Kernel: Clarify ambiguous {File,Description}::absolute_path

Found due to smelly code in InodeFile::absolute_path.

In particular, this replaces the following misleading methods:

File::absolute_path
This method *never* returns an actual path, and if called on an
InodeFile (which is impossible), it would VERIFY_NOT_REACHED().

OpenFileDescription::try_serialize_absolute_path
OpenFileDescription::absolute_path
These methods do not guarantee to return an actual path (just like the
other method), and just like Custody::absolute_path they do not
guarantee accuracy. In particular, just renaming the method made a
TOCTOU bug obvious.

The new method signatures use KResultOr, just like
try_serialize_absolute_path() already did.

Kernel/Devices/Device.cpp

@@ -140,18 +140,9 @@ Device::~Device()
     VERIFY(m_state == State::BeingRemoved);
 }
 
-String Device::absolute_path() const
+KResultOr<NonnullOwnPtr<KString>> Device::pseudo_path(const OpenFileDescription&) const
 {
-    // FIXME: I assume we can't really provide a well known path in the kernel
-    // because this is a violation of abstraction layers between userland and the
-    // kernel, but maybe the whole name of "absolute_path" is just wrong as this
-    // is really not an "absolute_path".
-    return String::formatted("device:{},{}", major(), minor());
-}
-
-String Device::absolute_path(const OpenFileDescription&) const
-{
-    return absolute_path();
+    return KString::try_create(String::formatted("device:{},{}", major(), minor()));
 }
 
 void Device::process_next_queued_request(Badge<AsyncDeviceRequest>, const AsyncDeviceRequest& completed_request)

Kernel/Devices/Device.h

@@ -40,8 +40,7 @@ public:
     unsigned major() const { return m_major; }
     unsigned minor() const { return m_minor; }
 
-    virtual String absolute_path(const OpenFileDescription&) const override;
-    virtual String absolute_path() const;
+    virtual KResultOr<NonnullOwnPtr<KString>> pseudo_path(const OpenFileDescription&) const override;
 
     UserID uid() const { return m_uid; }
     GroupID gid() const { return m_gid; }

Kernel/FileSystem/AnonymousFile.cpp

@@ -30,4 +30,9 @@ KResultOr<Memory::Region*> AnonymousFile::mmap(Process& process, OpenFileDescrip
     return process.address_space().allocate_region_with_vmobject(range, m_vmobject, offset, {}, prot, shared);
 }
 
+KResultOr<NonnullOwnPtr<KString>> AnonymousFile::pseudo_path(const OpenFileDescription&) const
+{
+    return KString::try_create(":anonymous-file:"sv);
+}
+
 }

Kernel/FileSystem/AnonymousFile.h

@@ -24,7 +24,7 @@ public:
 
 private:
     virtual StringView class_name() const override { return "AnonymousFile"sv; }
-    virtual String absolute_path(const OpenFileDescription&) const override { return ":anonymous-file:"; }
+    virtual KResultOr<NonnullOwnPtr<KString>> pseudo_path(const OpenFileDescription&) const;
     virtual bool can_read(const OpenFileDescription&, size_t) const override { return false; }
     virtual bool can_write(const OpenFileDescription&, size_t) const override { return false; }
     virtual KResultOr<size_t> read(OpenFileDescription&, u64, UserOrKernelBuffer&, size_t) override { return ENOTSUP; }

Kernel/FileSystem/FIFO.cpp

@@ -132,9 +132,9 @@ KResultOr<size_t> FIFO::write(OpenFileDescription& fd, u64, const UserOrKernelBu
     return m_buffer->write(buffer, size);
 }
 
-String FIFO::absolute_path(const OpenFileDescription&) const
+KResultOr<NonnullOwnPtr<KString>> FIFO::pseudo_path(const OpenFileDescription&) const
 {
-    return String::formatted("fifo:{}", m_fifo_id);
+    return KString::try_create(String::formatted("fifo:{}", m_fifo_id));
 }
 
 KResult FIFO::stat(::stat& st) const

Kernel/FileSystem/FIFO.h

@@ -45,7 +45,7 @@ private:
     virtual KResult stat(::stat&) const override;
     virtual bool can_read(const OpenFileDescription&, size_t) const override;
     virtual bool can_write(const OpenFileDescription&, size_t) const override;
-    virtual String absolute_path(const OpenFileDescription&) const override;
+    virtual KResultOr<NonnullOwnPtr<KString>> pseudo_path(const OpenFileDescription&) const override;
     virtual StringView class_name() const override { return "FIFO"sv; }
     virtual bool is_fifo() const override { return true; }
 

