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Fix prefix-boundary hole in filer root-escape checks #5497

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Fix prefix-boundary hole in filer root-escape checks #5497

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7bc7eb9
Fix prefix-boundary hole in filer root-escape checks
simonfaltum Jun 9, 2026
a6edb6a
Remove redundant comments
simonfaltum Jun 9, 2026
6959000
Merge branch 'main' into simonfaltum/b5-filer-root-escape
simonfaltum Jun 12, 2026
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16 changes: 15 additions & 1 deletion libs/filer/local_root_path.go
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Original file line number Diff line number Diff line change
Expand Up @@ -19,7 +19,21 @@ func NewLocalRootPath(root string) localRootPath {

func (rp *localRootPath) Join(name string) (string, error) {
absPath := filepath.Join(rp.rootPath, name)
if !strings.HasPrefix(absPath, rp.rootPath) {

// An empty root carries no restriction (cmd/fs constructs unrooted local filers).
if rp.rootPath == "" {
return absPath, nil
}
Comment on lines +23 to +26

@janniklasrose janniklasrose Jun 17, 2026

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what if name = "/i-am-root-now"?


// Joining exactly the root must stay allowed: calls like ReadDir(".") resolve to it.
// Any other path must extend the root past a separator boundary; a plain prefix
// check would also accept siblings like "/root-evil" for root "/root".
// Cleaned roots like "/" or `C:\` already end in a separator.
root := rp.rootPath
if !strings.HasSuffix(root, string(filepath.Separator)) {
root += string(filepath.Separator)
}
if absPath != rp.rootPath && !strings.HasPrefix(absPath, root) {
return "", fmt.Errorf("relative path escapes root: %s", name)
}
return absPath, nil
Expand Down
43 changes: 43 additions & 0 deletions libs/filer/local_root_path_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -52,6 +52,11 @@ func testUnixLocalRootPath(t *testing.T, uncleanRoot string) {
assert.NoError(t, err)
assert.Equal(t, cleanRoot, remotePath)

// All roots in this test end in the path element "path".
remotePath, err = rp.Join("../path/x")
assert.NoError(t, err)
assert.Equal(t, cleanRoot+"/x", remotePath)

_, err = rp.Join("..")
assert.ErrorContains(t, err, `relative path escapes root: ..`)

Expand All @@ -78,6 +83,16 @@ func testUnixLocalRootPath(t *testing.T, uncleanRoot string) {

_, err = rp.Join("../..")
assert.ErrorContains(t, err, `relative path escapes root: ../..`)

// Siblings that share the root as a string prefix must be rejected.
_, err = rp.Join("../path-evil")
assert.ErrorContains(t, err, `relative path escapes root: ../path-evil`)

_, err = rp.Join("../path-evil/x")
assert.ErrorContains(t, err, `relative path escapes root: ../path-evil/x`)

_, err = rp.Join("../pathx")
assert.ErrorContains(t, err, `relative path escapes root: ../pathx`)
}

func TestUnixLocalRootPath(t *testing.T) {
Expand Down Expand Up @@ -128,6 +143,21 @@ func testWindowsLocalRootPath(t *testing.T, uncleanRoot string) {

_, err = rp.Join(`a\..\..`)
assert.ErrorContains(t, err, `relative path escapes root`)

// All roots in this test end in the path element "path".
remotePath, err = rp.Join(`..\path\x`)
assert.NoError(t, err)
assert.Equal(t, cleanRoot+`\x`, remotePath)

// Siblings that share the root as a string prefix must be rejected.
_, err = rp.Join(`..\path-evil`)
assert.ErrorContains(t, err, `relative path escapes root`)

_, err = rp.Join(`..\path-evil\x`)
assert.ErrorContains(t, err, `relative path escapes root`)

_, err = rp.Join(`..\pathx`)
assert.ErrorContains(t, err, `relative path escapes root`)
}

func TestWindowsLocalRootPath(t *testing.T) {
Expand All @@ -140,3 +170,16 @@ func TestWindowsLocalRootPath(t *testing.T) {
testWindowsLocalRootPath(t, `c:\some\root\path\.`)
testWindowsLocalRootPath(t, `C:\some\root\..\path\`)
}

func TestLocalRootPathEmptyRoot(t *testing.T) {
// An empty root is the unrooted local filer used by cmd/fs.
rp := NewLocalRootPath("")

p, err := rp.Join("a/b")
assert.NoError(t, err)
assert.Equal(t, filepath.Clean("a/b"), p)

p, err = rp.Join("../a")
assert.NoError(t, err)
assert.Equal(t, filepath.Clean("../a"), p)
}
10 changes: 9 additions & 1 deletion libs/filer/workspace_root_path.go
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Original file line number Diff line number Diff line change
Expand Up @@ -26,7 +26,15 @@ func (p *WorkspaceRootPath) Join(name string) (string, error) {
absPath := path.Join(p.rootPath, name)

// Don't allow escaping the specified root using relative paths.
if !strings.HasPrefix(absPath, p.rootPath) {
// Joining exactly the root must stay allowed: calls like ReadDir(".") resolve to it.
// Any other path must extend the root past a separator boundary; a plain prefix
// check would also accept siblings like "/root-evil" for root "/root".
// Cleaned roots like "/" (see cmd/fs) already end in a separator.
root := p.rootPath
if !strings.HasSuffix(root, "/") {
root += "/"
}
if absPath != p.rootPath && !strings.HasPrefix(absPath, root) {
return "", fmt.Errorf("relative path escapes root: %s", name)
}

Expand Down
15 changes: 15 additions & 0 deletions libs/filer/workspace_root_path_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -51,6 +51,11 @@ func testRootPath(t *testing.T, uncleanRoot string) {
assert.NoError(t, err)
assert.Equal(t, cleanRoot, remotePath)

// All roots in this test end in the path element "path".
remotePath, err = rp.Join("../path/x")
assert.NoError(t, err)
assert.Equal(t, cleanRoot+"/x", remotePath)

_, err = rp.Join("..")
assert.ErrorContains(t, err, `relative path escapes root: ..`)

Expand All @@ -77,6 +82,16 @@ func testRootPath(t *testing.T, uncleanRoot string) {

_, err = rp.Join("../..")
assert.ErrorContains(t, err, `relative path escapes root: ../..`)

// Siblings that share the root as a string prefix must be rejected.
_, err = rp.Join("../path-evil")
assert.ErrorContains(t, err, `relative path escapes root: ../path-evil`)

_, err = rp.Join("../path-evil/x")
assert.ErrorContains(t, err, `relative path escapes root: ../path-evil/x`)

_, err = rp.Join("../pathx")
assert.ErrorContains(t, err, `relative path escapes root: ../pathx`)
}

func TestRootPathClean(t *testing.T) {
Expand Down
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