base64: Properly ignore invalid characters

Not all invalid characters were ignored by base64 decoder
causing data corruption and reads beyond decode table
(faults under ASAN).

Added corresponding check into base64 unit test.

Fixes: #5627
(cherry picked from commit 726b96f)

test/unit/base64.c

@@ -58,9 +58,26 @@ base64_nowrap_test(const char *str)
 	base64_test(str, BASE64_NOWRAP, symbols, lengthof(symbols));
 }
 
+static void
+base64_invalid_chars_test(void)
+{
+	plan(1);
+
+	/* Upper bit must be cleared */
+	const char invalid_data[] = { '\x7b', '\x7c', '\x7d', '\x7e' };
+	char outbuf[8];
+
+	/* Invalid chars should be ignored, not decoded into garbage */
+	is(base64_decode(invalid_data, sizeof(invalid_data),
+	                 outbuf, sizeof(outbuf)),
+	   0, "ignoring invalid chars");
+
+	check_plan();
+}
+
 int main(int argc, char *argv[])
 {
-	plan(28);
+	plan(29);
 	header();
 
 	const char *option_tests[] = {
@@ -78,6 +95,8 @@ int main(int argc, char *argv[])
 		base64_nowrap_test(option_tests[i]);
 	}
 
+	base64_invalid_chars_test();
+
 	footer();
 	return check_plan();
 }

test/unit/base64.result

@@ -1,4 +1,4 @@
-1..28
+1..29
 	*** main ***
     1..3
     ok 1 - length
@@ -175,4 +175,7 @@ ok 27 - subtests
     ok 3 - decode length ok
     ok 4 - encode/decode
 ok 28 - subtests
+    1..1
+    ok 1 - ignoring invalid chars
+ok 29 - subtests
 	*** main: done ***

third_party/base64.c

@@ -222,7 +222,8 @@ base64_decode_value(int value)
 		32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43,
 		44, 45, 46, 47, 48, 49, 50, 51
 	};
-	static const int decoding_size = sizeof(decoding);
+	static const int decoding_size =
+		sizeof(decoding) / sizeof(decoding[0]);
 	int codepos = value;
 	codepos -= 43;
 	if (codepos < 0 || codepos >= decoding_size)