Commit `2933a8241a`

hryx <codroid@gmail.com>

2020-01-06 08:16:38

json: disallow overlong and out-of-range UTF-8

Fixes #2379 = Overlong (non-shortest) sequences UTF-8's unique encoding scheme allows for some Unicode codepoints to be represented in multiple ways. For any of these characters, the spec forbids all but the shortest form. These disallowed longer sequences are called "overlong". As an interesting side effect of this rule, the bytes C0 and C1 never appear in valid UTF-8. = Codepoint range UTF-8 disallows representation of codepoints beyond U+10FFFF, which is the highest character which can be encoded in UTF-16. Because a 4-byte sequence is capable of resulting in such characters, they must be explicitly rejected. This rule also has an interesting side effect, which is that bytes F5 to FF never appear. = References Detecting an overlong version of a codepoint could get gnarly, but luckily The Unicode Consortium did the hard work by creating this handy table of valid byte sequences: https://unicode.org/versions/corrigendum1.html I thought this mapped nicely to the parser's state machine, so I rearranged the relevant states to make use of it.

master

1 parent 9390e8b

Changed files (2)

lib

std

json

test.zig

json.zig

@@ -27,6 +27,20 @@ fn err(comptime s: []const u8) void {
     } else |_| {}
 }
 
+fn utf8Error(comptime s: []const u8) void {
+    std.testing.expect(!std.json.validate(s));
+
+    var mem_buffer: [1024 * 20]u8 = undefined;
+    const allocator = &std.heap.FixedBufferAllocator.init(&mem_buffer).allocator;
+    var p = std.json.Parser.init(allocator, false);
+
+    if (p.parse(s)) |_| {
+        unreachable;
+    } else |e| {
+        std.testing.expect(e == error.InvalidUtf8Byte);
+    }
+}
+
 fn any(comptime s: []const u8) void {
     _ = std.json.validate(s);
 
@@ -1936,3 +1950,55 @@ test "i_structure_UTF-8_BOM_empty_object" {
         \\ï»¿{}
     );
 }
+
+test "truncated UTF-8 sequence" {
+    utf8Error("\"\xc2\"");
+    utf8Error("\"\xdf\"");
+    utf8Error("\"\xed\xa0\"");
+    utf8Error("\"\xf0\x80\"");
+    utf8Error("\"\xf0\x80\x80\"");
+}
+
+test "invalid continuation byte" {
+    utf8Error("\"\xc2\x00\"");
+    utf8Error("\"\xc2\x7f\"");
+    utf8Error("\"\xc2\xc0\"");
+    utf8Error("\"\xc3\xc1\"");
+    utf8Error("\"\xc4\xf5\"");
+    utf8Error("\"\xc5\xff\"");
+    utf8Error("\"\xe4\x80\x00\"");
+    utf8Error("\"\xe5\x80\x10\"");
+    utf8Error("\"\xe6\x80\xc0\"");
+    utf8Error("\"\xe7\x80\xf5\"");
+    utf8Error("\"\xe8\x00\x80\"");
+    utf8Error("\"\xf2\x00\x80\x80\"");
+    utf8Error("\"\xf0\x80\x00\x80\"");
+    utf8Error("\"\xf1\x80\xc0\x80\"");
+    utf8Error("\"\xf2\x80\x80\x00\"");
+    utf8Error("\"\xf3\x80\x80\xc0\"");
+    utf8Error("\"\xf4\x80\x80\xf5\"");
+}
+
+test "disallowed overlong form" {
+    utf8Error("\"\xc0\x80\"");
+    utf8Error("\"\xc0\x90\"");
+    utf8Error("\"\xc1\x80\"");
+    utf8Error("\"\xc1\x90\"");
+    utf8Error("\"\xe0\x80\x80\"");
+    utf8Error("\"\xf0\x80\x80\x80\"");
+}
+
+test "out of UTF-16 range" {
+    utf8Error("\"\xf4\x90\x80\x80\"");
+    utf8Error("\"\xf5\x80\x80\x80\"");
+    utf8Error("\"\xf6\x80\x80\x80\"");
+    utf8Error("\"\xf7\x80\x80\x80\"");
+    utf8Error("\"\xf8\x80\x80\x80\"");
+    utf8Error("\"\xf9\x80\x80\x80\"");
+    utf8Error("\"\xfa\x80\x80\x80\"");
+    utf8Error("\"\xfb\x80\x80\x80\"");
+    utf8Error("\"\xfc\x80\x80\x80\"");
+    utf8Error("\"\xfd\x80\x80\x80\"");
+    utf8Error("\"\xfe\x80\x80\x80\"");
+    utf8Error("\"\xff\x80\x80\x80\"");
+}

