Kernel: Fix /proc/<pid>/exe permissions

kernel/include/kernel/FS/ProcFS/Inode.h

@@ -57,6 +57,35 @@ namespace Kernel
 		size_t (Process::*m_callback)(off_t, BAN::ByteSpan) const;
 	};
 
+	class ProcSymlinkProcessInode final : public TmpInode
+	{
+	public:
+		static BAN::ErrorOr<BAN::RefPtr<ProcSymlinkProcessInode>> create_new(Process& process, BAN::ErrorOr<BAN::String> (Process::*callback)() const, TmpFileSystem&, mode_t);
+		~ProcSymlinkProcessInode() = default;
+
+		virtual uid_t uid() const override { return m_process.credentials().ruid(); }
+		virtual gid_t gid() const override { return m_process.credentials().rgid(); }
+
+	protected:
+		virtual BAN::ErrorOr<BAN::String> link_target_impl() override;
+
+		// You may not write here and this is always non blocking
+		virtual BAN::ErrorOr<size_t> write_impl(off_t, BAN::ConstByteSpan) override		{ return BAN::Error::from_errno(EINVAL); }
+		virtual BAN::ErrorOr<void> truncate_impl(size_t) override						{ return BAN::Error::from_errno(EINVAL); }
+
+		virtual bool can_read_impl() const override { return false; }
+		virtual bool can_write_impl() const override { return false; }
+		virtual bool has_error_impl() const override { return false; }
+		virtual bool has_hungup_impl() const override { return false; }
+
+	private:
+		ProcSymlinkProcessInode(Process& process, BAN::ErrorOr<BAN::String> (Process::*)() const, TmpFileSystem&, const TmpInodeInfo&);
+
+	private:
+		Process& m_process;
+		BAN::ErrorOr<BAN::String> (Process::*m_callback)() const;
+	};
+
 	class ProcROInode final : public TmpInode
 	{
 	public:

kernel/include/kernel/Process.h

@@ -225,6 +225,7 @@ namespace Kernel
 		size_t proc_meminfo(off_t offset, BAN::ByteSpan) const;
 		size_t proc_cmdline(off_t offset, BAN::ByteSpan) const;
 		size_t proc_environ(off_t offset, BAN::ByteSpan) const;
+		BAN::ErrorOr<BAN::String> proc_executable() const;
 
 		BAN::StringView executable() const { return m_executable; }
 

kernel/kernel/FS/ProcFS/Inode.cpp

@@ -17,16 +17,7 @@ namespace Kernel
 		TRY(inode->link_inode(*MUST(ProcROProcessInode::create_new(process, &Process::proc_meminfo, fs, 0400)), "meminfo"_sv));
 		TRY(inode->link_inode(*MUST(ProcROProcessInode::create_new(process, &Process::proc_cmdline, fs, 0400)), "cmdline"_sv));
 		TRY(inode->link_inode(*MUST(ProcROProcessInode::create_new(process, &Process::proc_environ, fs, 0400)), "environ"_sv));
-
+		TRY(inode->link_inode(*MUST(ProcSymlinkProcessInode::create_new(process, &Process::proc_executable, fs, 0400)), "exe"_sv));
-		TRY(inode->link_inode(*MUST(ProcSymlinkInode::create_new(
-			[](void* process) -> BAN::ErrorOr<BAN::String>
-			{
-				BAN::String result;
-				TRY(result.append(static_cast<Process*>(process)->executable()));
-				return result;
-			},
-			&process, fs, 0400, process.credentials().ruid(), process.credentials().ruid()
-		)), "exe"_sv));
 
 		return inode;
 	}
@@ -70,6 +61,29 @@ namespace Kernel
 		return (m_process.*m_callback)(offset, buffer);
 	}
 
+	BAN::ErrorOr<BAN::RefPtr<ProcSymlinkProcessInode>> ProcSymlinkProcessInode::create_new(Process& process, BAN::ErrorOr<BAN::String> (Process::*callback)() const, TmpFileSystem& fs, mode_t mode)
+	{
+		auto inode_info = create_inode_info(Mode::IFLNK | mode, 0, 0);
+
+		auto* inode_ptr = new ProcSymlinkProcessInode(process, callback, fs, inode_info);
+		if (inode_ptr == nullptr)
+			return BAN::Error::from_errno(ENOMEM);
+		return BAN::RefPtr<ProcSymlinkProcessInode>::adopt(inode_ptr);
+	}
+
+	ProcSymlinkProcessInode::ProcSymlinkProcessInode(Process& process, BAN::ErrorOr<BAN::String> (Process::*callback)() const, TmpFileSystem& fs, const TmpInodeInfo& inode_info)
+		: TmpInode(fs, MUST(fs.allocate_inode(inode_info)), inode_info)
+		, m_process(process)
+		, m_callback(callback)
+	{
+		m_inode_info.mode |= Inode::Mode::IFLNK;
+	}
+
+	BAN::ErrorOr<BAN::String> ProcSymlinkProcessInode::link_target_impl()
+	{
+		return (m_process.*m_callback)();
+	}
+
 	BAN::ErrorOr<BAN::RefPtr<ProcROInode>> ProcROInode::create_new(size_t (*callback)(off_t, BAN::ByteSpan), TmpFileSystem& fs, mode_t mode, uid_t uid, gid_t gid)
 	{
 		auto inode_info = create_inode_info(Mode::IFREG | mode, uid, gid);

kernel/kernel/Process.cpp

@@ -463,6 +463,14 @@ namespace Kernel
 		return read_from_vec_of_str(m_environ, offset, buffer);
 	}
 
+	BAN::ErrorOr<BAN::String> Process::proc_executable() const
+	{
+		LockGuard _(m_process_lock);
+		BAN::String result;
+		TRY(result.append(m_executable));
+		return result;
+	}
+
 	BAN::ErrorOr<VirtualFileSystem::File> Process::find_file(int fd, const char* path, int flags) const
 	{
 		ASSERT(m_process_lock.is_locked());