pr->pr_mtx);
+ osd_addr = osd_jail_get(pr, jm_osd_slot);
+ if (osd_addr == NULL)
+ error = vfs_setopts(opts, JM_PARAM_NAME, &empty);
+ else
+ error = vfs_setopts(opts, JM_PARAM_NAME, osd_addr);
+ mtx_unlock(&pr->pr_mtx);
+
+ return (error);
+}
+
+static int
+jm_osd_method_check(void *obj __unused, void *data)
+{
+ struct vfsoptlist *opts = data;
+ char *meta = NULL;
+ int error;
+ int len = 0;
+
+ /* Check the option presence */
+ error = vfs_getopt(opts, JM_PARAM_NAME, (void **)&meta, &len);
+ if (error == ENOENT)
+ return (0);
+ if (error != 0)
+ return (error);
+
+ if (len < 1)
+ return (EINVAL);
+ if (meta == NULL)
+ return (EINVAL);
+
+ return (0);
+}
+
+static void
+jm_osd_destructor(void *osd_addr)
+{
+ free(osd_addr, M_PRISON);
+}
+
+
+/* A jail can read its own meta */
+
+static int
+jm_sysctl_meta(SYSCTL_HANDLER_ARGS)
+{
+ struct prison *pr;
+ char empty = '\0';
+ char *tmpbuf;
+ size_t outlen;
+ int error = 0;
+
+ pr = req->td->td_ucred->cr_prison;
+
+ mtx_lock(&pr->pr_mtx);
+ arg1 = osd_jail_get(pr, jm_osd_slot);
+ if (arg1 == NULL) {
+ tmpbuf = &empty;
+ outlen = 1;
+ } else {
+ outlen = strlen(arg1) + 1;
+ if (req->oldptr != NULL) {
+ tmpbuf = malloc(outlen, M_PRISON, M_NOWAIT);
+ error = (tmpbuf == NULL) ? ENOMEM : 0;
+ if (error == 0)
+ memcpy(tmpbuf, arg1, outlen);
+ }
+ }
+ mtx_unlock(&pr->pr_mtx);
+
+ if (error != 0)
+ return (error);
+
+ if (req->oldptr == NULL)
+ SYSCTL_OUT(req, NULL, outlen);
+ else {
+ SYSCTL_OUT(req, tmpbuf, outlen);
+ if (tmpbuf != &empty)
+ free(tmpbuf, M_PRISON);
+ }
+
+ return (error);
+}
+SYSCTL_PROC(_security_jail, OID_AUTO, meta,
+ CTLTYPE_STRING | CTLFLAG_RD | CTLFLAG_MPSAFE,
+ 0, 0, jm_sysctl_meta, "A", "Jail meta info");
+
+
+/* Setup and tear down */
+
+static int
+jm_sysinit(void *arg __unused)
+{
+ osd_method_t methods[PR_MAXMETHOD] = {
+ [PR_METHOD_SET] = jm_osd_method_set,
+ [PR_METHOD_GET] = jm_osd_method_get,
+ [PR_METHOD_CHECK] = jm_osd_method_check,
+ };
+
+ jm_osd_slot = osd_jail_register(jm_osd_destructor, methods);
+
+ return (0);
+}
+
+static int
+jm_sysuninit(void *arg __unused)
+{
+ osd_jail_deregister(jm_osd_slot);
+
+ return (0);
+}
+
+SYSINIT(jailmeta, SI_SUB_DRIVERS, SI_ORDER_ANY, jm_sysinit, NULL);
+SYSUNINIT(jailmeta, SI_SUB_DRIVERS, SI_ORDER_ANY, jm_sysuninit, NULL);
diff --git a/sys/sys/jail.h b/sys/sys/jail.h
--- a/sys/sys/jail.h
+++ b/sys/sys/jail.h
@@ -376,6 +376,7 @@
/*
* Sysctls to describe jail parameters.
