lib,permission: add permission.drop

Signed-off-by: RafaelGSS <rafael.nunu@hotmail.com>

Author: RafaelGSS

doc/api/permissions.md

@@ -76,7 +76,7 @@ flag. For WASI, use the [`--allow-wasi`][] flag.
 
 When enabling the Permission Model through the [`--permission`][]
 flag a new property `permission` is added to the `process` object.
-This property contains one function:
+This property contains the following functions:
 
 ##### `permission.has(scope[, reference])`
 
@@ -90,6 +90,36 @@ process.permission.has('fs.read'); // true
 process.permission.has('fs.read', '/home/rafaelgss/protected-folder'); // false
 ```
 
+##### `permission.drop(scope[, reference])`
+
+API call to drop permissions at runtime. This operation is **irreversible**.
+
+When called without a reference, the entire scope is dropped. When called
+with a reference, only the permission for that specific resource is revoked.
+
+You can only drop the exact resource that was explicitly granted. The
+reference passed to `drop()` must match the original grant. If a permission
+was granted using a wildcard (`*`), only the entire scope can be dropped
+(by calling `drop()` without a reference). If a directory was granted
+(e.g. `--allow-fs-read=/my/folder`), you cannot drop individual files
+inside it - you must drop the same directory that was originally granted.
+
+```js
+const fs = require('node:fs');
+
+// Read config at startup while we still have permission
+const config = fs.readFileSync('/etc/myapp/config.json', 'utf8');
+
+// Drop read access to /etc/myapp after initialization
+process.permission.drop('fs.read', '/etc/myapp');
+
+// This will now throw ERR_ACCESS_DENIED
+process.permission.has('fs.read', '/etc/myapp/config.json'); // false
+
+// Drop child process permission entirely
+process.permission.drop('child');
+```
+
 #### File System Permissions
 
 The Permission Model, by default, restricts access to the file system through the `node:fs` module.

doc/api/process.md

@@ -3197,6 +3197,65 @@ process.permission.has('fs.read', './README.md');
 process.permission.has('fs.read');
 ```
 
+### `process.permission.drop(scope[, reference])`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+> Stability: 1.1 - Active Development
+
+* `scope` {string}
+* `reference` {string}
+
+Drops the specified permission from the current process. This operation is
+**irreversible** — once a permission is dropped, it cannot be restored through
+any Node.js API.
+
+If no reference is provided, the entire scope is dropped. For example,
+`process.permission.drop('fs.read')` will revoke ALL file system read
+permissions.
+
+When a reference is provided, only the permission for that specific resource
+is dropped. For example, `process.permission.drop('fs.read', '/etc/myapp')`
+will revoke read access to that directory while keeping other read
+permissions intact.
+
+**Important:** You can only drop the exact resource that was explicitly
+granted. The reference passed to `drop()` must match the original grant:
+
+* If a permission was granted using a wildcard (`*`), such as
+  `--allow-fs-read=*`, individual paths cannot be dropped - only the entire
+  scope can be dropped (by calling `drop()` without a reference).
+* If a directory was granted (e.g. `--allow-fs-read=/my/folder`), you cannot
+  drop access to individual files inside it. You must drop the same directory
+  that was granted. Any remaining grants continue to apply.
+
+The available scopes are the same as [`process.permission.has()`][]:
+
+* `fs` - All File System (drops both read and write)
+* `fs.read` - File System read operations
+* `fs.write` - File System write operations
+* `child` - Child process spawning operations
+* `worker` - Worker thread spawning operation
+* `net` - Network operations
+* `inspector` - Inspector operations
+* `wasi` - WASI operations
+* `addon` - Native addon operations
+
+```js
+const fs = require('node:fs');
+
+// Read configuration during startup
+const config = fs.readFileSync('/etc/myapp/config.json', 'utf8');
+
+// Drop read access to the config directory after initialization
+process.permission.drop('fs.read', '/etc/myapp');
+
+// This will now throw ERR_ACCESS_DENIED
+fs.readFileSync('/etc/myapp/config.json');
+```
+
 ## `process.pid`
 
