Tighten Windows sandbox restricted SIDs

codex-rs/windows-sandbox-rs/src/token.rs

@@ -1,18 +1,18 @@
 use crate::winutil::to_wide;
-use anyhow::anyhow;
 use anyhow::Result;
+use anyhow::anyhow;
 use std::ffi::c_void;
 use windows_sys::Win32::Foundation::CloseHandle;
-use windows_sys::Win32::Foundation::GetLastError;
-use windows_sys::Win32::Foundation::LocalFree;
 use windows_sys::Win32::Foundation::ERROR_SUCCESS;
+use windows_sys::Win32::Foundation::GetLastError;
 use windows_sys::Win32::Foundation::HANDLE;
 use windows_sys::Win32::Foundation::HLOCAL;
 use windows_sys::Win32::Foundation::LUID;
+use windows_sys::Win32::Foundation::LocalFree;
 use windows_sys::Win32::Security::AdjustTokenPrivileges;
-use windows_sys::Win32::Security::Authorization::SetEntriesInAclW;
 use windows_sys::Win32::Security::Authorization::EXPLICIT_ACCESS_W;
 use windows_sys::Win32::Security::Authorization::GRANT_ACCESS;
+use windows_sys::Win32::Security::Authorization::SetEntriesInAclW;
 use windows_sys::Win32::Security::Authorization::TRUSTEE_IS_SID;
 use windows_sys::Win32::Security::Authorization::TRUSTEE_IS_UNKNOWN;
 use windows_sys::Win32::Security::Authorization::TRUSTEE_W;
@@ -24,8 +24,6 @@ use windows_sys::Win32::Security::GetTokenInformation;
 use windows_sys::Win32::Security::LookupPrivilegeValueW;
 use windows_sys::Win32::Security::SetTokenInformation;
 
-use windows_sys::Win32::Security::TokenDefaultDacl;
-use windows_sys::Win32::Security::TokenGroups;
 use windows_sys::Win32::Security::ACL;
 use windows_sys::Win32::Security::SID_AND_ATTRIBUTES;
 use windows_sys::Win32::Security::TOKEN_ADJUST_DEFAULT;
@@ -35,6 +33,8 @@ use windows_sys::Win32::Security::TOKEN_ASSIGN_PRIMARY;
 use windows_sys::Win32::Security::TOKEN_DUPLICATE;
 use windows_sys::Win32::Security::TOKEN_PRIVILEGES;
 use windows_sys::Win32::Security::TOKEN_QUERY;
+use windows_sys::Win32::Security::TokenDefaultDacl;
+use windows_sys::Win32::Security::TokenGroups;
 use windows_sys::Win32::System::Threading::GetCurrentProcess;
 
 const DISABLE_MAX_PRIVILEGE: u32 = 0x01;
@@ -135,11 +135,7 @@ pub unsafe fn convert_string_sid_to_sid(s: &str) -> Option<*mut c_void> {
     }
     let mut psid: *mut c_void = std::ptr::null_mut();
     let ok = unsafe { ConvertStringSidToSidW(to_wide(s).as_ptr(), &mut psid) };
-    if ok != 0 {
-        Some(psid)
-    } else {
-        None
-    }
+    if ok != 0 { Some(psid) } else { None }
 }
 
 /// # Safety
@@ -327,6 +323,34 @@ pub unsafe fn create_readonly_token_with_caps_from(
     create_token_with_caps_from(base_token, psid_capabilities)
 }
 
