runtime: safely load DLLs
While many other call sites have been moved to using the proper
higher-level system loading, these areas were left out. This prevents
DLL directory injection attacks. This includes both the runtime load
calls (using LoadLibrary prior) and the implicitly linked ones via
cgo_import_dynamic, which we move to our LoadLibraryEx. The goal is to
only loosely load kernel32.dll and strictly load all others.
Meanwhile we make sure that we never fallback to insecure loading on
older or unpatched systems.
This is CVE-2019-9634.
Fixes #14959
Fixes #28978
Fixes #30642
Change-Id: I401a13ed8db248ab1bb5039bf2d31915cac72b93
Reviewed-on: https://go-review.googlesource.com/c/go/+/165798
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>
diff --git a/src/runtime/os_windows.go b/src/runtime/os_windows.go
index 2e1ec58..d3e84fe 100644
--- a/src/runtime/os_windows.go
+++ b/src/runtime/os_windows.go
@@ -29,6 +29,7 @@
//go:cgo_import_dynamic runtime._GetProcessAffinityMask GetProcessAffinityMask%3 "kernel32.dll"
//go:cgo_import_dynamic runtime._GetQueuedCompletionStatus GetQueuedCompletionStatus%5 "kernel32.dll"
//go:cgo_import_dynamic runtime._GetStdHandle GetStdHandle%1 "kernel32.dll"
+//go:cgo_import_dynamic runtime._GetSystemDirectoryA GetSystemDirectoryA%2 "kernel32.dll"
//go:cgo_import_dynamic runtime._GetSystemInfo GetSystemInfo%1 "kernel32.dll"
//go:cgo_import_dynamic runtime._GetThreadContext GetThreadContext%2 "kernel32.dll"
//go:cgo_import_dynamic runtime._LoadLibraryW LoadLibraryW%1 "kernel32.dll"
@@ -47,12 +48,9 @@
//go:cgo_import_dynamic runtime._VirtualAlloc VirtualAlloc%4 "kernel32.dll"
//go:cgo_import_dynamic runtime._VirtualFree VirtualFree%3 "kernel32.dll"
//go:cgo_import_dynamic runtime._VirtualQuery VirtualQuery%3 "kernel32.dll"
-//go:cgo_import_dynamic runtime._WSAGetOverlappedResult WSAGetOverlappedResult%5 "ws2_32.dll"
//go:cgo_import_dynamic runtime._WaitForSingleObject WaitForSingleObject%2 "kernel32.dll"
//go:cgo_import_dynamic runtime._WriteConsoleW WriteConsoleW%5 "kernel32.dll"
//go:cgo_import_dynamic runtime._WriteFile WriteFile%5 "kernel32.dll"
-//go:cgo_import_dynamic runtime._timeBeginPeriod timeBeginPeriod%1 "winmm.dll"
-//go:cgo_import_dynamic runtime._timeEndPeriod timeEndPeriod%1 "winmm.dll"
type stdFunction unsafe.Pointer
@@ -75,6 +73,7 @@
_GetProcessAffinityMask,
_GetQueuedCompletionStatus,
_GetStdHandle,
+ _GetSystemDirectoryA,
_GetSystemInfo,
_GetSystemTimeAsFileTime,
_GetThreadContext,
@@ -96,12 +95,9 @@
_VirtualAlloc,
_VirtualFree,
_VirtualQuery,
- _WSAGetOverlappedResult,
_WaitForSingleObject,
_WriteConsoleW,
_WriteFile,
- _timeBeginPeriod,
- _timeEndPeriod,
_ stdFunction
// Following syscalls are only available on some Windows PCs.
@@ -109,6 +105,7 @@
_AddDllDirectory,
_AddVectoredContinueHandler,
_GetQueuedCompletionStatusEx,
+ _LoadLibraryExA,
_LoadLibraryExW,
_ stdFunction
@@ -126,6 +123,12 @@
// links wrong printf function to cgo executable (see issue
// 12030 for details).
_NtWaitForSingleObject stdFunction
+
+ // These are from non-kernel32.dll, so we prefer to LoadLibraryEx them.
+ _timeBeginPeriod,
+ _timeEndPeriod,
+ _WSAGetOverlappedResult,
+ _ stdFunction
)
// Function to be called by windows CreateThread
@@ -173,6 +176,26 @@
return stdFunction(unsafe.Pointer(f))
}
+var sysDirectory [521]byte
+var sysDirectoryLen uintptr
+
+func windowsLoadSystemLib(name []byte) uintptr {
+ if useLoadLibraryEx {
+ return stdcall3(_LoadLibraryExA, uintptr(unsafe.Pointer(&name[0])), 0, _LOAD_LIBRARY_SEARCH_SYSTEM32)
+ } else {
+ if sysDirectoryLen == 0 {
+ l := stdcall2(_GetSystemDirectoryA, uintptr(unsafe.Pointer(&sysDirectory[0])), uintptr(len(sysDirectory)-1))
+ if l == 0 || l > uintptr(len(sysDirectory)-1) {
+ throw("Unable to determine system directory")
+ }
+ sysDirectory[l] = '\\'
+ sysDirectoryLen = l + 1
+ }
+ absName := append(sysDirectory[:sysDirectoryLen], name...)
