installer: check for KB2921916's setupapi.dll directly

Some people might have the right setupapi.dll without actually having
installed the quickfix. Search for a distinguishing feature instead.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

1 files changed, 144 insertions, 23 deletions

diff --git a/installer/customactions.c b/installer/customactions.c
index b61fd554..2cb629c2 100644
--- a/installer/customactions.c
+++ b/installer/customactions.c
@@ -122,6 +122,118 @@ out:
 	return ret;
 }
 
+#define MAX(a, b) ((a) > (b) ? (a) : (b))
+#define BITOP(a, b, op) ((a)[(size_t)(b) / (8 * sizeof *(a))] op(size_t) 1 << ((size_t)(b) % (8 * sizeof *(a))))
+
+static char *memmem(const void *h0, size_t k, const void *n0, size_t l)
+{
+	const unsigned char *n = n0;
+	const unsigned char *h = h0;
+	const unsigned char *z = h + k;
+	size_t i, ip, jp, p, ms, p0, mem, mem0;
+	size_t byteset[32 / sizeof(size_t)] = { 0 };
+	size_t shift[256];
+
+	/* Computing length of needle and fill shift table */
+	for (i = 0; i < l; i++)
+		BITOP(byteset, n[i], |=), shift[n[i]] = i + 1;
+
+	/* Compute maximal suffix */
+	ip = -1;
+	jp = 0;
+	k = p = 1;
+	while (jp + k < l) {
+		if (n[ip + k] == n[jp + k]) {
+			if (k == p) {
+				jp += p;
+				k = 1;
+			} else
+				k++;
+		} else if (n[ip + k] > n[jp + k]) {
+			jp += k;
+			k = 1;
+			p = jp - ip;
+		} else {
+			ip = jp++;
+			k = p = 1;
+		}
+	}
+	ms = ip;
+	p0 = p;
+
+	/* And with the opposite comparison */
+	ip = -1;
+	jp = 0;
+	k = p = 1;
+	while (jp + k < l) {
+		if (n[ip + k] == n[jp + k]) {
+			if (k == p) {
+				jp += p;
+				k = 1;
+			} else
+				k++;
+		} else if (n[ip + k] < n[jp + k]) {
+			jp += k;
+			k = 1;
+			p = jp - ip;
+		} else {
+			ip = jp++;
+			k = p = 1;
+		}
+	}
+	if (ip + 1 > ms + 1)
+		ms = ip;
+	else
+		p = p0;
+
+	/* Periodic needle? */
+	if (memcmp(n, n + p, ms + 1)) {
+		mem0 = 0;
+		p = MAX(ms, l - ms - 1) + 1;
+	} else
+		mem0 = l - p;
+	mem = 0;
+
+	/* Search loop */
+	for (;;) {
+		/* If remainder of haystack is shorter than needle, done */
+		if (z - h < l)
+			return 0;
+
+		/* Check last byte first; advance by shift on mismatch */
+		if (BITOP(byteset, h[l - 1], &)) {
+			k = l - shift[h[l - 1]];
+			if (k) {
+				if (k < mem)
+					k = mem;
+				h += k;
+				mem = 0;
+				continue;
+			}
+		} else {
+			h += l;
+			mem = 0;
+			continue;
+		}
+
+		/* Compare right half */
+		for (k = MAX(ms + 1, mem); k < l && n[k] == h[k]; k++)
+			;
+		if (k < l) {
+			h += k - ms;
+			mem = 0;
+			continue;
+		}
+		/* Compare left half */
+		for (k = ms + 1; k > mem && n[k - 1] == h[k - 1]; k--)
+			;
+		if (k <= mem)
+			return (char *)h;
+		h += p;
+		mem = mem0;
+	}
+}
+
 extern NTAPI __declspec(dllimport) void RtlGetNtVersionNumbers(DWORD *MajorVersion, DWORD *MinorVersion, DWORD *BuildNumber);
 