+fn build_restricted_sid_entries(
+    psid_capabilities: &[*mut c_void],
+    psid_logon: *mut c_void,
+) -> Vec<SID_AND_ATTRIBUTES> {
+    let mut entries: Vec<SID_AND_ATTRIBUTES> =
+        vec![unsafe { std::mem::zeroed() }; psid_capabilities.len() + 1];
+    for (i, psid) in psid_capabilities.iter().enumerate() {
+        entries[i].Sid = *psid;
+        entries[i].Attributes = 0;
+    }
+    let logon_idx = psid_capabilities.len();
+    entries[logon_idx].Sid = psid_logon;
+    entries[logon_idx].Attributes = 0;
+    entries
+}
+
+fn build_default_dacl_sids(
+    psid_capabilities: &[*mut c_void],
+    psid_logon: *mut c_void,
+    psid_everyone: *mut c_void,
+) -> Vec<*mut c_void> {
+    let mut dacl_sids: Vec<*mut c_void> = Vec::with_capacity(psid_capabilities.len() + 2);
+    dacl_sids.push(psid_logon);
+    dacl_sids.push(psid_everyone);
+    dacl_sids.extend_from_slice(psid_capabilities);
+    dacl_sids
+}
+
 unsafe fn create_token_with_caps_from(
     base_token: HANDLE,
     psid_capabilities: &[*mut c_void],
@@ -339,18 +363,10 @@ unsafe fn create_token_with_caps_from(
     let mut everyone = world_sid()?;
     let psid_everyone = everyone.as_mut_ptr() as *mut c_void;
 
-    // Exact order: Capabilities..., Logon, Everyone
-    let mut entries: Vec<SID_AND_ATTRIBUTES> =
-        vec![std::mem::zeroed(); psid_capabilities.len() + 2];
-    for (i, psid) in psid_capabilities.iter().enumerate() {
-        entries[i].Sid = *psid;
-        entries[i].Attributes = 0;
-    }
-    let logon_idx = psid_capabilities.len();
-    entries[logon_idx].Sid = psid_logon;
-    entries[logon_idx].Attributes = 0;
-    entries[logon_idx + 1].Sid = psid_everyone;
-    entries[logon_idx + 1].Attributes = 0;
+    // Restrict writes to paths that explicitly grant one of our capability SIDs or
+    // the sandbox logon SID. Including Everyone here would reopen writes on broadly
+    // writable locations outside the configured workspace roots.
+    let mut entries = build_restricted_sid_entries(psid_capabilities, psid_logon);
 
     let mut new_token: HANDLE = 0;
     let flags = DISABLE_MAX_PRIVILEGE | LUA_TOKEN | WRITE_RESTRICTED;
@@ -369,12 +385,46 @@ unsafe fn create_token_with_caps_from(
         return Err(anyhow!("CreateRestrictedToken failed: {}", GetLastError()));
     }
 
-    let mut dacl_sids: Vec<*mut c_void> = Vec::with_capacity(psid_capabilities.len() + 2);
-    dacl_sids.push(psid_logon);
-    dacl_sids.push(psid_everyone);
-    dacl_sids.extend_from_slice(psid_capabilities);
+    let dacl_sids = build_default_dacl_sids(psid_capabilities, psid_logon, psid_everyone);
     set_default_dacl(new_token, &dacl_sids)?;
 
     enable_single_privilege(new_token, "SeChangeNotifyPrivilege")?;
     Ok(new_token)
 }
+
+#[cfg(test)]
+mod tests {
+    use super::build_default_dacl_sids;
+    use super::build_restricted_sid_entries;
+    use std::ffi::c_void;
+    use std::ptr::null_mut;
+
+    fn fake_ptr(value: usize) -> *mut c_void {
+        value as *mut c_void
+    }
+
+    #[test]
+    fn restricted_sids_exclude_everyone() {
+        let caps = [fake_ptr(0x10), fake_ptr(0x20)];
+        let logon = fake_ptr(0x30);
+        let everyone = fake_ptr(0x40);
+
+        let entries = build_restricted_sid_entries(&caps, logon);
+        let restricted: Vec<*mut c_void> = entries.iter().map(|entry| entry.Sid).collect();
+
+        assert_eq!(restricted, vec![caps[0], caps[1], logon]);
+        assert!(!restricted.contains(&everyone));
+    }
+
+    #[test]
+    fn default_dacl_keeps_everyone_for_ipc_compatibility() {
+        let caps = [fake_ptr(0x10), fake_ptr(0x20)];
+        let logon = fake_ptr(0x30);
+        let everyone = fake_ptr(0x40);
+
+        let dacl_sids = build_default_dacl_sids(&caps, logon, everyone);
+
+        assert_eq!(dacl_sids, vec![logon, everyone, caps[0], caps[1]]);
+        assert_ne!(dacl_sids[0], null_mut());
+    }
+}