io/fs, path, path/filepath, testing/fstest: validate patterns in Match, Glob

According to #28614, proposal review agreed in December 2018 that
Match should return an error for failed matches where the unmatched
part of the pattern has a syntax error. (The failed match has to date
caused the scan of the pattern to stop early.)

This change implements that behavior: the match loop continues
scanning to the end of the pattern, even after a confirmed mismatch,
to check whether the pattern is even well-formed.

The change applies to both path.Match and filepath.Match.
Then filepath.Glob and fs.Glob make a single validity-checking
call to Match before beginning their usual processing.

Also update fstest.TestFS to check for correct validation in custom
Glob implementations.

Fixes #28614.

Change-Id: Ic1d35a4bb9c3565184ae83dbefc425c5c96318e7
Reviewed-on: https://go-review.googlesource.com/c/go/+/264397
Trust: Russ Cox <rsc@golang.org>
Reviewed-by: Rob Pike <r@golang.org>

4 files changed, 89 insertions, 48 deletions

diff --git a/src/path/filepath/match.go b/src/path/filepath/match.go
index 20a334805b..c77a26952a 100644
--- a/src/path/filepath/match.go
+++ b/src/path/filepath/match.go
@@ -122,25 +122,28 @@ Scan:
 // If so, it returns the remainder of s (after the match).
 // Chunk is all single-character operators: literals, char classes, and ?.
 func matchChunk(chunk, s string) (rest string, ok bool, err error) {
+	// failed records whether the match has failed.
+	// After the match fails, the loop continues on processing chunk,
+	// checking that the pattern is well-formed but no longer reading s.
+	failed := false
 	for len(chunk) > 0 {
-		if len(s) == 0 {
-			return
+		if !failed && len(s) == 0 {
+			failed = true
 		}
 		switch chunk[0] {
 		case '[':
 			// character class
-			r, n := utf8.DecodeRuneInString(s)
-			s = s[n:]
-			chunk = chunk[1:]
-			// We can't end right after '[', we're expecting at least
-			// a closing bracket and possibly a caret.
-			if len(chunk) == 0 {
-				err = ErrBadPattern
-				return
+			var r rune
+			if !failed {
+				var n int
+				r, n = utf8.DecodeRuneInString(s)
+				s = s[n:]
 			}
+			chunk = chunk[1:]
 			// possibly negated
-			negated := chunk[0] == '^'
-			if negated {
+			negated := false
+			if len(chunk) > 0 && chunk[0] == '^' {
+				negated = true
 				chunk = chunk[1:]
 			}
 			// parse all ranges
@@ -153,12 +156,12 @@ func matchChunk(chunk, s string) (rest string, ok bool, err error) {
 				}
 				var lo, hi rune
 				if lo, chunk, err = getEsc(chunk); err != nil {
-					return
+					return "", false, err
 				}
 				hi = lo
 				if chunk[0] == '-' {
 					if hi, chunk, err = getEsc(chunk[1:]); err != nil {
-						return
+						return "", false, err
 					}
 				}
 				if lo <= r && r <= hi {
@@ -167,35 +170,41 @@ func matchChunk(chunk, s string) (rest string, ok bool, err error) {
 				nrange++
 			}
 			if match == negated {
-				return
+				failed = true
 			}
 
 		case '?':
-			if s[0] == Separator {
-				return
+			if !failed {
+				if s[0] == Separator {
+					failed = true
+				}
+				_, n := utf8.DecodeRuneInString(s)
+				s = s[n:]
 			}
-			_, n := utf8.DecodeRuneInString(s)
-			s = s[n:]
 			chunk = chunk[1:]
 
 		case '\\':
 			if runtime.GOOS != "windows" {
 				chunk = chunk[1:]
 				if len(chunk) == 0 {
-					err = ErrBadPattern
-					return
+					return "", false, ErrBadPattern
 				}
 			}
 			fallthrough
 
 		default:
-			if chunk[0] != s[0] {
-				return
+			if !failed {
+				if chunk[0] != s[0] {
+					failed = true
+				}
+				s = s[1:]
 			}
-			s = s[1:]
 			chunk = chunk[1:]
 		}
 	}
+	if failed {
+		return "", false, nil
+	}
 	return s, true, nil
 }
 
@@ -232,6 +241,10 @@ func getEsc(chunk string) (r rune, nchunk string, err error) {
 // The only possible returned error is ErrBadPattern, when pattern
 // is malformed.
 func Glob(pattern string) (matches []string, err error) {
+	// Check pattern is well-formed.
+	if _, err := Match(pattern, ""); err != nil {
+		return nil, err
+	}
 	if !hasMeta(pattern) {
 		if _, err = os.Lstat(pattern); err != nil {
 			return nil, nil
diff --git a/src/path/filepath/match_test.go b/src/path/filepath/match_test.go
index b8657626bc..1c3b567fa3 100644
--- a/src/path/filepath/match_test.go
+++ b/src/path/filepath/match_test.go
@@ -75,8 +75,10 @@ var matchTests = []MatchTest{
 	{"[", "a", false, ErrBadPattern},
 	{"[^", "a", false, ErrBadPattern},
 	{"[^bc", "a", false, ErrBadPattern},
-	{"a[", "a", false, nil},
+	{"a[", "a", false, ErrBadPattern},
 	{"a[", "ab", false, ErrBadPattern},
+	{"a[", "x", false, ErrBadPattern},
+	{"a/b[", "x", false, ErrBadPattern},
 	{"*x", "xxx", true, nil},
 }
 