Kernel/FileSystem/File.h

@@ -93,7 +93,8 @@ public:
     virtual KResultOr<Memory::Region*> mmap(Process&, OpenFileDescription&, Memory::VirtualRange const&, u64 offset, int prot, bool shared);
     virtual KResult stat(::stat&) const { return EBADF; }
 
-    virtual String absolute_path(const OpenFileDescription&) const = 0;
+    // Although this might be better described "name" or "description", these terms already have other meanings.
+    virtual KResultOr<NonnullOwnPtr<KString>> pseudo_path(const OpenFileDescription&) const = 0;
 
     virtual KResult truncate(u64) { return EINVAL; }
     virtual KResult sync() { return EINVAL; }

Kernel/FileSystem/InodeFile.cpp

@@ -89,15 +89,14 @@ KResultOr<Memory::Region*> InodeFile::mmap(Process& process, OpenFileDescription
         vmobject = TRY(Memory::SharedInodeVMObject::try_create_with_inode(inode()));
     else
         vmobject = TRY(Memory::PrivateInodeVMObject::try_create_with_inode(inode()));
-    auto path = TRY(description.try_serialize_absolute_path());
+    auto path = TRY(description.pseudo_path());
     return process.address_space().allocate_region_with_vmobject(range, vmobject.release_nonnull(), offset, path->view(), prot, shared);
 }
 
-String InodeFile::absolute_path(const OpenFileDescription& description) const
+KResultOr<NonnullOwnPtr<KString>> InodeFile::pseudo_path(const OpenFileDescription&) const
 {
+    // If it has an inode, then it has a path, and therefore the caller should have been able to get a custody at some point.
     VERIFY_NOT_REACHED();
-    VERIFY(description.custody());
-    return description.absolute_path();
 }
 
 KResult InodeFile::truncate(u64 size)

Kernel/FileSystem/InodeFile.h

@@ -36,7 +36,7 @@ public:
     virtual KResultOr<Memory::Region*> mmap(Process&, OpenFileDescription&, Memory::VirtualRange const&, u64 offset, int prot, bool shared) override;
     virtual KResult stat(::stat& buffer) const override { return inode().metadata().stat(buffer); }
 
-    virtual String absolute_path(const OpenFileDescription&) const override;
+    virtual KResultOr<NonnullOwnPtr<KString>> pseudo_path(const OpenFileDescription&) const override;
 
     virtual KResult truncate(u64) override;
     virtual KResult sync() override;

Kernel/FileSystem/InodeWatcher.cpp

@@ -81,9 +81,9 @@ KResult InodeWatcher::close()
     return KSuccess;
 }
 
-String InodeWatcher::absolute_path(const OpenFileDescription&) const
+KResultOr<NonnullOwnPtr<KString>> InodeWatcher::pseudo_path(const OpenFileDescription&) const
 {
-    return String::formatted("InodeWatcher:({})", m_wd_to_watches.size());
+    return KString::try_create(String::formatted("InodeWatcher:({})", m_wd_to_watches.size()));
 }
 
 void InodeWatcher::notify_inode_event(Badge<Inode>, InodeIdentifier inode_id, InodeWatcherEvent::Type event_type, String const& name)

Kernel/FileSystem/InodeWatcher.h

@@ -50,7 +50,7 @@ public:
     virtual KResultOr<size_t> write(OpenFileDescription&, u64, const UserOrKernelBuffer&, size_t) override { return EIO; }
     virtual KResult close() override;
 
-    virtual String absolute_path(const OpenFileDescription&) const override;
+    virtual KResultOr<NonnullOwnPtr<KString>> pseudo_path(const OpenFileDescription&) const override;
     virtual StringView class_name() const override { return "InodeWatcher"sv; };
     virtual bool is_inode_watcher() const override { return true; }
 

Kernel/FileSystem/OpenFileDescription.cpp

@@ -349,19 +349,18 @@ KResult OpenFileDescription::close()
     return m_file->close();
 }
 
-KResultOr<NonnullOwnPtr<KString>> OpenFileDescription::try_serialize_absolute_path()
+KResultOr<NonnullOwnPtr<KString>> OpenFileDescription::original_absolute_path() const
 {
-    if (m_custody)
-        return m_custody->try_serialize_absolute_path();
-    // FIXME: Don't go through a String here!
-    return KString::try_create(m_file->absolute_path(*this));
+    if (!m_custody)
+        return ENOENT;
+    return m_custody->try_serialize_absolute_path();
 }
 
