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fix(windows): accept AppContainer capability grants on runtime ancestors #1447

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fix(windows): accept AppContainer capability grants on runtime ancestors #1447

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614ace2
fix(windows): accept AppContainer capability grants on runtime ancestors
mlandolfi90 Jul 28, 2026
1903de9
test(contract): pin the ancestors-only shape of the capability allowance
mlandolfi90 Aug 5, 2026
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34 changes: 26 additions & 8 deletions src/daemon/ipc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -3899,6 +3899,13 @@ static bool win_sid_is_trusted_installer(const uint8_t *sid, size_t sid_length)
return true;
}

static bool win_sid_is_app_capability(const uint8_t *sid, size_t sid_length) {
/* S-1-15-3-…: SECURITY_APP_PACKAGE_AUTHORITY, capability RID class. */
return windows_sid_valid(sid, sid_length) && sid[1] >= 1U && sid[2] == 0U && sid[3] == 0U &&
sid[4] == 0U && sid[5] == 0U && sid[6] == 0U && sid[7] == 15U &&
win_sid_read_u32_le(sid + 8U) == 3U;
}

static bool win_sid_trusted(win_security_t *security, PSID sid) {
if (!security || !sid || !security->is_valid_sid(sid)) {
return false;
Expand All @@ -3911,7 +3918,8 @@ static bool win_sid_trusted(win_security_t *security, PSID sid) {
}

static bool win_bounded_sid_trusted(win_security_t *security, const uint8_t *sid,
size_t sid_capacity, bool creator_owner_inherit_only) {
size_t sid_capacity, bool creator_owner_inherit_only,
bool ancestor_capability_ok) {
if (!security || !sid || sid_capacity < 8U || sid[1] > 15U) {
return false;
}
Expand All @@ -3927,7 +3935,14 @@ static bool win_bounded_sid_trusted(win_security_t *security, const uint8_t *sid
* user, so such an ACE only ever grants to us. Default Windows
* profile/temp ACLs (and GitHub runner profiles) carry it, and
* rejecting it locked real current-user directories out. */
security->is_well_known_sid((PSID)sid, WinCreatorOwnerRightsSid));
security->is_well_known_sid((PSID)sid, WinCreatorOwnerRightsSid) ||
/* Capability ACEs (S-1-15-3-…) grant only to AppContainer
* processes the same user's sandboxing tooling provisioned;
* agent sandboxes stamp them onto profile ancestors (AppData)
* with write rights, and refusing them locked the daemon out of
* real machines. Ancestors only: the runtime directory itself
* still demands the exact user and a protected DACL below. */
(ancestor_capability_ok && win_sid_is_app_capability(sid, sid_length)));
}

static bool win_file_owner_secure(win_security_t *security, HANDLE file,
Expand Down Expand Up @@ -3962,7 +3977,8 @@ static DWORD win_private_mutation_rights(void) {
DELETE | WRITE_DAC | WRITE_OWNER | ACCESS_SYSTEM_SECURITY;
}

static bool win_file_acl_secure(win_security_t *security, HANDLE file, DWORD mutation) {
static bool win_file_acl_secure(win_security_t *security, HANDLE file, DWORD mutation,
bool ancestor_capability_ok) {
PACL dacl = NULL;
PSECURITY_DESCRIPTOR descriptor = NULL;
DWORD status = security->get_security_info(file, SE_FILE_OBJECT, DACL_SECURITY_INFORMATION,
Expand Down Expand Up @@ -4003,7 +4019,8 @@ static bool win_file_acl_secure(win_security_t *security, HANDLE file, DWORD mut
const uint8_t *sid = (const uint8_t *)&ace->SidStart;
size_t sid_capacity = (size_t)header->AceSize - sid_offset;
bool creator_owner_inherit_only = (header->AceFlags & INHERIT_ONLY_ACE) != 0U;
if (!win_bounded_sid_trusted(security, sid, sid_capacity, creator_owner_inherit_only)) {
if (!win_bounded_sid_trusted(security, sid, sid_capacity, creator_owner_inherit_only,
ancestor_capability_ok)) {
/* Name the untrusted identity class so a harness/profile ACL leak
* (an inherited Users / Authenticated Users / Everyone ACE) is
* distinguishable from a genuinely hostile grant. */
Expand Down Expand Up @@ -4036,9 +4053,10 @@ static bool win_file_acl_secure(win_security_t *security, HANDLE file, DWORD mut
}

static bool win_file_security_secure(win_security_t *security, HANDLE file,
bool require_current_user, DWORD mutation) {
bool require_current_user, DWORD mutation,
bool ancestor_capability_ok) {
return win_file_owner_secure(security, file, require_current_user) &&
win_file_acl_secure(security, file, mutation);
win_file_acl_secure(security, file, mutation, ancestor_capability_ok);
}

static bool win_runtime_directory_secure(const wchar_t *runtime_dir) {
Expand Down Expand Up @@ -4102,7 +4120,7 @@ static bool win_runtime_directory_secure(const wchar_t *runtime_dir) {
}
bool final_private =
secure_result == ERROR_SUCCESS &&
win_file_security_secure(&security, directory, true, win_private_mutation_rights());
win_file_security_secure(&security, directory, true, win_private_mutation_rights(), false);
(void)CloseHandle(directory);
win_security_destroy(&security);
return valid_handle && owner_ok && final_private;
Expand All @@ -4125,7 +4143,7 @@ static bool win_directory_component_secure(win_security_t *security, const wchar
bool valid = GetFileInformationByHandle(directory, &info) != 0 &&
(info.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY) != 0 &&
(info.dwFileAttributes & FILE_ATTRIBUTE_REPARSE_POINT) == 0 &&
win_file_security_secure(security, directory, false, mutation);
win_file_security_secure(security, directory, false, mutation, true);
(void)CloseHandle(directory);
return valid;
}
Expand Down
7 changes: 6 additions & 1 deletion tests/test_windows_bundle_contract.sh
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Original file line number Diff line number Diff line change
Expand Up @@ -394,7 +394,12 @@ require(
needle in read("src/daemon/ipc.c")
for needle in (
"win_directory_component_secure",
"win_file_security_secure(security, directory, false, mutation)",
"win_file_security_secure(security, directory, false, mutation, true)",
# The capability allowance is ancestors-only: the final runtime
# directory must keep passing false, so a capability ACE can never
# satisfy the directory the daemon actually publishes into.
"win_private_mutation_rights(), false)",
"win_sid_is_app_capability",
"win_private_mutation_rights()",
"~((DWORD)FILE_ADD_SUBDIRECTORY)",
"FILE_ADD_FILE",
Expand Down
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