@@ -87,6 +87,8 @@ pub const StreamingParser = struct {
     string_last_was_high_surrogate: bool,
     // Used inside of StringEscapeHexUnicode* states
     string_unicode_codepoint: u21,
+    // The first byte needs to be stored to validate 3- and 4-byte sequences.
+    sequence_first_byte: u8 = undefined,
     // When in .Number states, is the number a (still) valid integer?
     number_is_integer: bool,
 
@@ -132,9 +134,12 @@ pub const StreamingParser = struct {
         ValueBeginNoClosing,
 
         String,
-        StringUtf8Byte3,
-        StringUtf8Byte2,
-        StringUtf8Byte1,
+        StringUtf8Byte2Of2,
+        StringUtf8Byte2Of3,
+        StringUtf8Byte3Of3,
+        StringUtf8Byte2Of4,
+        StringUtf8Byte3Of4,
+        StringUtf8Byte4Of4,
         StringEscapeCharacter,
         StringEscapeHexUnicode4,
         StringEscapeHexUnicode3,
@@ -581,35 +586,68 @@ pub const StreamingParser = struct {
                     // non-control ascii
                     p.string_last_was_high_surrogate = false;
                 },
-                0xC0...0xDF => {
-                    p.state = .StringUtf8Byte1;
+                0xC2...0xDF => {
+                    p.state = .StringUtf8Byte2Of2;
                 },
                 0xE0...0xEF => {
-                    p.state = .StringUtf8Byte2;
+                    p.state = .StringUtf8Byte2Of3;
+                    p.sequence_first_byte = c;
                 },
-                0xF0...0xFF => {
-                    p.state = .StringUtf8Byte3;
+                0xF0...0xF4 => {
+                    p.state = .StringUtf8Byte2Of4;
+                    p.sequence_first_byte = c;
                 },
                 else => {
                     return error.InvalidUtf8Byte;
                 },
             },
 
-            .StringUtf8Byte3 => switch (c >> 6) {
-                0b10 => p.state = .StringUtf8Byte2,
+            .StringUtf8Byte2Of2 => switch (c >> 6) {
+                0b10 => p.state = .String,
                 else => return error.InvalidUtf8Byte,
             },
-
-            .StringUtf8Byte2 => switch (c >> 6) {
-                0b10 => p.state = .StringUtf8Byte1,
+            .StringUtf8Byte2Of3 => {
+                switch (p.sequence_first_byte) {
+                    0xE0 => switch (c) {
+                        0xA0...0xBF => {},
+                        else => return error.InvalidUtf8Byte,
+                    },
+                    0xE1...0xEF => switch (c) {
+                        0x80...0xBF => {},
+                        else => return error.InvalidUtf8Byte,
+                    },
+                    else => return error.InvalidUtf8Byte,
+                }
+                p.state = .StringUtf8Byte3Of3;
+            },
+            .StringUtf8Byte3Of3 => switch (c) {
+                0x80...0xBF => p.state = .String,
                 else => return error.InvalidUtf8Byte,
             },
-
-            .StringUtf8Byte1 => switch (c >> 6) {
-                0b10 => {
-                    p.state = .String;
-                    p.string_last_was_high_surrogate = false;
-                },
+            .StringUtf8Byte2Of4 => {
+                switch (p.sequence_first_byte) {
+                    0xF0 => switch (c) {
+                        0x90...0xBF => {},
+                        else => return error.InvalidUtf8Byte,
+                    },
+                    0xF1...0xF3 => switch (c) {
+                        0x80...0xBF => {},
+                        else => return error.InvalidUtf8Byte,
+                    },
+                    0xF4 => switch (c) {
+                        0x80...0x8F => {},
+                        else => return error.InvalidUtf8Byte,
+                    },
+                    else => return error.InvalidUtf8Byte,
+                }
+                p.state = .StringUtf8Byte3Of4;
+            },
+            .StringUtf8Byte3Of4 => switch (c) {
+                0x80...0xBF => p.state = .StringUtf8Byte4Of4,
+                else => return error.InvalidUtf8Byte,
+            },
+            .StringUtf8Byte4Of4 => switch (c) {
+                0x80...0xBF => p.state = .String,
                 else => return error.InvalidUtf8Byte,
             },

Commit 2933a8241a

Commit `2933a8241a`