-String OpenFileDescription::absolute_path() const
+KResultOr<NonnullOwnPtr<KString>> OpenFileDescription::pseudo_path() const
 {
     if (m_custody)
-        return m_custody->absolute_path();
-    return m_file->absolute_path(*this);
+        return m_custody->try_serialize_absolute_path();
+    return m_file->pseudo_path(*this);
 }
 
 InodeMetadata OpenFileDescription::metadata() const

Kernel/FileSystem/OpenFileDescription.h

@@ -64,8 +64,8 @@ public:
 
     KResultOr<NonnullOwnPtr<KBuffer>> read_entire_file();
 
-    KResultOr<NonnullOwnPtr<KString>> try_serialize_absolute_path();
-    String absolute_path() const;
+    KResultOr<NonnullOwnPtr<KString>> original_absolute_path() const;
+    KResultOr<NonnullOwnPtr<KString>> pseudo_path() const;
 
     bool is_direct() const { return m_direct; }
 

Kernel/FileSystem/VirtualFileSystem.cpp

@@ -124,7 +124,8 @@ KResult VirtualFileSystem::mount_root(FileSystem& fs)
     }
 
     m_root_inode = root_inode;
-    dmesgln("VirtualFileSystem: mounted root from {} ({})", fs.class_name(), static_cast<FileBackedFileSystem&>(fs).file_description().absolute_path());
+    auto pseudo_path = TRY(static_cast<FileBackedFileSystem&>(fs).file_description().pseudo_path());
+    dmesgln("VirtualFileSystem: mounted root from {} ({})", fs.class_name(), pseudo_path);
 
     m_mounts.with_exclusive([&](auto& mounts) {
         mounts.append(move(mount));

Kernel/GlobalProcessExposed.cpp

@@ -365,15 +365,23 @@ private:
             fs_object.add("readonly", fs.is_readonly());
             fs_object.add("mount_flags", mount.flags());
 
-            if (fs.is_file_backed())
-                fs_object.add("source", static_cast<const FileBackedFileSystem&>(fs).file_description().absolute_path());
-            else
+            if (fs.is_file_backed()) {
+                auto pseudo_path_or_error = static_cast<const FileBackedFileSystem&>(fs).file_description().pseudo_path();
+                if (pseudo_path_or_error.is_error()) {
+                    // We're probably out of memory and should not attempt to continue.
+                    result = pseudo_path_or_error.error();
+                    return IterationDecision::Break;
+                }
+                fs_object.add("source", pseudo_path_or_error.value()->characters());
+            } else {
                 fs_object.add("source", "none");
+            }
 
             return IterationDecision::Continue;
         });
-        array.finish();
-        return KSuccess;
+        if (result == KSuccess)
+            array.finish();
+        return result;
     }
 };
 

Kernel/Net/IPv4Socket.cpp

@@ -456,10 +456,10 @@ bool IPv4Socket::did_receive(const IPv4Address& source_address, u16 source_port,
     return true;
 }
 
-String IPv4Socket::absolute_path(const OpenFileDescription&) const
+KResultOr<NonnullOwnPtr<KString>> IPv4Socket::pseudo_path(const OpenFileDescription&) const
 {
     if (m_role == Role::None)
-        return "socket";
+        return KString::try_create("socket"sv);
 
     StringBuilder builder;
     builder.append("socket:");
@@ -485,7 +485,7 @@ String IPv4Socket::absolute_path(const OpenFileDescription&) const
         VERIFY_NOT_REACHED();
     }
 
-    return builder.to_string();
+    return KString::try_create(builder.to_string());
 }
 
 KResult IPv4Socket::setsockopt(int level, int option, Userspace<const void*> user_value, socklen_t user_value_size)

Kernel/Net/IPv4Socket.h

@@ -61,7 +61,7 @@ public:
 
     IPv4SocketTuple tuple() const { return IPv4SocketTuple(m_local_address, m_local_port, m_peer_address, m_peer_port); }
 
-    String absolute_path(const OpenFileDescription& description) const override;
+    KResultOr<NonnullOwnPtr<KString>> pseudo_path(const OpenFileDescription& description) const override;
 
     u8 type_of_service() const { return m_type_of_service; }
     u8 ttl() const { return m_ttl; }