 __declspec(dllexport) UINT __stdcall CheckKB2921916(MSIHANDLE installer)
@@ -129,39 +241,44 @@ __declspec(dllexport) UINT __stdcall CheckKB2921916(MSIHANDLE installer)
 	bool is_com_initialized = SUCCEEDED(CoInitialize(NULL));
 	UINT ret = ERROR_SUCCESS;
 	DWORD maj, min, build, len;
-	HKEY packageKey;
-	TCHAR subkeyName[0x1000], uiLevel[10];
+	TCHAR uiLevel[10];
 	MSIHANDLE record;
+	TCHAR setupapi_path[MAX_PATH];
+	HANDLE setupapi_handle = INVALID_HANDLE_VALUE;
+	HANDLE setupapi_filemapping = NULL;
+	void *setupapi_bytes = NULL;
+	MEMORY_BASIC_INFORMATION setupapi_meminfo;
+	static const char setupapi_marker[] = "Signature Hash";
 
 	RtlGetNtVersionNumbers(&maj, &min, &build);
 	if (maj != 6 || min != 1)
 		goto out;
 
-	ret = RegOpenKeyEx(HKEY_LOCAL_MACHINE, TEXT("SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\Component Based Servicing\\Packages"), 0, KEY_ENUMERATE_SUB_KEYS, &packageKey);
-	if (ret != ERROR_SUCCESS) {
-		log_errorf(installer, LOG_LEVEL_ERR, ret, TEXT("Unable to open Component Based Servicing\\Packages registry key"));
+	ret = ERROR_INSTALL_FAILURE;
+	if (!GetSystemDirectory(setupapi_path, _countof(setupapi_path)))
+		goto out;
+	if (!PathAppend(setupapi_path, TEXT("setupapi.dll")))
+		goto out;
+	setupapi_handle = CreateFile(setupapi_path, GENERIC_READ, FILE_SHARE_READ, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
+	if (setupapi_handle == INVALID_HANDLE_VALUE)
+		goto out;
+	setupapi_filemapping = CreateFileMapping(setupapi_handle, NULL, PAGE_READONLY, 0, 0, NULL);
+	if (!setupapi_filemapping)
+		goto out;
+	setupapi_bytes = MapViewOfFile(setupapi_filemapping, FILE_MAP_READ, 0, 0, 0);
+	if (!setupapi_bytes)
+		goto out;
+	if (VirtualQuery(setupapi_bytes, &setupapi_meminfo, sizeof(setupapi_meminfo)) != sizeof(setupapi_meminfo))
+		goto out;
+	if (memmem(setupapi_bytes, setupapi_meminfo.RegionSize, setupapi_marker, strlen(setupapi_marker))) {
+		ret = ERROR_SUCCESS;
 		goto out;
 	}
-	for (DWORD i = 0;; ++i) {
-		len = _countof(subkeyName);
-		ret = RegEnumKeyEx(packageKey, i, subkeyName, &len, NULL, NULL, NULL, NULL);
-		if (ret == ERROR_NO_MORE_ITEMS)
-			break;
-		if (ret == ERROR_MORE_DATA)
-			continue;
-		if (ret != ERROR_SUCCESS) {
-			log_errorf(installer, LOG_LEVEL_ERR, ret, TEXT("Unable to enumerate Component Based Servicing\\Packages registry key"));
-			goto close_key;
-		}
-		if (_tcsstr(subkeyName, TEXT("KB2921916")))
-			goto close_key;
-	}
-	ret = ERROR_INSTALL_FAILURE;
 
 	len = _countof(uiLevel);
 	if (MsiGetProperty(installer, TEXT("UILevel"), uiLevel, &len) != ERROR_SUCCESS || _tcstoul(uiLevel, NULL, 10) < INSTALLUILEVEL_BASIC) {
 		log_messagef(installer, LOG_LEVEL_MSIERR, TEXT("Use of WireGuard on Windows 7 requires KB2921916."));
-		goto close_key;
+		goto out;
 	}
 
 #ifdef _WIN64
@@ -176,9 +293,13 @@ __declspec(dllexport) UINT __stdcall CheckKB2921916(MSIHANDLE installer)
 		ShellExecute(GetForegroundWindow(), NULL, url, NULL, NULL, SW_SHOWNORMAL);
 	MsiCloseHandle(record);
 
-close_key:
-	RegCloseKey(packageKey);
 out:
+	if (setupapi_bytes)
+		UnmapViewOfFile(setupapi_bytes);
+	if (setupapi_filemapping)
+		CloseHandle(setupapi_filemapping);
+	if (setupapi_handle != INVALID_HANDLE_VALUE)
+		CloseHandle(setupapi_handle);
 	if (is_com_initialized)
 		CoUninitialize();
 	return ret;