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Kernel: Allow unveiling subfolders regardless of parent's permissions

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This fixes a bug where unveiling a subdirectory of an already unveiled
path would sometimes be allowed and sometimes not (depending on what
other unveil calls have been made).

Now, it is always allowed to unveil a subdirectory of an already
unveiled directory, even if it has higher permissions.

This removes the need for the permissions_inherited_from_root flag in
UnveilMetadata, so it has been removed.
This commit is contained in:
Max Wipfli 2021-06-06 21:03:19 +02:00 • committed by Andreas Kling
parent 9d41dd2ed0
commit e8a317023d
3 changed files with 8 additions and 10 deletions
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2
Kernel/Process.h
View file

@ -629,7 +629,7 @@ private:
RefPtr<Timer> m_alarm_timer; RefPtr<Timer> m_alarm_timer;
VeilState m_veil_state { VeilState::None }; VeilState m_veil_state { VeilState::None };
UnveilNode m_unveiled_paths { "/", { .full_path = "/", .unveil_inherited_from_root = true } }; UnveilNode m_unveiled_paths { "/", { .full_path = "/" } };
OwnPtr<PerformanceEventBuffer> m_perf_event_buffer; OwnPtr<PerformanceEventBuffer> m_perf_event_buffer;

14
Kernel/Syscalls/unveil.cpp
View file

@ -1,5 +1,6 @@
/* /*
* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org> * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
* Copyright (c) 2021, Max Wipfli <mail@maxwipfli.ch>
* *
* SPDX-License-Identifier: BSD-2-Clause * SPDX-License-Identifier: BSD-2-Clause
*/ */
@ -90,14 +91,12 @@ KResultOr<int> Process::sys$unveil(Userspace<const Syscall::SC_unveil_params*> u
auto it = lexical_path.parts().begin(); auto it = lexical_path.parts().begin();
auto& matching_node = m_unveiled_paths.traverse_until_last_accessible_node(it, lexical_path.parts().end()); auto& matching_node = m_unveiled_paths.traverse_until_last_accessible_node(it, lexical_path.parts().end());
if (it.is_end()) { if (it.is_end()) {
auto old_permissions = matching_node.permissions(); // If the path has already been explicitly unveiled, do not allow elevating its permissions.
// Allow "elevating" the permissions when the permissions are inherited from root (/), if (matching_node.was_explicitly_unveiled()) {
// as that would be the first time this path is unveiled. if (new_permissions & ~matching_node.permissions())
if (old_permissions != UnveilAccess::None || !matching_node.permissions_inherited_from_root()) {
if (new_permissions & ~old_permissions)
return EPERM; return EPERM;
} }
matching_node.set_metadata({ matching_node.path(), (UnveilAccess)new_permissions, true, false }); matching_node.set_metadata({ matching_node.path(), (UnveilAccess)new_permissions, true });
return 0; return 0;
} }
@ -107,8 +106,9 @@ KResultOr<int> Process::sys$unveil(Userspace<const Syscall::SC_unveil_params*> u
{ new_unveiled_path, (UnveilAccess)new_permissions, true }, { new_unveiled_path, (UnveilAccess)new_permissions, true },
[](auto& parent, auto& it) -> Optional<UnveilMetadata> { [](auto& parent, auto& it) -> Optional<UnveilMetadata> {
auto path = LexicalPath::join(parent.path(), *it).string(); auto path = LexicalPath::join(parent.path(), *it).string();
return UnveilMetadata { path, parent.permissions(), false, parent.permissions_inherited_from_root() }; return UnveilMetadata { path, parent.permissions(), false };
}); });
VERIFY(m_veil_state != VeilState::Locked); VERIFY(m_veil_state != VeilState::Locked);
m_veil_state = VeilState::Dropped; m_veil_state = VeilState::Dropped;
return 0; return 0;

2
Kernel/UnveilNode.h
View file

@ -27,13 +27,11 @@ struct UnveilMetadata {
String full_path; String full_path;
UnveilAccess permissions { None }; UnveilAccess permissions { None };
bool explicitly_unveiled { false }; bool explicitly_unveiled { false };
bool unveil_inherited_from_root { false }; // true if permissions are inherited from the tree root (/).
}; };
struct UnveilNode final : public Trie<String, UnveilMetadata, Traits<String>, UnveilNode> { struct UnveilNode final : public Trie<String, UnveilMetadata, Traits<String>, UnveilNode> {
using Trie<String, UnveilMetadata, Traits<String>, UnveilNode>::Trie; using Trie<String, UnveilMetadata, Traits<String>, UnveilNode>::Trie;
bool permissions_inherited_from_root() const { return this->metadata_value().unveil_inherited_from_root; }
bool was_explicitly_unveiled() const { return this->metadata_value().explicitly_unveiled; } bool was_explicitly_unveiled() const { return this->metadata_value().explicitly_unveiled; }
UnveilAccess permissions() const { return this->metadata_value().permissions; } UnveilAccess permissions() const { return this->metadata_value().permissions; }
const String& path() const { return this->metadata_value().full_path; } const String& path() const { return this->metadata_value().full_path; }