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Fix disallow Unicode bi-directional control characters #11393

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Fix disallow Unicode bi-directional control characters #11393

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0735010
Fix disallow Unicode bi-directional control characters
straight-shoota Oct 31, 2021
15ebc9c
Disallow bidi control characters anywhere in source code
straight-shoota Oct 31, 2021
68d09ed
Add specs for escape sequences
straight-shoota Oct 31, 2021
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17 changes: 17 additions & 0 deletions spec/compiler/lexer/lexer_spec.cr
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Original file line number Diff line number Diff line change
Expand Up @@ -558,4 +558,21 @@ describe "Lexer" do
assert_syntax_error %("\\x1z"), "invalid hex escape"

assert_syntax_error %("hi\\)

# CVE-2021-42574
describe "trojan source" do
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['\u202A', '\u202B', '\u202C', '\u202D', '\u202E', '\u2066', '\u2067', '\u2068', '\u2069'].each do |char|
assert_syntax_error %(f#{char}), "Invalid unicode control character: #{char.dump}"
assert_syntax_error %("#{char}"), "Invalid unicode control character: #{char.dump}"
assert_syntax_error %(%w(#{char})), "Invalid unicode control character: #{char.dump}"
assert_syntax_error %(:#{char}), "Invalid unicode control character: #{char.dump}"
assert_syntax_error %(:"#{char}"), "Invalid unicode control character: #{char.dump}"
assert_syntax_error %(%i(#{char})), "Invalid unicode control character: #{char.dump}"
assert_syntax_error %(##{char}), "Invalid unicode control character: #{char.dump}"
assert_syntax_error %(macro foo\n##{char}\nend), "Invalid unicode control character: #{char.dump}"

it_lexes_string char.to_s.dump, char.to_s
it_lexes_char char.dump, char
end
end
end
2 changes: 1 addition & 1 deletion spec/support/syntax.cr
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Expand Up @@ -130,7 +130,7 @@ class Crystal::ASTNode
end

def assert_syntax_error(str, message = nil, line = nil, column = nil, metafile = __FILE__, metaline = __LINE__, metaendline = __END_LINE__)
it "says syntax error on #{str.inspect}", metafile, metaline, metaendline do
it "says syntax error on #{str.dump}", metafile, metaline, metaendline do
begin
parse str
fail "Expected SyntaxException to be raised", metafile, metaline
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7 changes: 4 additions & 3 deletions src/compiler/crystal/syntax/lexer.cr
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Expand Up @@ -1349,9 +1349,7 @@ module Crystal
start_pos = current_pos
end

while char != '\n' && char != '\0'
char = next_char_no_column_increment
end
skip_comment

if doc_buffer = @token.doc_buffer
doc_buffer << '\n'
Expand Down Expand Up @@ -3078,6 +3076,9 @@ module Crystal
if error = @reader.error
::raise InvalidByteSequenceError.new("Unexpected byte 0x#{error.to_s(16)} at position #{@reader.pos}, malformed UTF-8")
end
if current_char.in?('\u202A', '\u202B', '\u202C', '\u202D', '\u202E', '\u2066', '\u2067', '\u2068', '\u2069')
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How do we handle nonbreaking space? (U+00A0) That also seems potentially confusing.

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Yes, non-breaking space and other invisible characters can be confusing. But at the worst they're just invisible by themselves. They don't manipulate the display of of other visible characters like bidi control characters.
Of course, they should be invalid in most places as well, but I wouldn't necessarily go as far as disallow them entirely. That could be an option, but this definitely needs more discussion to happen in #11216.

raise "Invalid unicode control character: #{current_char.dump}"
end
char
end

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