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regexp: skip backtracker for long programs
This update makes maxBacktrackLen return 0 if len(prog.Inst) > maxBacktrackProg. This prevents an attempt to backtrack against a nil bitstate. Fixes #10319 Change-Id: Icdbeb2392782ccf66f9d0a70ea57af22fb93f01b Reviewed-on: https://go-review.googlesource.com/8473 Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
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@ -47,6 +47,9 @@ var notBacktrack *bitState = nil
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// maxBitStateLen returns the maximum length of a string to search with
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// the backtracker using prog.
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func maxBitStateLen(prog *syntax.Prog) int {
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if !shouldBacktrack(prog) {
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return 0
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}
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return maxBacktrackVector / len(prog.Inst)
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}
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@ -54,7 +57,7 @@ func maxBitStateLen(prog *syntax.Prog) int {
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// or notBacktrack if the size of the prog exceeds the maximum size that
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// the backtracker will be run for.
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func newBitState(prog *syntax.Prog) *bitState {
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if len(prog.Inst) > maxBacktrackProg {
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if !shouldBacktrack(prog) {
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return notBacktrack
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}
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return &bitState{
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@ -62,6 +65,12 @@ func newBitState(prog *syntax.Prog) *bitState {
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}
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}
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// shouldBacktrack reports whether the program is too
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// long for the backtracker to run.
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func shouldBacktrack(prog *syntax.Prog) bool {
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return len(prog.Inst) <= maxBacktrackProg
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}
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// reset resets the state of the backtracker.
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// end is the end position in the input. ncap and reqcap are the number
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// of the machine's capture registers and the number of user-requested
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@ -713,3 +713,15 @@ func TestLongest(t *testing.T) {
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t.Errorf("longest match was %q, want %q", g, w)
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}
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}
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// TestProgramTooLongForBacktrace tests that a regex which is too long
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// for the backtracker still executes properly.
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func TestProgramTooLongForBacktrack(t *testing.T) {
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longRegex := MustCompile(`(one|two|three|four|five|six|seven|eight|nine|ten|eleven|twelve|thirteen|fourteen|fifteen|sixteen|seventeen|eighteen|nineteen|twenty|twentyone|twentytwo|twentythree|twentyfour|twentyfive|twentysix|twentyseven|twentyeight|twentynine|thirty|thirtyone|thirtytwo|thirtythree|thirtyfour|thirtyfive|thirtysix|thirtyseven|thirtyeight|thirtynine|forty|fortyone|fortytwo|fortythree|fortyfour|fortyfive|fortysix|fortyseven|fortyeight|fortynine|fifty|fiftyone|fiftytwo|fiftythree|fiftyfour|fiftyfive|fiftysix|fiftyseven|fiftyeight|fiftynine|sixty|sixtyone|sixtytwo|sixtythree|sixtyfour|sixtyfive|sixtysix|sixtyseven|sixtyeight|sixtynine|seventy|seventyone|seventytwo|seventythree|seventyfour|seventyfive|seventysix|seventyseven|seventyeight|seventynine|eighty|eightyone|eightytwo|eightythree|eightyfour|eightyfive|eightysix|eightyseven|eightyeight|eightynine|ninety|ninetyone|ninetytwo|ninetythree|ninetyfour|ninetyfive|ninetysix|ninetyseven|ninetyeight|ninetynine|onehundred)`)
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if !longRegex.MatchString("two") {
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t.Errorf("longRegex.MatchString(\"two\") was false, want true")
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}
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if longRegex.MatchString("xxx") {
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t.Errorf("longRegex.MatchString(\"xxx\") was true, want false")
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}
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}
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