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Kernel: Refactor/rewrite VFS::resolve_path()

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This makes the implementation easier to follow, but also fixes multiple issues
with the old implementation. In particular, it now deals properly with . and ..
in paths, including around mount points.

Hopefully there aren't many new bugs this introduces :^)
This commit is contained in:
Sergey Bugaev 2020-01-14 13:30:15 +03:00 • committed by Andreas Kling
parent 499612482b
commit b913e30011
Notes: sideshowbarker 2024-07-19 10:03:53 +09:00
1 changed files with 52 additions and 63 deletions
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115
Kernel/FileSystem/VirtualFileSystem.cpp
View file

@ -674,8 +674,6 @@ Custody& VFS::root_custody()
KResultOr<NonnullRefPtr<Custody>> VFS::resolve_path(StringView path, Custody& base, RefPtr<Custody>* parent_custody, int options, int symlink_recursion_level)
{
// FIXME: resolve_path currently doesn't deal with .. and . . If path is ../. and base is /home/anon, it returns
// /home/anon/../. instead of /home .
if (symlink_recursion_level >= symlink_recursion_limit)
return KResult(-ELOOP);
@ -683,7 +681,6 @@ KResultOr<NonnullRefPtr<Custody>> VFS::resolve_path(StringView path, Custody& ba
return KResult(-EINVAL);
auto parts = path.split_view('/', true);
InodeIdentifier crumb_id;
auto& current_root = current->process().root_directory();
@ -691,99 +688,91 @@ KResultOr<NonnullRefPtr<Custody>> VFS::resolve_path(StringView path, Custody& ba
if (path[0] == '/') {
custody_chain.append(current_root);
crumb_id = current_root.inode().identifier();
} else {
for (auto* custody = &base; custody; custody = custody->parent()) {
// FIXME: Prepending here is not efficient! Fix this.
custody_chain.prepend(*custody);
}
crumb_id = base.inode().identifier();
}
if (parent_custody)
*parent_custody = custody_chain.last();
int mount_flags = custody_chain.last().mount_flags();
for (int i = 0; i < parts.size(); ++i) {
bool inode_was_root_at_head_of_loop = current_root.inode().identifier() == crumb_id;
auto crumb_inode = get_inode(crumb_id);
if (!crumb_inode)
return KResult(-EIO);
auto metadata = crumb_inode->metadata();
if (!metadata.is_directory())
auto& current_parent = custody_chain.last();
auto parent_metadata = current_parent.inode().metadata();
if (!parent_metadata.is_directory())
return KResult(-ENOTDIR);
if (!metadata.may_execute(current->process()))
// Ensure the current user is allowed to resolve paths inside this directory.
if (!parent_metadata.may_execute(current->process()))
return KResult(-EACCES);
auto& part = parts[i];
if (part.is_empty())
continue;
bool have_more_parts = i + 1 < parts.size();
auto& current_parent = custody_chain.last();
crumb_id = crumb_inode->lookup(part);
if (!crumb_id.is_valid()) {
if (i != parts.size() - 1) {
// We didn't find the filename we were looking for,
// and we didn't even reach the last path part.
// (ENOENT with non-null parent_custody) signals to caller that
if (part == "..") {
// If we encounter a "..", take a step back, but don't go beyond the root.
if (custody_chain.size() > 1)
custody_chain.take_last();
continue;
} else if (part == "." || part.is_empty()) {
continue;
}
// Okay, let's look up this part.
auto child_id = current_parent.inode().lookup(part);
if (!child_id.is_valid()) {
if (parent_custody) {
// ENOENT with a non-null parent custody signals to caller that
// we found the immediate parent of the file, but the file itself
// does not exist yet.
// Since this is not the immediate parent, clear parent_custody.
if (parent_custody)
*parent_custody = nullptr;
*parent_custody = have_more_parts ? nullptr : &current_parent;
}
return KResult(-ENOENT);
}
if (auto mount = find_mount_for_host(crumb_id)) {
crumb_id = mount->guest();
mount_flags = mount->flags();
}
if (inode_was_root_at_head_of_loop && crumb_id.is_root_inode() && crumb_id != current_root.inode().identifier() && part == "..") {
auto mount = find_mount_for_guest(crumb_id);
auto dir_inode = get_inode(mount->host());
ASSERT(dir_inode);
crumb_id = dir_inode->lookup("..");
}
crumb_inode = get_inode(crumb_id);
ASSERT(crumb_inode);
custody_chain.append(Custody::create(&custody_chain.last(), part, *crumb_inode, mount_flags));
metadata = crumb_inode->metadata();
if (metadata.is_directory()) {
if (i != parts.size() - 1) {
if (parent_custody)
*parent_custody = custody_chain.last();
}
int mount_flags_for_child = current_parent.mount_flags();
// See if there's something mounted on the child; in that case
// we would need to return the guest inode, not the host inode.
if (auto mount = find_mount_for_host(child_id)) {
child_id = mount->guest();
mount_flags_for_child = mount->flags();
}
if (metadata.is_symlink()) {
if (i == parts.size() - 1) {
auto child_inode = get_inode(child_id);
ASSERT(child_inode);
custody_chain.append(Custody::create(&current_parent, part, *child_inode, mount_flags_for_child));
if (child_inode->metadata().is_symlink()) {
if (!have_more_parts) {
if (options & O_NOFOLLOW)
return KResult(-ELOOP);
if (options & O_NOFOLLOW_NOERROR)
return custody_chain.last();
break;
}
auto symlink_contents = crumb_inode->read_entire();
if (!symlink_contents)
auto symlink_contents = child_inode->read_entire();
if (!symlink_contents) {
if (parent_custody)
*parent_custody = nullptr;
return KResult(-ENOENT);
}
auto symlink_path = StringView(symlink_contents.data(), symlink_contents.size());
auto symlink_target = resolve_path(symlink_path, current_parent, parent_custody, options, symlink_recursion_level + 1);
if (symlink_target.is_error())
if (symlink_target.is_error() || !have_more_parts)
return symlink_target;
bool have_more_parts = i + 1 < parts.size();
if (i + 1 == parts.size() - 1 && parts[i + 1].is_empty())
have_more_parts = false;
// Now, resolve the remaining path relative to the symlink target.
// We prepend a "." to it to ensure that it's not empty and that
// any initial slashes it might have get interpreted properly.
StringBuilder remaining_path;
remaining_path.append('.');
remaining_path.append(path.substring_view_starting_after_substring(part));
if (!have_more_parts)
return symlink_target;
StringView remaining_path = path.substring_view_starting_from_substring(parts[i + 1]);
return resolve_path(remaining_path, *symlink_target.value(), parent_custody, options, symlink_recursion_level + 1);
return resolve_path(remaining_path.to_string(), *symlink_target.value(), parent_custody, options, symlink_recursion_level + 1);
}
}
if (parent_custody)
*parent_custody = custody_chain.last().parent();
return custody_chain.last();
}