fix conditions at end-of-string for base64_decode()

src/base64.c

@@ -33,6 +33,9 @@
 #include "vrt.h"
 #include "vas.h"
 
+#define ILLEGAL -1
+#define PAD -2
+
 struct b64_state_s {
 	unsigned	magic;
 #define B64_STATE_MAGIC	0xc0b64b64
@@ -53,19 +56,23 @@ alpha_init(struct b64_alphabet *alpha)
 	const char *p;
 
 	for (i = 0; i < 256; i++)
-		alpha->i64[i] = -1;
+		alpha->i64[i] = ILLEGAL;
 	for (p = alpha->b64, i = 0; *p; p++, i++)
 		alpha->i64[(int)*p] = (char)i;
 	if (alpha->padding)
-		alpha->i64[alpha->padding] = 0;
+		alpha->i64[alpha->padding] = PAD;
 }
 
 static inline int
-decode3(char *restrict *restrict dest, char *restrict const buf,
-	const size_t maxlen, unsigned u)
+decode(char *restrict *restrict dest, char *restrict const buf,
+       const size_t maxlen, unsigned u, const int n)
 {
-	char *d = *dest;
-	for (int i = 0; i < 3; i++) {
+	char *d;
+
+	if (n <= 1)
+		return -1;
+	d = *dest;
+	for (int i = 0; i < n - 1; i++) {
 		if (d == buf + maxlen)
 			return -1;
 		*d++ = (u >> 16) & 0xff;
@@ -184,7 +191,7 @@ base64_decode(const enum encoding dec, char *restrict const buf,
 	struct b64_alphabet *alpha = &b64_alphabet[dec];
 	const char *s;
 	char *dest = buf;
-	unsigned u = 0;
+	unsigned u = 0, term = 0;
 	int n;
 
 	AN(buf);
@@ -192,27 +199,35 @@ base64_decode(const enum encoding dec, char *restrict const buf,
 	for (s = p; s != vrt_magic_string_end; s = va_arg(ap, const char *)) {
 		if (s == NULL)
 			continue;
+		if (*s && term) {
+			errno = EINVAL;
+			return -1;
+		}
 		while (*s) {
 			for (n = 0; n < 4; n++) {
 				char b = alpha->i64[(unsigned) *s++];
-				if (b < 0) {
+				u <<= 6;
+				if (b == ILLEGAL) {
 					errno = EINVAL;
 					return -1;
 				}
-				u <<= 6;
+				if (b == PAD) {
+					term++;
+					continue;
+				}
 				u |= (unsigned) b;
 				if (!*s)
 					break;
 			}
 			if (n == 4)
-				if (decode3(&dest, buf, maxlen, u) < 0) {
+				if (decode(&dest, buf, maxlen, u, n-term) < 0) {
 					errno = ENOMEM;
 					return -1;
 				}
 		}
 	}
 	if (n != 4)
-		if (decode3(&dest, buf, maxlen, u) < 0) {
+		if (decode(&dest, buf, maxlen, u, n-term) < 0) {
 			errno = ENOMEM;
 			return -1;
 		}

src/tests/base64.vtc

@@ -44,6 +44,11 @@ varnish v1 -vcl+backend {
 		convert.decode(BASE64,
 	        "VGhlIHF1aWNrIGJyb3duIGZveCBqdW1wcyBvdmVyIHRoZSBsYXp5IGRvZw=="
 			      ));
+
+	    set resp.http.decenc
+	      = convert.encode(BASE64,
+			       convert.decode(BASE64, "L0hlbGxvIHdvcmxkLw=="));
+
 	}
 } -start
 
@@ -58,6 +63,7 @@ client c1 {
 	expect resp.http.b64urlnopadxcode == "L0hlbGxvIHdvcmxkLw"
 	expect resp.http.dec == "/Hello world/"
 	expect resp.http.dec2 == "The quick brown fox jumps over the lazy dog"
+	expect resp.http.decenc == "L0hlbGxvIHdvcmxkLw=="
 }
 
 client c1 -run