*/
+SYSCTL_DECL(_security_jail);
SYSCTL_DECL(_security_jail_param);
#define SYSCTL_JAIL_PARAM(module, param, type, fmt, descr) \
diff --git a/tests/sys/kern/Makefile b/tests/sys/kern/Makefile
--- a/tests/sys/kern/Makefile
+++ b/tests/sys/kern/Makefile
@@ -57,6 +57,7 @@
TEST_METADATA.sigsys+= is_exclusive="true"
ATF_TESTS_SH+= coredump_phnum_test
+ATF_TESTS_SH+= jailmeta
ATF_TESTS_SH+= sonewconn_overflow
TEST_METADATA.sonewconn_overflow+= required_programs="python"
TEST_METADATA.sonewconn_overflow+= required_user="root"
diff --git a/tests/sys/kern/jailmeta.sh b/tests/sys/kern/jailmeta.sh
new file mode 100644
--- /dev/null
+++ b/tests/sys/kern/jailmeta.sh
@@ -0,0 +1,353 @@
+#
+# SPDX-License-Identifier: BSD-2-Clause
+#
+# Copyright (c) 2024 SkunkWerks GmbH
+#
+# This software was developed by Igor Ostapenko <igoro@FreeBSD.org>
+# under sponsorship from SkunkWerks GmbH.
+#
+
+setup()
+{
+ if [ $(sysctl -n security.jail.meta_maxbufsize) -lt 10 ]; then
+ atf_skip "sysctl security.jail.meta_maxbufsize must be 10+ for testing."
+ fi
+}
+
+atf_test_case "jail_create" "cleanup"
+jail_create_head()
+{
+ atf_set descr 'Test that meta can be set upon jail creation with jail(8)'
+ atf_set require.user root
+ atf_set execenv jail
+}
+jail_create_body()
+{
+ setup
+
+ atf_check -s not-exit:0 -e match:"not found" -o ignore \
+ jls -j jail1
+
+ atf_check -s exit:0 \
+ jail -c name=jail1 persist meta="a b c"
+
+ atf_check -s exit:0 -o inline:"a b c\n" \
+ jls -j jail1 meta
+}
+jail_create_cleanup()
+{
+ jail -r jail1
+ return 0
+}
+
+atf_test_case "jail_modify" "cleanup"
+jail_modify_head()
+{
+ atf_set descr 'Test that meta can be modified after jail creation with jail(8)'
+ atf_set require.user root
+ atf_set execenv jail
+}
+jail_modify_body()
+{
+ setup
+
+ atf_check -s not-exit:0 -e match:"not found" -o ignore \
+ jls -j jail1
+
+ atf_check -s exit:0 \
+ jail -c name=jail1 persist meta="a b c"
+
+ atf_check -s exit:0 -o inline:"a b c\n" \
+ jls -j jail1 meta
+
+ atf_check -s exit:0 \
+ jail -m name=jail1 meta="t1=A t2=B"
+
+ atf_check -s exit:0 -o inline:"t1=A t2=B\n" \
+ jls -j jail1 meta
+}
+jail_modify_cleanup()
+{
+ jail -r jail1
+ return 0
+}
+
+atf_test_case "jail_add" "cleanup"
+jail_add_head()
+{
+ atf_set descr 'Test that meta can be added to an existing jail with jail(8)'
+ atf_set require.user root
+ atf_set execenv jail
+}
+jail_add_body()
+{
+ setup
+
+ atf_check -s not-exit:0 -e match:"not found" -o ignore \
+ jls -j jail1
+
+ atf_check -s exit:0 \
+ jail -c name=jail1 persist host.hostname=jail1
+
+ atf_check -s exit:0 -o inline:'""\n' \
+ jls -j jail1 meta
+
+ atf_check -s exit:0 \
+ jail -m name=jail1 meta="$(jot 3 1 3)"
+
+ atf_check -s exit:0 -o inline:"1\n2\n3\n" \
+ jls -j jail1 meta
+}
+jail_add_cleanup()
+{
+ jail -r jail1
+ return 0
+}
+
+atf_test_case "jail_reset" "cleanup"
+jail_reset_head()
+{
+ atf_set descr 'Test that meta can be reset to an empty string with jail(8)'
+ atf_set require.user root
+ atf_set execenv jail
+}
+jail_reset_body()
+{
+ setup
+