 <!-- YAML
@@ -4601,6 +4660,7 @@ cases:
 [`ChildProcess.disconnect()`]: child_process.md#subprocessdisconnect
 [`ChildProcess.send()`]: child_process.md#subprocesssendmessage-sendhandle-options-callback
 [`ChildProcess`]: child_process.md#class-childprocess
+[`ERR_ACCESS_DENIED`]: errors.md#err_access_denied
 [`Error`]: errors.md#class-error
 [`EventEmitter`]: events.md#class-eventemitter
 [`NODE_OPTIONS`]: cli.md#node_optionsoptions
@@ -4625,6 +4685,7 @@ cases:
 [`process.hrtime()`]: #processhrtimetime
 [`process.hrtime.bigint()`]: #processhrtimebigint
 [`process.kill()`]: #processkillpid-signal
+[`process.permission.has()`]: #processpermissionhasscope-reference
 [`process.setUncaughtExceptionCaptureCallback()`]: #processsetuncaughtexceptioncapturecallbackfn
 [`promise.catch()`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/catch
 [`queueMicrotask()`]: globals.md#queuemicrotaskcallback

lib/internal/process/permission.js

@@ -33,6 +33,18 @@ module.exports = ObjectFreeze({
 
     return permission.has(scope, reference);
   },
+  drop(scope, reference) {
+    validateString(scope, 'scope');
+    if (reference != null) {
+      if (isBuffer(reference)) {
+        validateBuffer(reference, 'reference');
+      } else {
+        validateString(reference, 'reference');
+      }
+    }
+
+    permission.drop(scope, reference);
+  },
   availableFlags() {
     return [
       '--allow-fs-read',

lib/internal/process/pre_execution.js

@@ -651,7 +651,7 @@ function initializePermission() {
     };
     // Guarantee path module isn't monkey-patched to bypass permission model
     ObjectFreeze(require('path'));
-    const { has } = require('internal/process/permission');
+    const { has, drop } = require('internal/process/permission');
     const warnFlags = [
       '--allow-addons',
       '--allow-child-process',
@@ -700,6 +700,7 @@ function initializePermission() {
       configurable: false,
       value: {
         has,
+        drop,
       },
     });
   } else {

src/permission/addon_permission.cc

@@ -14,6 +14,12 @@ void AddonPermission::Apply(Environment* env,
   deny_all_ = true;
 }
 
+void AddonPermission::Drop(Environment* env,
+                            PermissionScope scope,
+                            const std::string_view& param) {
+  deny_all_ = true;
+}
+
 bool AddonPermission::is_granted(Environment* env,
                                  PermissionScope perm,
                                  const std::string_view& param) const {

src/permission/addon_permission.h

@@ -15,6 +15,9 @@ class AddonPermission final : public PermissionBase {
   void Apply(Environment* env,
              const std::vector<std::string>& allow,
              PermissionScope scope) override;
+  void Drop(Environment* env,
+            PermissionScope scope,
+            const std::string_view& param = "") override;
   bool is_granted(Environment* env,
                   PermissionScope perm,
                   const std::string_view& param = "") const override;

src/permission/child_process_permission.cc

@@ -15,6 +15,12 @@ void ChildProcessPermission::Apply(Environment* env,
   deny_all_ = true;
 }
 
+void ChildProcessPermission::Drop(Environment* env,
+                                   PermissionScope scope,
+                                   const std::string_view& param) {
+  deny_all_ = true;
+}
+
 bool ChildProcessPermission::is_granted(Environment* env,
                                         PermissionScope perm,
                                         const std::string_view& param) const {

src/permission/child_process_permission.h

@@ -15,6 +15,9 @@ class ChildProcessPermission final : public PermissionBase {
   void Apply(Environment* env,
              const std::vector<std::string>& allow,
              PermissionScope scope) override;
+  void Drop(Environment* env,
+            PermissionScope scope,
+            const std::string_view& param = "") override;
   bool is_granted(Environment* env,
                   PermissionScope perm,
                   const std::string_view& param = "") const override;

