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context: cap TLS reads during zip import #7017

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6 changes: 3 additions & 3 deletions cli/context/store/io_utils.go
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Original file line number Diff line number Diff line change
Expand Up @@ -16,14 +16,14 @@ func (l *limitedReader) Read(p []byte) (n int, err error) {
if l.N < 0 {
return 0, errors.New("read exceeds the defined limit")
}
if l.N == 0 {
return 0, io.EOF
}
Comment on lines -19 to -21

@thaJeztah thaJeztah Jun 9, 2026

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Curious; why was this condition removed?

@VrtxOmega VrtxOmega Jun 9, 2026

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Good question — this was intentional to fix a boundary detection gap with chunked reads.

The old early-return at l.N == 0 silently masks data beyond the limit as io.EOF when the underlying reader delivers data in chunks. This is realistic for zip decompression streams that don't deliver all bytes in a single Read() call.

The bug scenario:

// Underlying reader has 5 bytes but delivers them in 2-byte chunks: AB, CD, E
// Limit is 4 bytes
r := &chunkedReader{data: []byte("ABCDE"), chunkSize: 2}
lr := &limitedReader{R: r, N: 4}
data, err := io.ReadAll(lr)

// OLD: reads AB (N=2), reads CD (N=0), next call returns io.EOF
//      → ReadAll returns ("ABCD", nil) — SILENT TRUNCATION!
//      The 5th byte "E" is never detected.

// NEW: reads AB (N=2), reads CD (N=0), next call probes with 1-byte read,
//      gets "E" (N=-1) → returns error
//      → ReadAll returns ("ABCD", "read exceeds the defined limit") — CAUGHT!

The old code's if l.N == 0 { return 0, io.EOF } tells io.ReadAll "stream ended cleanly" when the underlying reader actually has more data beyond the limit. This is a security concern for the zip bomb fix — if a TLS entry decompresses to exactly 10MB in chunks, the old code returns EOF. If it's 10MB+1 byte delivered as (10MB chunk) + (1 byte chunk), the old code also returns EOF after reading 10MB, silently truncating without error.

The new code removes that early return and probes the underlying reader at the zero-remaining boundary: when N reaches 0, the next read is capped to 1 byte (N+1). If the underlying reader returns data, N goes to -1 and we report the violation. If it returns io.EOF, we propagate it cleanly.

The regression test validates this — the "Tes" (3 bytes, N=2) case catches both implementations via the N+1 cap, but the chunked scenario is where the old code fails.

// have to cap N + 1 otherwise we won't hit limit err
if int64(len(p)) > l.N+1 {
p = p[0 : l.N+1]
}
n, err = l.R.Read(p)
l.N -= int64(n)
if l.N < 0 {
return n, errors.New("read exceeds the defined limit")
}
return n, err
}
4 changes: 4 additions & 0 deletions cli/context/store/io_utils_test.go
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Expand Up @@ -21,4 +21,8 @@ func TestLimitReaderReadAll(t *testing.T) {
r = strings.NewReader("Test")
_, err = io.ReadAll(&limitedReader{R: r, N: 2})
assert.Error(t, err, "read exceeds the defined limit")

r = strings.NewReader("Tes")
_, err = io.ReadAll(&limitedReader{R: r, N: 2})
assert.Error(t, err, "read exceeds the defined limit")
}
2 changes: 1 addition & 1 deletion cli/context/store/store.go
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Expand Up @@ -478,7 +478,7 @@ func importZip(name string, s Writer, reader io.Reader) error {
if err != nil {
return err
}
data, err := io.ReadAll(f)
data, err := io.ReadAll(&limitedReader{R: f, N: maxAllowedFileSizeToImport})
defer f.Close()
if err != nil {
return err
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40 changes: 40 additions & 0 deletions cli/context/store/store_test.go
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Expand Up @@ -211,6 +211,46 @@ func TestImportZip(t *testing.T) {
assert.NilError(t, err)
}

func TestImportZipRejectsOversizedTLSFile(t *testing.T) {
testDir := t.TempDir()
zf := path.Join(testDir, "test.zip")

f, err := os.Create(zf)
assert.NilError(t, err)
defer f.Close()
w := zip.NewWriter(f)

meta, err := json.Marshal(Metadata{
Endpoints: map[string]any{
"ep1": endpoint{Foo: "bar"},
},
Metadata: context{Bar: "baz"},
Name: "source",
})
assert.NilError(t, err)

mf, err := w.Create(metaFile)
assert.NilError(t, err)
_, err = mf.Write(meta)
assert.NilError(t, err)

tlsFile, err := w.Create(path.Join("tls", "docker", "ca.pem"))
assert.NilError(t, err)
_, err = tlsFile.Write(bytes.Repeat([]byte{0}, int(maxAllowedFileSizeToImport)+1))
assert.NilError(t, err)

err = w.Close()
assert.NilError(t, err)

source, err := os.Open(zf)
assert.NilError(t, err)
defer source.Close()
var r io.Reader = source
s := New(testDir, testCfg)
err = Import("zipOversizedTLS", s, r)
assert.ErrorContains(t, err, "read exceeds the defined limit")
}

func TestImportZipInvalid(t *testing.T) {
testDir := t.TempDir()
zf := path.Join(testDir, "test.zip")
Expand Down
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