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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
@@ -251,6 +251,8 @@
#ifdef AUDIT
{"allow.setaudit", "allow.nosetaudit", PR_ALLOW_SETAUDIT},
#endif
+ {"allow.mount.unsafe.all", "allow.mount.unsafe.noall",
+ PR_ALLOW_MOUNT_UNSAFE_ANY},
};
static unsigned pr_allow_all = PR_ALLOW_ALL_STATIC;
const size_t pr_flag_allow_size = sizeof(pr_flag_allow);
@@ -5243,6 +5245,10 @@
SYSCTL_JAIL_PARAM_SUBNODE(allow, mount, "Jail mount/unmount permission flags");
SYSCTL_JAIL_PARAM(_allow_mount, , CTLTYPE_INT | CTLFLAG_RW,
"B", "Jail may mount/unmount jail-friendly file systems in general");
+SYSCTL_JAIL_PARAM_SUBNODE(allow_mount, unsafe,
+ "Jail unsafe mount/unmount permission flags");
+SYSCTL_JAIL_PARAM(_allow_mount_unsafe, all, CTLTYPE_INT | CTLFLAG_RW,
+ "B", "Jail may mount/unmount any file system (unsafe)");
/*
* Add a dynamic parameter allow.<name>, or allow.<prefix>.<name>. Return
diff --git a/sys/kern/vfs_mount.c b/sys/kern/vfs_mount.c
--- a/sys/kern/vfs_mount.c
+++ b/sys/kern/vfs_mount.c
@@ -1138,8 +1138,9 @@
* If the jail of the calling thread lacks permission for this type of
* file system, or is trying to cover its own root, deny immediately.
*/
- if (jailed(td->td_ucred) && (!prison_allow(td->td_ucred,
- vfsp->vfc_prison_flag) || vp == td->td_ucred->cr_prison->pr_root)) {
+ if (jailed(td->td_ucred) && ((!prison_allow(td->td_ucred,
+ PR_ALLOW_MOUNT_UNSAFE_ANY) && !prison_allow(td->td_ucred,
+ vfsp->vfc_prison_flag)) || vp == td->td_ucred->cr_prison->pr_root)) {
vput(vp);
vfs_unref_vfsconf(vfsp);
return (EPERM);
diff --git a/sys/sys/jail.h b/sys/sys/jail.h
--- a/sys/sys/jail.h
+++ b/sys/sys/jail.h
@@ -273,6 +273,7 @@
#define PR_ALLOW_ROUTING 0x00200000
#define PR_ALLOW_UNPRIV_PARENT_TAMPER 0x00400000
#define PR_ALLOW_SETAUDIT 0x00800000
+#define PR_ALLOW_MOUNT_UNSAFE_ANY 0x01000000
/*
* PR_ALLOW_PRISON0 are the allow flags that we apply by default to prison0,
@@ -280,7 +281,7 @@
* build time. PR_ALLOW_ALL_STATIC should contain any bit above that we expect
* to be used on the system, while PR_ALLOW_PRISON0 will be some subset of that.
*/
-#define PR_ALLOW_ALL_STATIC 0x00ff87ff
+#define PR_ALLOW_ALL_STATIC 0x01ff87ff
#define PR_ALLOW_PRISON0 \
(PR_ALLOW_ALL_STATIC & ~(PR_ALLOW_UNPRIV_PARENT_TAMPER))
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
@@ -827,6 +827,21 @@
.Xr zfs-jail 8
for information on how to configure the ZFS filesystem to operate from
within a jail.
+.It Va allow.mount.unsafe.all
+privileged users inside the jail will be able to mount and unmount
+any file system, regardless of whether it is marked as jail-friendly.
+This permission is effective only together with
+.Va allow.mount
+and only when
+.Va enforce_statfs
+is set to a value lower than 2.
+Many file systems trust the on-disk format and are not hardened against
+malicious input.
+A jailed user who controls the backing image could craft a corrupted
+file system that may trigger kernel panics or arbitrary kernel memory
+access when mounted.
+This option should only be used in environments where the jail's root
+user is fully trusted, such as build jails or development environments.
.It Va allow.vmm
The jail may access
.Xr vmm 4 .

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