serenity/Kernel/Syscalls/statvfs.cpp
Ben Wiederhake 631447da57 Kernel: Fix TOCTOU in fstatvfs
In particular, fstatvfs used to assume that a file that was earlier
opened using some path will forever be at that path. This is wrong, and
in the meantime new mounts and new filesystems could take up the
filename or directories, leading to a completely inaccurate result.
This commit improves the situation:
- All filesystem information is now always accurate.
- The mount flags *might* be erroneously zero, if the custody for the
  open file is not available. I don't know when that might happen, but
  it is definitely not the typical case.
2021-11-10 16:13:10 +01:00

69 lines
2 KiB
C++

/*
* Copyright (c) 2021, Justin Mietzner <sw1tchbl4d3@sw1tchbl4d3.com>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <Kernel/FileSystem/Custody.h>
#include <Kernel/FileSystem/VirtualFileSystem.h>
#include <Kernel/Process.h>
namespace Kernel {
ErrorOr<FlatPtr> Process::do_statvfs(FileSystem const& fs, Custody const* custody, statvfs* buf)
{
statvfs kernelbuf = {};
kernelbuf.f_bsize = static_cast<u64>(fs.block_size());
kernelbuf.f_frsize = fs.fragment_size();
kernelbuf.f_blocks = fs.total_block_count();
kernelbuf.f_bfree = fs.free_block_count();
// FIXME: Implement "available blocks" into Filesystem
kernelbuf.f_bavail = fs.free_block_count();
kernelbuf.f_files = fs.total_inode_count();
kernelbuf.f_ffree = fs.free_inode_count();
kernelbuf.f_favail = fs.free_inode_count(); // FIXME: same as f_bavail
kernelbuf.f_fsid = 0; // FIXME: Implement "Filesystem ID" into Filesystem
kernelbuf.f_namemax = 255;
if (custody)
kernelbuf.f_flag = custody->mount_flags();
TRY(copy_to_user(buf, &kernelbuf));
return 0;
}
ErrorOr<FlatPtr> Process::sys$statvfs(Userspace<const Syscall::SC_statvfs_params*> user_params)
{
VERIFY_PROCESS_BIG_LOCK_ACQUIRED(this)
REQUIRE_PROMISE(rpath);
auto params = TRY(copy_typed_from_user(user_params));
auto path = TRY(get_syscall_path_argument(params.path));
auto custody = TRY(VirtualFileSystem::the().resolve_path(path->view(), current_directory(), nullptr, 0));
auto& inode = custody->inode();
auto const& fs = inode.fs();
return do_statvfs(fs, custody, params.buf);
}
ErrorOr<FlatPtr> Process::sys$fstatvfs(int fd, statvfs* buf)
{
VERIFY_PROCESS_BIG_LOCK_ACQUIRED(this)
REQUIRE_PROMISE(stdio);
auto description = TRY(fds().open_file_description(fd));
auto inode = description->inode();
if (inode == nullptr)
return ENOENT;
// FIXME: The custody that we pass in might be outdated. However, this only affects the mount flags.
return do_statvfs(inode->fs(), description->custody(), buf);
}
}