Kernel/Net/LocalSocket.cpp

@@ -355,7 +355,7 @@ StringView LocalSocket::socket_path() const
     return m_path->view();
 }
 
-String LocalSocket::absolute_path(const OpenFileDescription& description) const
+KResultOr<NonnullOwnPtr<KString>> LocalSocket::pseudo_path(const OpenFileDescription& description) const
 {
     StringBuilder builder;
     builder.append("socket:");
@@ -378,7 +378,7 @@ String LocalSocket::absolute_path(const OpenFileDescription& description) const
         break;
     }
 
-    return builder.to_string();
+    return KString::try_create(builder.to_string());
 }
 
 KResult LocalSocket::getsockopt(OpenFileDescription& description, int level, int option, Userspace<void*> value, Userspace<socklen_t*> value_size)

Kernel/Net/LocalSocket.h

@@ -32,7 +32,7 @@ public:
     static void for_each(Function<void(const LocalSocket&)>);
 
     StringView socket_path() const;
-    String absolute_path(const OpenFileDescription& description) const override;
+    KResultOr<NonnullOwnPtr<KString>> pseudo_path(const OpenFileDescription& description) const override;
 
     // ^Socket
     virtual KResult bind(Userspace<const sockaddr*>, socklen_t) override;

Kernel/Net/Socket.h

@@ -105,7 +105,7 @@ public:
     virtual KResultOr<size_t> read(OpenFileDescription&, u64, UserOrKernelBuffer&, size_t) override final;
     virtual KResultOr<size_t> write(OpenFileDescription&, u64, const UserOrKernelBuffer&, size_t) override final;
     virtual KResult stat(::stat&) const override;
-    virtual String absolute_path(const OpenFileDescription&) const override = 0;
+    virtual KResultOr<NonnullOwnPtr<KString>> pseudo_path(const OpenFileDescription&) const override = 0;
 
     bool has_receive_timeout() const { return m_receive_timeout != Time::zero(); }
     const Time& receive_timeout() const { return m_receive_timeout; }

Kernel/ProcessSpecificExposed.cpp

@@ -80,9 +80,10 @@ KResultOr<NonnullRefPtr<Inode>> Process::lookup_stacks_directory(const ProcFS& p
 KResultOr<size_t> Process::procfs_get_file_description_link(unsigned fd, KBufferBuilder& builder) const
 {
     auto file_description = TRY(m_fds.open_file_description(fd));
-    auto data = file_description->absolute_path();
-    TRY(builder.append(data));
-    return data.length();
+    // Note: These links are not guaranteed to point to actual VFS paths, just like in other kernels.
+    auto data = TRY(file_description->pseudo_path());
+    TRY(builder.append(data->view()));
+    return data->length();
 }
 
 KResult Process::traverse_file_descriptions_directory(unsigned fsid, Function<bool(FileSystem::DirectoryEntryView const&)> callback) const
@@ -187,7 +188,9 @@ KResult Process::procfs_get_fds_stats(KBufferBuilder& builder) const
         RefPtr<OpenFileDescription> description = file_description_metadata.description();
         auto description_object = array.add_object();
         description_object.add("fd", count);
-        description_object.add("absolute_path", description->absolute_path());
+        // TODO: Better OOM handling.
+        auto pseudo_path_or_error = description->pseudo_path();
+        description_object.add("absolute_path", pseudo_path_or_error.is_error() ? "???"sv : pseudo_path_or_error.value()->view());
         description_object.add("seekable", description->file().is_seekable());
         description_object.add("class", description->file().class_name());
         description_object.add("offset", description->offset());

Kernel/Syscalls/execve.cpp

@@ -275,7 +275,7 @@ static KResultOr<LoadResult> load_elf_object(NonnullOwnPtr<Memory::AddressSpace>
     size_t master_tls_alignment = 0;
     FlatPtr load_base_address = 0;
 
-    auto elf_name = TRY(object_description.try_serialize_absolute_path());
+    auto elf_name = TRY(object_description.pseudo_path());
     VERIFY(!Processor::in_critical());
 
