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fix: prevent stack overflow on circular key references during value expansion #412

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fix: prevent stack overflow on circular key references during value expansion #412

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27 changes: 26 additions & 1 deletion key.go
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Original file line number Diff line number Diff line change
Expand Up @@ -138,8 +138,25 @@ func (k *Key) NestedValues() []string {
return k.nestedValues
}

func hasVisitedKey(visited []*Key, k *Key) bool {
for _, v := range visited {
if v == k {
return true
}
}
return false
}

// transformValue takes a raw value and transforms to its final string.
func (k *Key) transformValue(val string) string {
return k.transformValueWithVisited(val, []*Key{k})
}

func (k *Key) transformValueWithVisited(val string, visited []*Key) string {
if len(visited) > depthValues {
return val
}

if k.s.f.ValueMapper != nil {
val = k.s.f.ValueMapper(val)
}
Expand Down Expand Up @@ -169,8 +186,16 @@ func (k *Key) transformValue(val string) string {
}
}

if hasVisitedKey(visited, nk) {
break
}

// Substitute by new value and take off leading '%(' and trailing ')s'.
val = strings.ReplaceAll(val, vr, nk.String())
res := nk.transformValueWithVisited(nk.value, append(visited, nk))
val = strings.ReplaceAll(val, vr, res)
if strings.Contains(res, vr) {
break
}
}
return val
}
Expand Down
38 changes: 38 additions & 0 deletions key_test.go
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Expand Up @@ -654,4 +654,42 @@ ENDPOINT = https://%(ACCOUNT_ID)s.r2.cloudflarestorage.com

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

t.Run("circular reference between keys should not stack overflow", func(t *testing.T) {
f, err := Load([]byte(`
[s]
a = %(b)s
b = %(a)s
`))
require.NoError(t, err)
require.NotNil(t, f)

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

t.Run("self-reference in default section should not stack overflow", func(t *testing.T) {
f, err := Load([]byte(`
a = %(a)s
`))
require.NoError(t, err)
require.NotNil(t, f)

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

t.Run("three-way circular reference should not stack overflow", func(t *testing.T) {
f, err := Load([]byte(`
[s]
a = %(b)s
b = %(c)s
c = %(a)s
`))
require.NoError(t, err)
require.NotNil(t, f)

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