Kernel: Allow configuring a Jail to not impose PID isolation restriction

This is quite useful for userspace applications that can't cope with the
restriction, but it's still useful to impose other non-configurable
restrictions by using jails.

Base/usr/share/man/man1/jail-create.md

@@ -12,9 +12,16 @@ $ jail-create <name>
 
 `jail-create` creates a new jail, with a specified name
 
+## Options
+
+* `-p`, `--pid-isolation`: Use PID-isolation (as a custom isolation option)
+
 ## Examples
 
 ```sh
-# Create jail with the name "test-jail"
+# Create jail with the name "test-jail", with no PID isolation
 $ jail-create test-jail
+
+# Create jail with the name "test-jail", with PID isolation
+$ jail-create -p test-jail
 ```

Base/usr/share/man/man7/Mitigations.md

@@ -95,7 +95,7 @@ Kernel: Add a basic implementation of unveil()
 `jails` are mitigation originating from FreeBSD.
 It allows a program to be placed inside a lightweight OS-level virtualization environment.
 
-Current restrictions on jailed processes:
+Current restrictions on jailed processes (configurable when creating a Jail):
 - Process ID view isolation, being limited (both in `/proc` and `/sys/kernel/processes`) to only processes that share the same jail.
 
 Special restrictions on filesystem also apply:

Kernel/API/Jail.h

@@ -0,0 +1,17 @@
+/*
+ * Copyright (c) 2022, Liav A. <liavalb@hotmail.co.il>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/EnumBits.h>
+#include <AK/Types.h>
+
+enum class JailIsolationFlags : u32 {
+    None = 0,
+    PIDIsolation = 1 << 0,
+};
+
+AK_ENUM_BITWISE_OPERATORS(JailIsolationFlags);

Kernel/API/Syscall.h

@@ -343,6 +343,7 @@ struct SC_setkeymap_params {
 struct SC_jail_create_params {
     u64 index;
     StringArgument name;
+    int flags;
 };
 
 struct SC_jail_attach_params {

Kernel/Jail.cpp

@@ -6,6 +6,7 @@
 
 #include <AK/IntrusiveList.h>
 #include <AK/Singleton.h>
+#include <Kernel/API/Jail.h>
 #include <Kernel/Jail.h>
 #include <Kernel/Process.h>
 
@@ -19,16 +20,19 @@ static JailIndex generate_jail_id()
     return s_jail_id.fetch_add(1);
 }
 
-NonnullRefPtr<ProcessList> Jail::process_list()
+RefPtr<ProcessList> Jail::process_list()
 {
     return m_process_list;
 }
 
-ErrorOr<NonnullRefPtr<Jail>> Jail::create(NonnullOwnPtr<KString> name)
+ErrorOr<NonnullRefPtr<Jail>> Jail::create(NonnullOwnPtr<KString> name, unsigned flags)
 {
+    RefPtr<ProcessList> jail_process_list;
+    if (flags & static_cast<unsigned>(JailIsolationFlags::PIDIsolation))
+        jail_process_list = TRY(ProcessList::create());
+
     return s_all_instances->with([&](auto& list) -> ErrorOr<NonnullRefPtr<Jail>> {
-        auto process_list = TRY(ProcessList::create());
+        auto jail = TRY(adopt_nonnull_ref_or_enomem(new (nothrow) Jail(move(name), generate_jail_id(), jail_process_list)));
-        auto jail = TRY(adopt_nonnull_ref_or_enomem(new (nothrow) Jail(move(name), generate_jail_id(), move(process_list))));
         list.append(jail);
         return jail;
     });
@@ -61,10 +65,10 @@ RefPtr<Jail> Jail::find_by_index(JailIndex index)
     });
 }
 
-Jail::Jail(NonnullOwnPtr<KString> name, JailIndex index, NonnullRefPtr<ProcessList> process_list)
+Jail::Jail(NonnullOwnPtr<KString> name, JailIndex index, RefPtr<ProcessList> process_list)
     : m_name(move(name))
     , m_index(index)
-    , m_process_list(move(process_list))
+    , m_process_list(process_list)
 {
 }
 

Kernel/Jail.h

@@ -28,10 +28,10 @@ AK_TYPEDEF_DISTINCT_ORDERED_ID(u64, JailIndex);
 class Jail : public AtomicRefCounted<Jail> {
 
 public:
-    NonnullRefPtr<ProcessList> process_list();
+    RefPtr<ProcessList> process_list();
 
     static RefPtr<Jail> find_by_index(JailIndex);
-    static ErrorOr<NonnullRefPtr<Jail>> create(NonnullOwnPtr<KString> name);
+    static ErrorOr<NonnullRefPtr<Jail>> create(NonnullOwnPtr<KString> name, unsigned flags);
     static ErrorOr<void> for_each_when_process_is_not_jailed(Function<ErrorOr<void>(Jail const&)> callback);
 
     StringView name() const { return m_name->view(); }
@@ -41,7 +41,7 @@ public:
     SpinlockProtected<size_t, LockRank::None>& attach_count() { return m_attach_count; }
 
 private:
-    Jail(NonnullOwnPtr<KString>, JailIndex, NonnullRefPtr<ProcessList>);
+    Jail(NonnullOwnPtr<KString>, JailIndex, RefPtr<ProcessList>);
 