+ atf_check -s not-exit:0 -e match:"not found" -o ignore \
+ jls -j jail1
+
+ atf_check -s exit:0 \
+ jail -c name=jail1 persist meta="123"
+
+ atf_check -s exit:0 -o inline:"123\n" \
+ jls -j jail1 meta
+
+ atf_check -s exit:0 \
+ jail -m name=jail1 meta=
+
+ atf_check -s exit:0 -o inline:'""\n' \
+ jls -j jail1 meta
+}
+jail_reset_cleanup()
+{
+ jail -r jail1
+ return 0
+}
+
+atf_test_case "jls_libxo" "cleanup"
+jls_libxo_head()
+{
+ atf_set descr 'Test that meta can be read with jls(8) using libxo'
+ atf_set require.user root
+ atf_set execenv jail
+}
+jls_libxo_body()
+{
+ setup
+
+ atf_check -s not-exit:0 -e match:"not found" -o ignore \
+ jls -j jail1
+
+ atf_check -s exit:0 \
+ jail -c name=jail1 persist meta="a b c"
+
+ atf_check -s exit:0 -o inline:'{"__version": "2", "jail-information": {"jail": [{"name":"jail1","meta":"a b c"}]}}\n' \
+ jls -j jail1 --libxo json name meta
+}
+jls_libxo_cleanup()
+{
+ jail -r jail1
+ return 0
+}
+
+atf_test_case "flua_create" "cleanup"
+flua_create_head()
+{
+ atf_set descr 'Test that meta can be set upon jail creation with flua'
+ atf_set require.user root
+ atf_set execenv jail
+}
+flua_create_body()
+{
+ setup
+
+ atf_check -s not-exit:0 -e match:"not found" -o ignore \
+ jls -j jail1
+
+ atf_check -s exit:0 \
+ /usr/libexec/flua -ljail -e 'jail.setparams("jail1", {["meta"]="t1 t2=v2", ["persist"]="true"}, jail.CREATE)'
+
+ atf_check -s exit:0 -o inline:"t1 t2=v2\n" \
+ /usr/libexec/flua -ljail -e 'jid, res = jail.getparams("jail1", {"meta"}); print(res["meta"])'
+}
+flua_create_cleanup()
+{
+ jail -r jail1
+ return 0
+}
+
+atf_test_case "flua_modify" "cleanup"
+flua_modify_head()
+{
+ atf_set descr 'Test that meta can be changed with flua after jail creation'
+ atf_set require.user root
+ atf_set execenv jail
+}
+flua_modify_body()
+{
+ setup
+
+ atf_check -s not-exit:0 -e match:"not found" -o ignore \
+ jls -j jail1
+
+ atf_check -s exit:0 \
+ jail -c name=jail1 persist meta="ABC"
+
+ atf_check -s exit:0 -o inline:"ABC\n" \
+ jls -j jail1 meta
+
+ atf_check -s exit:0 \
+ /usr/libexec/flua -ljail -e 'jail.setparams("jail1", {["meta"]="t1 t2=v"}, jail.UPDATE)'
+
+ atf_check -s exit:0 -o inline:"t1 t2=v\n" \
+ jls -j jail1 meta
+}
+flua_modify_cleanup()
+{
+ jail -r jail1
+ return 0
+}
+
+atf_test_case "readable_from_jail" "cleanup"
+readable_from_jail_head()
+{
+ atf_set descr 'Test that a jail can read its own meta parameter via sysctl(8)'
+ atf_set require.user root
+ atf_set execenv jail
+}
+readable_from_jail_body()
+{
+ setup
+
+ atf_check -s not-exit:0 -e match:"not found" -o ignore \
+ jls -j jail1
+
+ atf_check -s exit:0 \
+ jail -c name=jail1 persist meta="a b c"
+
+ atf_check -s exit:0 -o inline:"a b c\n" \
+ jls -j jail1 meta
+
+ atf_check -s exit:0 -o inline:"a b c\n" \
+ jexec jail1 sysctl -n security.jail.meta
+}
+readable_from_jail_cleanup()
+{
+ jail -r jail1
+ return 0
+}
+
+atf_test_case "not_inheritable" "cleanup"
+not_inheritable_head()
+{
+ atf_set descr 'Test that a jail does not inherit meta parameter from its parent jail'
