mountinfo: fix ParentsFilter and PrefixFilter edge cases

mountinfo/mountinfo_filters.go

@@ -23,7 +23,7 @@ type FilterFunc func(*Info) (skip, stop bool)
 // "/foo" and "/foo/bar", and discards "/foobar".
 func PrefixFilter(prefix string) FilterFunc {
 	return func(m *Info) (bool, bool) {
-		skip := !strings.HasPrefix(m.Mountpoint+"/", prefix+"/")
+		skip := prefix != "/" && !strings.HasPrefix(m.Mountpoint+"/", prefix+"/")
 		return skip, false
 	}
 }
@@ -40,12 +40,16 @@ func SingleEntryFilter(mp string) FilterFunc {
 
 // ParentsFilter returns all entries whose mount points
 // can be parents of a path specified, discarding others.
+// The path must be absolute, have all symlinks resolved,
+// and cleaned (i.e. no extra slashes or dots).
 //
 // For example, given /var/lib/docker/something, entries
-// like /var/lib/docker, /var and / are returned.
+// like /var/lib/docker, /var and / are returned, while
+// /var/lib/dock is discarded.
 func ParentsFilter(path string) FilterFunc {
 	return func(m *Info) (bool, bool) {
-		skip := !strings.HasPrefix(path, m.Mountpoint)
+		mp := m.Mountpoint
+		skip := mp != "/" && mp != path && !strings.HasPrefix(path, mp+"/")
 		return skip, false
 	}
 }

mountinfo/mountinfo_filters_test.go

@@ -12,6 +12,9 @@ func TestPrefixFilter(t *testing.T) {
 		{prefix: "/a", mountPoint: "/a/b", shouldSkip: false},
 		{prefix: "/a", mountPoint: "/aa", shouldSkip: true},
 		{prefix: "/a", mountPoint: "/aa/b", shouldSkip: true},
+		{prefix: "/", mountPoint: "/", shouldSkip: false},
+		{prefix: "/", mountPoint: "/a", shouldSkip: false},
+		{prefix: "/", mountPoint: "/a/b", shouldSkip: false},
 
 		// invalid prefix: prefix path must be cleaned and have no trailing slash
 		{prefix: "/a/", mountPoint: "/a", shouldSkip: true},
@@ -29,3 +32,32 @@ func TestPrefixFilter(t *testing.T) {
 		}
 	}
 }
+
+func TestParentsFilter(t *testing.T) {
+	tests := []struct {
+		path       string
+		mountPoint string
+		shouldSkip bool
+	}{
+		{path: "/a/b", mountPoint: "/", shouldSkip: false},
+		{path: "/a/b", mountPoint: "/a", shouldSkip: false},
+		{path: "/a/b", mountPoint: "/a/b", shouldSkip: false},
+		{path: "/a/b", mountPoint: "/a/b/c", shouldSkip: true},
+		{path: "/a/b", mountPoint: "/b", shouldSkip: true},
+		{path: "/aa", mountPoint: "/a", shouldSkip: true},
+		{path: "/a/bb", mountPoint: "/a/b", shouldSkip: true},
+		{path: "/", mountPoint: "/", shouldSkip: false},
+		{path: "/", mountPoint: "/a", shouldSkip: true},
+	}
+	for _, tc := range tests {
+		filter := ParentsFilter(tc.path)
+		skip, _ := filter(&Info{Mountpoint: tc.mountPoint})
+		if skip != tc.shouldSkip {
+			if tc.shouldSkip {
+				t.Errorf("path %q: expected %q to be skipped", tc.path, tc.mountPoint)
+			} else {
+				t.Errorf("path %q: expected %q not to be skipped", tc.path, tc.mountPoint)
+			}
+		}
+	}
+}