     NonnullOwnPtr<KString> m_name;
     JailIndex const m_index;
@@ -52,7 +52,7 @@ public:
     using List = IntrusiveListRelaxedConst<&Jail::m_list_node>;
 
 private:
-    NonnullRefPtr<ProcessList> const m_process_list;
+    RefPtr<ProcessList> const m_process_list;
 
     SpinlockProtected<size_t, LockRank::None> m_attach_count { 0 };
 };

Kernel/Syscalls/jail.cpp

@@ -5,7 +5,7 @@
  */
 
 #include <AK/Userspace.h>
-#include <Kernel/API/Ioctl.h>
+#include <Kernel/API/Jail.h>
 #include <Kernel/Jail.h>
 #include <Kernel/Process.h>
 #include <Kernel/StdLib.h>
@@ -30,7 +30,7 @@ ErrorOr<FlatPtr> Process::sys$jail_create(Userspace<Syscall::SC_jail_create_para
         // any info leak about the "outside world" jail metadata.
         if (my_jail)
             return Error::from_errno(EPERM);
-        auto jail = TRY(Jail::create(move(jail_name)));
+        auto jail = TRY(Jail::create(move(jail_name), static_cast<unsigned>(params.flags)));
         return jail->index().value();
     }));
     // Note: We do the copy_to_user outside of the m_attached_jail Spinlock locked scope because

Userland/Libraries/LibCore/System.cpp

@@ -1172,9 +1172,9 @@ ErrorOr<void> join_jail(u64 jail_index)
     HANDLE_SYSCALL_RETURN_VALUE("jail_attach", rc, {});
 }
 
-ErrorOr<u64> create_jail(StringView jail_name)
+ErrorOr<u64> create_jail(StringView jail_name, JailIsolationFlags flags)
 {
-    Syscall::SC_jail_create_params params { 0, { jail_name.characters_without_null_termination(), jail_name.length() } };
+    Syscall::SC_jail_create_params params { 0, { jail_name.characters_without_null_termination(), jail_name.length() }, static_cast<int>(flags) };
     int rc = syscall(SC_jail_create, &params);
     HANDLE_SYSCALL_RETURN_VALUE("jail_create", rc, static_cast<u64>(params.index));
 }

Userland/Libraries/LibCore/System.h

@@ -31,6 +31,10 @@
 #include <time.h>
 #include <utime.h>
 
+#ifdef AK_OS_SERENITY
+#    include <Kernel/API/Jail.h>
+#endif
+
 #if !defined(AK_OS_BSD_GENERIC) && !defined(AK_OS_ANDROID)
 #    include <shadow.h>
 #endif
@@ -191,7 +195,7 @@ ErrorOr<void> exec(StringView filename, ReadonlySpan<StringView> arguments, Sear
 
 #ifdef AK_OS_SERENITY
 ErrorOr<void> join_jail(u64 jail_index);
-ErrorOr<u64> create_jail(StringView jail_name);
+ErrorOr<u64> create_jail(StringView jail_name, JailIsolationFlags);
 #endif
 
 ErrorOr<int> socket(int domain, int type, int protocol);

Userland/Utilities/jail-attach.cpp

@@ -31,7 +31,9 @@ ErrorOr<int> serenity_main(Main::Arguments arguments)
     if (existing_jail_index.has_value()) {
         TRY(Core::System::join_jail(existing_jail_index.value()));
     } else {
-        u64 new_jail_index = TRY(Core::System::create_jail(new_jail_name.is_null() ? ""sv : new_jail_name));
+        // NOTE: We create a jail with "default" isolation options (as we define them in this program)
+        JailIsolationFlags default_flags = (JailIsolationFlags::PIDIsolation);
+        u64 new_jail_index = TRY(Core::System::create_jail(new_jail_name.is_null() ? ""sv : new_jail_name, default_flags));
         TRY(Core::System::join_jail(new_jail_index));
     }
     TRY(Core::System::exec_command(command, preserve_env));

Userland/Utilities/jail-create.cpp

@@ -13,15 +13,19 @@ ErrorOr<int> serenity_main(Main::Arguments arguments)
 {
     StringView new_jail_name;
     Core::ArgsParser args_parser;
+    bool pid_isolation = false;
     args_parser.add_positional_argument(new_jail_name, "New jail name", "jail name");
+    args_parser.add_option(pid_isolation, "Use PID-isolation (as a custom isolation option)", "pid-isolation", 'p');
     args_parser.parse(arguments);
 
     TRY(Core::System::pledge("stdio jail"));
 
-    if (!new_jail_name.is_null() && !new_jail_name.is_empty()) {
+    if (new_jail_name.is_null() || new_jail_name.is_empty())
-        TRY(Core::System::create_jail(new_jail_name));
+        return Error::from_string_view("Can't create a jail with empty name."sv);
-        return 0;
-    }
 
-    return Error::from_string_view("Can't create a jail with empty name."sv);
+    JailIsolationFlags flags = JailIsolationFlags::None;
+    if (pid_isolation)
+        flags |= JailIsolationFlags::PIDIsolation;
+    TRY(Core::System::create_jail(new_jail_name, flags));
+    return 0;
 }