+ return stdcall1(_LoadLibraryA, uintptr(unsafe.Pointer(&absName[0])))
+ }
+}
+
func loadOptionalSyscalls() {
var kernel32dll = []byte("kernel32.dll\000")
k32 := stdcall1(_LoadLibraryA, uintptr(unsafe.Pointer(&kernel32dll[0])))
@@ -182,17 +205,19 @@
_AddDllDirectory = windowsFindfunc(k32, []byte("AddDllDirectory\000"))
_AddVectoredContinueHandler = windowsFindfunc(k32, []byte("AddVectoredContinueHandler\000"))
_GetQueuedCompletionStatusEx = windowsFindfunc(k32, []byte("GetQueuedCompletionStatusEx\000"))
+ _LoadLibraryExA = windowsFindfunc(k32, []byte("LoadLibraryExA\000"))
_LoadLibraryExW = windowsFindfunc(k32, []byte("LoadLibraryExW\000"))
+ useLoadLibraryEx = (_LoadLibraryExW != nil && _LoadLibraryExA != nil && _AddDllDirectory != nil)
var advapi32dll = []byte("advapi32.dll\000")
- a32 := stdcall1(_LoadLibraryA, uintptr(unsafe.Pointer(&advapi32dll[0])))
+ a32 := windowsLoadSystemLib(advapi32dll)
if a32 == 0 {
throw("advapi32.dll not found")
}
_RtlGenRandom = windowsFindfunc(a32, []byte("SystemFunction036\000"))
var ntdll = []byte("ntdll.dll\000")
- n32 := stdcall1(_LoadLibraryA, uintptr(unsafe.Pointer(&ntdll[0])))
+ n32 := windowsLoadSystemLib(ntdll)
if n32 == 0 {
throw("ntdll.dll not found")
}
@@ -205,6 +230,27 @@
}
}
+ var winmmdll = []byte("winmm.dll\000")
+ m32 := windowsLoadSystemLib(winmmdll)
+ if m32 == 0 {
+ throw("winmm.dll not found")
+ }
+ _timeBeginPeriod = windowsFindfunc(m32, []byte("timeBeginPeriod\000"))
+ _timeEndPeriod = windowsFindfunc(m32, []byte("timeEndPeriod\000"))
+ if _timeBeginPeriod == nil || _timeEndPeriod == nil {
+ throw("timeBegin/EndPeriod not found")
+ }
+
+ var ws232dll = []byte("ws2_32.dll\000")
+ ws232 := windowsLoadSystemLib(ws232dll)
+ if ws232 == 0 {
+ throw("ws2_32.dll not found")
+ }
+ _WSAGetOverlappedResult = windowsFindfunc(ws232, []byte("WSAGetOverlappedResult\000"))
+ if _WSAGetOverlappedResult == nil {
+ throw("WSAGetOverlappedResult not found")
+ }
+
if windowsFindfunc(n32, []byte("wine_get_version\000")) != nil {
// running on Wine
initWine(k32)
@@ -311,8 +357,6 @@
loadOptionalSyscalls()
- useLoadLibraryEx = (_LoadLibraryExW != nil && _AddDllDirectory != nil)
-
disableWER()
initExceptionHandler()
diff --git a/src/runtime/syscall_windows.go b/src/runtime/syscall_windows.go
index 8cfc711..36ad751 100644
--- a/src/runtime/syscall_windows.go
+++ b/src/runtime/syscall_windows.go
@@ -104,9 +104,13 @@
const _LOAD_LIBRARY_SEARCH_SYSTEM32 = 0x00000800
+// When available, this function will use LoadLibraryEx with the filename
+// parameter and the important SEARCH_SYSTEM32 argument. But on systems that
+// do not have that option, absoluteFilepath should contain a fallback
+// to the full path inside of system32 for use with vanilla LoadLibrary.
