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17de90e29d
Writing to a connection goes through the flate library to compress. That writes the compressed bytes to the underlying connection. But that underlying connection is wrapped to raise a panic with an i/o error instead of returning a normal error. Jumping out of flate leaves the internal state of the compressor in undefined state. So far so good. But as part of cleaning up the connection, we could try to flush output again. Specifically: If we were writing user data, we had switched from tracing of protocol data to tracing of user data, and we registered a defer that restored the tracing kind and flushed (to ensure data was traced at the right level). That flush would cause a write into the compressor again, which could panic with an out of bounds slice access due to its inconsistent internal state. This fix prevents that compressor panic in two ways: 1. We wrap the flate.Writer with a moxio.FlateWriter that keeps track of whether a panic came out of an operation on it. If so, any further operation raises the same panic. This prevents access to the inconsistent internal flate state entirely. 2. Once we raise an i/o error, we mark the connection as broken and that makes flushes a no-op.
49 lines
1.0 KiB
Go
49 lines
1.0 KiB
Go
package moxio
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import (
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"github.com/mjl-/flate"
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)
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// FlateWriter wraps a flate.Writer and ensures no Write/Flush/Close calls are made
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// again on the underlying flate writer when a panic came out of the flate writer
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// (e.g. raised by the destination writer of the flate writer). After a panic
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// "through" a flate.Writer, its state is inconsistent and further calls could
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// panic with out of bounds slice accesses.
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type FlateWriter struct {
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w *flate.Writer
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panic any
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}
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func NewFlateWriter(w *flate.Writer) *FlateWriter {
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return &FlateWriter{w, nil}
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}
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func (w *FlateWriter) checkBroken() func() {
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if w.panic != nil {
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panic(w.panic)
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}
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return func() {
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x := recover()
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if x == nil {
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return
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}
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w.panic = x
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panic(x)
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}
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}
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func (w *FlateWriter) Write(data []byte) (int, error) {
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defer w.checkBroken()()
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return w.w.Write(data)
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}
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func (w *FlateWriter) Flush() error {
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defer w.checkBroken()()
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return w.w.Flush()
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}
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func (w *FlateWriter) Close() error {
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defer w.checkBroken()()
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return w.w.Close()
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}
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