@@ -155,9 +157,11 @@ func TestGlob(t *testing.T) {
 }
 
 func TestGlobError(t *testing.T) {
-	_, err := Glob("[]")
-	if err == nil {
-		t.Error("expected error for bad pattern; got none")
+	bad := []string{`[]`, `nonexist/[]`}
+	for _, pattern := range bad {
+		if _, err := Glob(pattern); err != ErrBadPattern {
+			t.Errorf("Glob(%#q) returned err=%v, want ErrBadPattern", pattern, err)
+		}
 	}
 }
 
diff --git a/src/path/match.go b/src/path/match.go
index 837eb8bb8b..918624c60e 100644
--- a/src/path/match.go
+++ b/src/path/match.go
@@ -75,6 +75,14 @@ Pattern:
 				}
 			}
 		}
+		// Before returning false with no error,
+		// check that the remainder of the pattern is syntactically valid.
+		for len(pattern) > 0 {
+			_, chunk, pattern = scanChunk(pattern)
+			if _, _, err := matchChunk(chunk, ""); err != nil {
+				return false, err
+			}
+		}
 		return false, nil
 	}
 	return len(name) == 0, nil
@@ -114,20 +122,28 @@ Scan:
 // If so, it returns the remainder of s (after the match).
 // Chunk is all single-character operators: literals, char classes, and ?.
 func matchChunk(chunk, s string) (rest string, ok bool, err error) {
+	// failed records whether the match has failed.
+	// After the match fails, the loop continues on processing chunk,
+	// checking that the pattern is well-formed but no longer reading s.
+	failed := false
 	for len(chunk) > 0 {
-		if len(s) == 0 {
-			return
+		if !failed && len(s) == 0 {
+			failed = true
 		}
 		switch chunk[0] {
 		case '[':
 			// character class
-			r, n := utf8.DecodeRuneInString(s)
-			s = s[n:]
+			var r rune
+			if !failed {
+				var n int
+				r, n = utf8.DecodeRuneInString(s)
+				s = s[n:]
+			}
 			chunk = chunk[1:]
 			// possibly negated
-			notNegated := true
+			negated := false
 			if len(chunk) > 0 && chunk[0] == '^' {
-				notNegated = false
+				negated = true
 				chunk = chunk[1:]
 			}
 			// parse all ranges
@@ -140,12 +156,12 @@ func matchChunk(chunk, s string) (rest string, ok bool, err error) {
 				}
 				var lo, hi rune
 				if lo, chunk, err = getEsc(chunk); err != nil {
-					return
+					return "", false, err
 				}
 				hi = lo
 				if chunk[0] == '-' {
 					if hi, chunk, err = getEsc(chunk[1:]); err != nil {
-						return
+						return "", false, err
 					}
 				}
 				if lo <= r && r <= hi {
@@ -153,34 +169,40 @@ func matchChunk(chunk, s string) (rest string, ok bool, err error) {
 				}
 				nrange++
 			}
-			if match != notNegated {
-				return
+			if match == negated {
+				failed = true
 			}
 
 		case '?':
-			if s[0] == '/' {
-				return
+			if !failed {
+				if s[0] == '/' {
+					failed = true
+				}
+				_, n := utf8.DecodeRuneInString(s)
+				s = s[n:]
 			}
-			_, n := utf8.DecodeRuneInString(s)
-			s = s[n:]
 			chunk = chunk[1:]
 
 		case '\\':
 			chunk = chunk[1:]
 			if len(chunk) == 0 {
-				err = ErrBadPattern
-				return
+				return "", false, ErrBadPattern
 			}
 			fallthrough
 
 		default:
-			if chunk[0] != s[0] {
-				return
+			if !failed {
+				if chunk[0] != s[0] {
+					failed = true
+				}
+				s = s[1:]
 			}
-			s = s[1:]
 			chunk = chunk[1:]
 		}
 	}
+	if failed {
+		return "", false, nil
+	}
 	return s, true, nil
 }
 
diff --git a/src/path/match_test.go b/src/path/match_test.go
index 3e027e1f68..996bd691eb 100644
--- a/src/path/match_test.go
+++ b/src/path/match_test.go
@@ -67,8 +67,10 @@ var matchTests = []MatchTest{
 	{"[", "a", false, ErrBadPattern},
 	{"[^", "a", false, ErrBadPattern},
 	{"[^bc", "a", false, ErrBadPattern},
-	{"a[", "a", false, nil},
+	{"a[", "a", false, ErrBadPattern},
 	{"a[", "ab", false, ErrBadPattern},
+	{"a[", "x", false, ErrBadPattern},
+	{"a/b[", "x", false, ErrBadPattern},
 	{"*x", "xxx", true, nil},
 }