//go:linkname syscall_loadsystemlibrary syscall.loadsystemlibrary
//go:nosplit
-func syscall_loadsystemlibrary(filename *uint16) (handle, err uintptr) {
+func syscall_loadsystemlibrary(filename *uint16, absoluteFilepath *uint16) (handle, err uintptr) {
lockOSThread()
defer unlockOSThread()
c := &getg().m.syscall
@@ -121,15 +125,9 @@
}{filename, 0, _LOAD_LIBRARY_SEARCH_SYSTEM32}
c.args = uintptr(noescape(unsafe.Pointer(&args)))
} else {
- // User doesn't have KB2533623 installed. The caller
- // wanted to only load the filename DLL from the
- // System32 directory but that facility doesn't exist,
- // so just load it the normal way. This is a potential
- // security risk, but so is not installing security
- // updates.
c.fn = getLoadLibrary()
c.n = 1
- c.args = uintptr(noescape(unsafe.Pointer(&filename)))
+ c.args = uintptr(noescape(unsafe.Pointer(&absoluteFilepath)))
}
cgocall(asmstdcallAddr, unsafe.Pointer(c))
diff --git a/src/syscall/dll_windows.go b/src/syscall/dll_windows.go
index c57cd34..34925f7 100644
--- a/src/syscall/dll_windows.go
+++ b/src/syscall/dll_windows.go
@@ -28,7 +28,7 @@
func Syscall15(trap, nargs, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15 uintptr) (r1, r2 uintptr, err Errno)
func Syscall18(trap, nargs, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15, a16, a17, a18 uintptr) (r1, r2 uintptr, err Errno)
func loadlibrary(filename *uint16) (handle uintptr, err Errno)
-func loadsystemlibrary(filename *uint16) (handle uintptr, err Errno)
+func loadsystemlibrary(filename *uint16, absoluteFilepath *uint16) (handle uintptr, err Errno)
func getprocaddress(handle uintptr, procname *uint8) (proc uintptr, err Errno)
// A DLL implements access to a single DLL.
@@ -37,6 +37,26 @@
Handle Handle
}
+// We use this for computing the absolute path for system DLLs on systems
+// where SEARCH_SYSTEM32 is not available.
+var systemDirectoryPrefix string
+
+func init() {
+ n := uint32(MAX_PATH)
+ for {
+ b := make([]uint16, n)
+ l, e := getSystemDirectory(&b[0], n)
+ if e != nil {
+ panic("Unable to determine system directory: " + e.Error())
+ }
+ if l <= n {
+ systemDirectoryPrefix = UTF16ToString(b[:l]) + "\\"
+ break
+ }
+ n = l
+ }
+}
+
// LoadDLL loads the named DLL file into memory.
//
// If name is not an absolute path and is not a known system DLL used by
@@ -53,7 +73,11 @@
var h uintptr
var e Errno
if sysdll.IsSystemDLL[name] {
- h, e = loadsystemlibrary(namep)
+ absoluteFilepathp, err := UTF16PtrFromString(systemDirectoryPrefix + name)
+ if err != nil {
+ return nil, err
+ }
+ h, e = loadsystemlibrary(namep, absoluteFilepathp)
} else {
h, e = loadlibrary(namep)
}
diff --git a/src/syscall/security_windows.go b/src/syscall/security_windows.go
index ae8b3a1..db80d98 100644
--- a/src/syscall/security_windows.go
+++ b/src/syscall/security_windows.go
@@ -290,6 +290,7 @@
//sys OpenProcessToken(h Handle, access uint32, token *Token) (err error) = advapi32.OpenProcessToken
//sys GetTokenInformation(t Token, infoClass uint32, info *byte, infoLen uint32, returnedLen *uint32) (err error) = advapi32.GetTokenInformation
//sys GetUserProfileDirectory(t Token, dir *uint16, dirLen *uint32) (err error) = userenv.GetUserProfileDirectoryW
+//sys getSystemDirectory(dir *uint16, dirLen uint32) (len uint32, err error) = kernel32.GetSystemDirectoryW
// An access token contains the security information for a logon session.
// The system creates an access token when a user logs on, and every
diff --git a/src/syscall/zsyscall_windows.go b/src/syscall/zsyscall_windows.go
index de2d4f3..2348f65 100644
--- a/src/syscall/zsyscall_windows.go
+++ b/src/syscall/zsyscall_windows.go
@@ -190,6 +190,7 @@
procOpenProcessToken = modadvapi32.NewProc("OpenProcessToken")
procGetTokenInformation = modadvapi32.NewProc("GetTokenInformation")
procGetUserProfileDirectoryW = moduserenv.NewProc("GetUserProfileDirectoryW")
+ procGetSystemDirectoryW = modkernel32.NewProc("GetSystemDirectoryW")
)
func GetLastError() (lasterr error) {
@@ -1916,3 +1917,16 @@
}
return
}
+
+func getSystemDirectory(dir *uint16, dirLen uint32) (len uint32, err error) {
+ r0, _, e1 := Syscall(procGetSystemDirectoryW.Addr(), 2, uintptr(unsafe.Pointer(dir)), uintptr(dirLen), 0)
+ len = uint32(r0)
+ if len == 0 {
+ if e1 != 0 {
+ err = errnoErr(e1)
+ } else {
+ err = EINVAL
+ }
+ }
+ return
+}