+ atf_set require.user root
+ atf_set execenv jail
+}
+not_inheritable_body()
+{
+ setup
+
+ atf_check -s not-exit:0 -e match:"not found" -o ignore \
+ jls -j parent
+
+ atf_check -s exit:0 \
+ jail -c name=parent children.max=1 persist meta="a b c"
+
+ jexec parent jail -c name=child persist
+
+ atf_check -s exit:0 -o inline:"a b c\n" \
+ jexec parent sysctl -n security.jail.meta
+
+ atf_check -s exit:0 -o inline:"\n" \
+ jexec parent.child sysctl -n security.jail.meta
+}
+not_inheritable_cleanup()
+{
+ jail -r parent.child
+ jail -r parent
+ return 0
+}
+
+atf_test_case "maxbufsize" "cleanup"
+maxbufsize_head()
+{
+ atf_set descr 'Test that meta buffer maximum size can be changed via sysctl from prison0'
+ atf_set require.user root
+}
+maxbufsize_body()
+{
+ setup
+
+ jn=jailmeta_maxbufsize
+
+ atf_check -s not-exit:0 -e match:"not found" -o ignore \
+ jls -j $jn
+
+ # the size counts string length and the trailing \0 char
+ origmax=$(sysctl -n security.jail.meta_maxbufsize)
+
+ # must be fine with current max
+ atf_check -s exit:0 \
+ jail -c name=$jn persist meta="$(printf %$((origmax-1))s)"
+ atf_check -s exit:0 -o inline:"${origmax}\n" \
+ jls -j $jn meta | wc -c
+
+ # should not allow exceeding current max
+ atf_check -s not-exit:0 -e match:"too large" \
+ jail -m name=$jn meta="$(printf %${origmax}s)"
+
+ # should allow the same size with increased max
+ newmax=$((origmax + 1))
+ sysctl security.jail.meta_maxbufsize=$newmax
+ atf_check -s exit:0 \
+ jail -m name=$jn meta="$(printf %${origmax}s)"
+ atf_check -s exit:0 -o inline:"${origmax}\n" \
+ jls -j $jn meta | wc -c
+
+ # decrease back to the original max
+ sysctl security.jail.meta_maxbufsize=$origmax
+ atf_check -s not-exit:0 -e match:"too large" \
+ jail -m name=$jn meta="$(printf %${origmax}s)"
+
+ # the previously set long meta is still readable as is
+ # due to the soft limit remains higher than the hard limit
+ atf_check_equal "${newmax}" "$(sysctl -n security.jail.param.meta)"
+ atf_check -s exit:0 -o inline:"${origmax}\n" \
+ jls -j $jn meta | wc -c
+}
+maxbufsize_cleanup()
+{
+ jail -r jailmeta_maxbufsize
+ return 0
+}
+
+atf_init_test_cases()
+{
+ atf_add_test_case "jail_create"
+ atf_add_test_case "jail_modify"
+ atf_add_test_case "jail_add"
+ atf_add_test_case "jail_reset"
+
+ atf_add_test_case "jls_libxo"
+
+ atf_add_test_case "flua_create"
+ atf_add_test_case "flua_modify"
+
+ atf_add_test_case "readable_from_jail"
+ atf_add_test_case "not_inheritable"
+
+ atf_add_test_case "maxbufsize"
+}
diff --git a/usr.sbin/jail/jail.8 b/usr.sbin/jail/jail.8
--- a/usr.sbin/jail/jail.8
+++ b/usr.sbin/jail/jail.8
@@ -507,6 +507,11 @@
The number for the jail's
.Va kern.osreldate
and uname -K.
+.It meta
+Any string associated with the jail.
+Its buffer size is limited by the global
+.Va security.jail.meta_maxbufsize
+sysctl, which can only be tuned by the non-jailed root user.
.It Va allow.*
Some restrictions of the jail environment may be set on a per-jail
basis.

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