src/permission/fs_permission.cc

@@ -154,15 +154,97 @@ void FSPermission::Apply(Environment* env,
   }
 }
 
+void FSPermission::Drop(Environment* env,
+                         PermissionScope scope,
+                         const std::string_view& param) {
+  if (param.empty()) {
+    // Drop all access for this scope
+    if (scope == PermissionScope::kFileSystemRead ||
+        scope == PermissionScope::kFileSystem) {
+      deny_all_in_ = true;
+      allow_all_in_ = false;
+      granted_in_fs_.Clear();
+      granted_paths_in_.clear();
+    }
+    if (scope == PermissionScope::kFileSystemWrite ||
+        scope == PermissionScope::kFileSystem) {
+      deny_all_out_ = true;
+      allow_all_out_ = false;
+      granted_out_fs_.Clear();
+      granted_paths_out_.clear();
+    }
+    return;
+  }
+
+  // When allowed with *, you can only drop * (no specific paths)
+  std::string resolved = PathResolve(env, {param});
+  if (scope == PermissionScope::kFileSystemRead ||
+      scope == PermissionScope::kFileSystem) {
+    if (!allow_all_in_) {
+      RevokeAccess(PermissionScope::kFileSystemRead, resolved);
+    }
+  }
+  if (scope == PermissionScope::kFileSystemWrite ||
+      scope == PermissionScope::kFileSystem) {
+    if (!allow_all_out_) {
+      RevokeAccess(PermissionScope::kFileSystemWrite, resolved);
+    }
+  }
+}
+
+void FSPermission::RevokeAccess(PermissionScope perm,
+                                 const std::string& res) {
+  const std::string path = WildcardIfDir(res);
+  if (perm == PermissionScope::kFileSystemRead) {
+    auto it = std::find(granted_paths_in_.begin(),
+                        granted_paths_in_.end(), path);
+    if (it != granted_paths_in_.end()) {
+      granted_paths_in_.erase(it);
+      RebuildTree(PermissionScope::kFileSystemRead);
+    }
+  } else if (perm == PermissionScope::kFileSystemWrite) {
+    auto it = std::find(granted_paths_out_.begin(),
+                        granted_paths_out_.end(), path);
+    if (it != granted_paths_out_.end()) {
+      granted_paths_out_.erase(it);
+      RebuildTree(PermissionScope::kFileSystemWrite);
+    }
+  }
+}
+
+void FSPermission::RebuildTree(PermissionScope scope) {
+  if (scope == PermissionScope::kFileSystemRead) {
+    granted_in_fs_.Clear();
+    if (granted_paths_in_.empty()) {
+      deny_all_in_ = true;
+    } else {
+      for (const auto& path : granted_paths_in_) {
+        granted_in_fs_.Insert(path);
+      }
+    }
+  } else if (scope == PermissionScope::kFileSystemWrite) {
+    granted_out_fs_.Clear();
+    if (granted_paths_out_.empty()) {
+      deny_all_out_ = true;
+    } else {
+      for (const auto& path : granted_paths_out_) {
+        granted_out_fs_.Insert(path);
+      }
+    }
+  }
+}
+
 void FSPermission::GrantAccess(PermissionScope perm, const std::string& res) {
   const std::string path = WildcardIfDir(res);
   if (perm == PermissionScope::kFileSystemRead &&
       !granted_in_fs_.Lookup(path)) {
     granted_in_fs_.Insert(path);
+    granted_paths_in_.push_back(path);
     deny_all_in_ = false;
   } else if (perm == PermissionScope::kFileSystemWrite &&
              !granted_out_fs_.Lookup(path)) {
     granted_out_fs_.Insert(path);
+    granted_paths_out_.push_back(path);
     deny_all_out_ = false;
   }
 }
@@ -196,6 +278,16 @@ FSPermission::RadixTree::~RadixTree() {
   FreeRecursivelyNode(root_node_);
 }
 
+void FSPermission::RadixTree::Clear() {
+  for (auto& c : root_node_->children) {
+    FreeRecursivelyNode(c.second);
+  }
+  root_node_->children.clear();
+  delete root_node_->wildcard_child;
+  root_node_->wildcard_child = nullptr;
+  root_node_->is_leaf = false;
+}
+
 bool FSPermission::RadixTree::Lookup(const std::string_view& s,
                                      bool when_empty_return) const {
   FSPermission::RadixTree::Node* current_node = root_node_;

src/permission/fs_permission.h

@@ -18,6 +18,9 @@ class FSPermission final : public PermissionBase {
   void Apply(Environment* env,
              const std::vector<std::string>& allow,
              PermissionScope scope) override;
+  void Drop(Environment* env,
+            PermissionScope scope,
+            const std::string_view& param = "") override;
   bool is_granted(Environment* env,
                   PermissionScope perm,
                   const std::string_view& param) const override;
@@ -139,6 +142,7 @@ class FSPermission final : public PermissionBase {
     RadixTree();
     ~RadixTree();
     void Insert(const std::string& s);
+    void Clear();
     bool Lookup(const std::string_view& s) const { return Lookup(s, false); }
     bool Lookup(const std::string_view& s, bool when_empty_return) const;
 
@@ -148,10 +152,15 @@ class FSPermission final : public PermissionBase {
 
  private:
   void GrantAccess(PermissionScope scope, const std::string& param);
+  void RevokeAccess(PermissionScope scope, const std::string& param);
+  void RebuildTree(PermissionScope scope);
   // fs granted on startup
   RadixTree granted_in_fs_;
   RadixTree granted_out_fs_;
 
+  std::vector<std::string> granted_paths_in_;
+  std::vector<std::string> granted_paths_out_;
+
   bool deny_all_in_ = true;
   bool deny_all_out_ = true;