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fix(key): prevent stack overflow on cyclic key variable references #415

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31 changes: 28 additions & 3 deletions key.go
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Original file line number Diff line number Diff line change
Expand Up @@ -140,14 +140,26 @@ func (k *Key) NestedValues() []string {

// transformValue takes a raw value and transforms to its final string.
func (k *Key) transformValue(val string) string {
res, _ := k.transformValueWithVisited(val, nil)
return res
}

func (k *Key) transformValueWithVisited(val string, visited map[*Key]struct{}) (string, bool) {
if k.s.f.ValueMapper != nil {
val = k.s.f.ValueMapper(val)
}

// Fail-fast if no indicate char found for recursive value
if !strings.Contains(val, "%") {
return val
return val, false
}

if visited == nil {
visited = make(map[*Key]struct{})
}
visited[k] = struct{}{}
defer delete(visited, k)

for i := 0; i < depthValues; i++ {
vr := varPattern.FindString(val)
if len(vr) == 0 {
Expand All @@ -167,12 +179,25 @@ func (k *Key) transformValue(val string) string {
// and returns the value as-is.
break
}
if nk == k {
// Stop when key references itself to prevent cycle.
return val, true
}
}

if _, ok := visited[nk]; ok {
return val, true
}

newVal, hasCycle := nk.transformValueWithVisited(nk.value, visited)
if hasCycle {
return val, true
}

// Substitute by new value and take off leading '%(' and trailing ')s'.
val = strings.ReplaceAll(val, vr, nk.String())
val = strings.ReplaceAll(val, vr, newVal)
}
return val
return val, false
}

// String returns string representation of value.
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70 changes: 70 additions & 0 deletions key_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -654,4 +654,74 @@ ENDPOINT = https://%(ACCOUNT_ID)s.r2.cloudflarestorage.com

assert.Equal(t, "https://abc123.r2.cloudflarestorage.com", f.Section("").Key("ENDPOINT").String())
})

t.Run("self-reference in default section", func(t *testing.T) {
f, err := Load([]byte("a = %(a)s\n"))
require.NoError(t, err)
require.NotNil(t, f)

assert.Equal(t, "%(a)s", f.Section("").Key("a").String())
})

t.Run("self-reference in section", func(t *testing.T) {
f, err := Load([]byte("[s]\na = %(a)s\n"))
require.NoError(t, err)
require.NotNil(t, f)

assert.Equal(t, "%(a)s", f.Section("s").Key("a").String())
})

t.Run("mutual reference between keys in section", func(t *testing.T) {
f, err := Load([]byte("[s]\na = %(b)s\nb = %(a)s\n"))
require.NoError(t, err)
require.NotNil(t, f)

assert.Equal(t, "%(b)s", f.Section("s").Key("a").String())
assert.Equal(t, "%(a)s", f.Section("s").Key("b").String())
})

t.Run("mutual reference between keys in default section", func(t *testing.T) {
f, err := Load([]byte("a = %(b)s\nb = %(a)s\n"))
require.NoError(t, err)
require.NotNil(t, f)

assert.Equal(t, "%(b)s", f.Section("").Key("a").String())
assert.Equal(t, "%(a)s", f.Section("").Key("b").String())
})

t.Run("multi-key cyclic reference", func(t *testing.T) {
f, err := Load([]byte("[s]\na = %(b)s\nb = %(c)s\nc = %(a)s\n"))
require.NoError(t, err)
require.NotNil(t, f)

assert.Equal(t, "%(b)s", f.Section("s").Key("a").String())
assert.Equal(t, "%(c)s", f.Section("s").Key("b").String())
assert.Equal(t, "%(a)s", f.Section("s").Key("c").String())
})

t.Run("partial cycle with valid reference", func(t *testing.T) {
f, err := Load([]byte("[s]\nvalid = hello\na = %(valid)s %(b)s\nb = %(a)s\n"))
require.NoError(t, err)
require.NotNil(t, f)

assert.Equal(t, "hello %(b)s", f.Section("s").Key("a").String())
})

t.Run("diamond reference without cycle", func(t *testing.T) {
f, err := Load([]byte("[s]\nd = leaf\nb = %(d)s\nc = %(d)s\na = %(b)s and %(c)s\n"))
require.NoError(t, err)
require.NotNil(t, f)

assert.Equal(t, "leaf and leaf", f.Section("s").Key("a").String())
})

t.Run("shadows with cyclic references", func(t *testing.T) {
f, err := LoadSources(LoadOptions{AllowShadows: true}, []byte("[s]\na = %(b)s\na = %(a)s\nb = %(a)s\n"))
require.NoError(t, err)
require.NotNil(t, f)

vals := f.Section("s").Key("a").ValueWithShadows()
require.Len(t, vals, 2)
assert.Equal(t, "%(b)s", f.Section("s").Key("a").String())
})
}