     Memory::MemoryManager::enter_address_space(*new_space);
@@ -438,7 +438,9 @@ KResult Process::do_exec(NonnullRefPtr<OpenFileDescription> main_program_descrip
 {
     VERIFY(is_user_process());
     VERIFY(!Processor::in_critical());
-    auto path = TRY(main_program_description->try_serialize_absolute_path());
+    // Although we *could* handle a pseudo_path here, trying to execute something that doesn't have
+    // a custody (e.g. BlockDevice or RandomDevice) is pretty suspicious anyway.
+    auto path = TRY(main_program_description->original_absolute_path());
 
     dbgln_if(EXEC_DEBUG, "do_exec: {}", path);
 

Kernel/Syscalls/mount.cpp

@@ -70,7 +70,8 @@ KResultOr<FlatPtr> Process::sys$mount(Userspace<const Syscall::SC_mount_params*>
             return ENODEV;
         }
 
-        dbgln("mount: attempting to mount {} on {}", description->absolute_path(), target);
+        auto source_pseudo_path = TRY(description->pseudo_path());
+        dbgln("mount: attempting to mount {} on {}", source_pseudo_path, target);
 
         fs = TRY(Ext2FS::try_create(*description));
     } else if (fs_type == "9p"sv || fs_type == "Plan9FS"sv) {
@@ -96,7 +97,8 @@ KResultOr<FlatPtr> Process::sys$mount(Userspace<const Syscall::SC_mount_params*>
             dbgln("mount: this is not a seekable file");
             return ENODEV;
         }
-        dbgln("mount: attempting to mount {} on {}", description->absolute_path(), target);
+        auto source_pseudo_path = TRY(description->pseudo_path());
+        dbgln("mount: attempting to mount {} on {}", source_pseudo_path, target);
         fs = TRY(ISO9660FS::try_create(*description));
     } else {
         return ENODEV;

Kernel/Syscalls/statvfs.cpp

@@ -77,7 +77,9 @@ KResultOr<FlatPtr> Process::sys$fstatvfs(int fd, statvfs* buf)
     REQUIRE_PROMISE(stdio);
 
     auto description = TRY(fds().open_file_description(fd));
-    return do_statvfs(description->absolute_path(), buf);
+    auto absolute_path = TRY(description->original_absolute_path());
+    // FIXME: TOCTOU bug! The file connected to the fd may or may not have been moved, and the name possibly taken by a different file.
+    return do_statvfs(absolute_path->view(), buf);
 }
 
 }

Kernel/TTY/MasterPTY.cpp

@@ -127,9 +127,10 @@ KResult MasterPTY::ioctl(OpenFileDescription& description, unsigned request, Use
     return EINVAL;
 }
 
-String MasterPTY::absolute_path(const OpenFileDescription&) const
+KResultOr<NonnullOwnPtr<KString>> MasterPTY::pseudo_path(const OpenFileDescription&) const
 {
-    return String::formatted("ptm:{}", m_pts_name);
+    // FIXME: Replace this and others of this pattern by KString::formatted()
+    return KString::try_create(String::formatted("ptm:{}", m_pts_name));
 }
 
 }

Kernel/TTY/MasterPTY.h

@@ -26,7 +26,7 @@ public:
     void notify_slave_closed(Badge<SlavePTY>);
     bool is_closed() const { return m_closed; }
 
-    virtual String absolute_path(const OpenFileDescription&) const override;
+    virtual KResultOr<NonnullOwnPtr<KString>> pseudo_path(const OpenFileDescription&) const override;
 
 private:
     explicit MasterPTY(unsigned index, NonnullOwnPtr<DoubleBuffer> buffer);

Kernel/TTY/TTY.cpp

@@ -576,6 +576,11 @@ KResult TTY::ioctl(OpenFileDescription&, unsigned request, Userspace<void*> arg)
     return EINVAL;
 }
 
+KResultOr<NonnullOwnPtr<KString>> TTY::pseudo_path(const OpenFileDescription&) const
+{
+    return KString::try_create(tty_name());
+}
+
 void TTY::set_size(unsigned short columns, unsigned short rows)
 {
     m_rows = rows;

Kernel/TTY/TTY.h

@@ -26,7 +26,7 @@ public:
     virtual bool can_read(const OpenFileDescription&, size_t) const override;
     virtual bool can_write(const OpenFileDescription&, size_t) const override;
     virtual KResult ioctl(OpenFileDescription&, unsigned request, Userspace<void*> arg) override final;
-    virtual String absolute_path(const OpenFileDescription&) const override { return tty_name(); }
+    virtual KResultOr<NonnullOwnPtr<KString>> pseudo_path(const OpenFileDescription&) const override;
 
     virtual String const& tty_name() const = 0;