installer: remove memmem

There's only one 'h' in the search string, so the efficiency is about
the same.

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

1 files changed, 8 insertions, 116 deletions

diff --git a/installer/customactions.c b/installer/customactions.c
index 96bd4bed..eb75d623 100644
--- a/installer/customactions.c
+++ b/installer/customactions.c
@@ -122,118 +122,6 @@ 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)
@@ -246,7 +134,7 @@ __declspec(dllexport) UINT __stdcall CheckKB2921916(MSIHANDLE installer)
 	TCHAR setupapi_path[MAX_PATH];
 	HANDLE setupapi_handle = INVALID_HANDLE_VALUE;
 	HANDLE setupapi_filemapping = NULL;
-	void *setupapi_bytes = NULL;
+	const char *setupapi_bytes = NULL;
 	MEMORY_BASIC_INFORMATION setupapi_meminfo;
 	static const char setupapi_marker[] = "Signature Hash";
 
@@ -270,9 +158,13 @@ __declspec(dllexport) UINT __stdcall CheckKB2921916(MSIHANDLE installer)
 		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;
+	if (setupapi_meminfo.RegionSize > strlen(setupapi_marker)) {
+		for (const char *p = setupapi_bytes + strlen(setupapi_marker) - 1; (p = memchr(p, 'h', setupapi_meminfo.RegionSize - (p - setupapi_bytes))); ++p) {
+			if (!memcmp(p - strlen(setupapi_marker) + 1, setupapi_marker, strlen(setupapi_marker))) {
+				ret = ERROR_SUCCESS;
+				goto out;
+			}
+		}
 	}
 
 	len = _countof(uiLevel);