[spinel] check the frame buffer size before reading the next frame #10015
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When the spinel rx multiple frame buffer is full, calling `GetNextSavedFrame()` may cause the code to access the area behind the multiple frame buffer. This commit checks the received frame buffer size before reading the next frame to avoid accessing illegal area.
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Here is the backtrace we got when this issue happens. |
Size Report of OpenThread
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bukepo
reviewed
Apr 10, 2024
| @@ -371,7 +371,7 @@ template <uint16_t kSize> class MultiFrameBuffer : public FrameWritePointer | |||
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| aFrame = (aFrame == nullptr) ? mBuffer : aFrame + aLength; | |||
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| if (HasSavedFrame() && (aFrame != mWriteFrameStart)) | |||
| if (HasSavedFrame() && (aFrame != mWriteFrameStart) && ((aFrame + kHeaderSize) < GetArrayEnd(mBuffer))) | |||
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Why will there be an incomplete frame while HasSavedFrame() is true? Should we avoid saving incomplete frame?
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The function GetNextSavedFrame ()only iterate frames in the multi-frame-buffer. All frames are still be saved in the multi-frame-buffer when calling GetNextSavedFrame(), so the function HasSavedFrame () does the right job here.
abtink
reviewed
Apr 10, 2024
| @@ -371,7 +371,7 @@ template <uint16_t kSize> class MultiFrameBuffer : public FrameWritePointer | |||
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| aFrame = (aFrame == nullptr) ? mBuffer : aFrame + aLength; | |||
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| if (HasSavedFrame() && (aFrame != mWriteFrameStart)) | |||
| if (HasSavedFrame() && (aFrame != mWriteFrameStart) && ((aFrame + kHeaderSize) < GetArrayEnd(mBuffer))) | |||
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@zhanglongxia can you please share how we may get into bad state where we would need the ((aFrame + kHeaderSize) < GetArrayEnd(mBuffer)).
I tried to check the code, but cannot see how this can happen.
In SaveFrame() we have a check which makes sure we have bytes left for the next frame header, otherwise we fail (not save the frame and not change mWriteFrameStart).
otError SaveFrame(void)
{
otError error = OT_ERROR_NONE;
// If the next header will overflow the buffer, we can't save the frame.
if (!CanWrite(kHeaderSize))
{
error = OT_ERROR_NO_BUFS;
}
else
{
LittleEndian::WriteUint16(GetSkipLength() + GetLength(), mWriteFrameStart + kHeaderTotalLengthOffset);
mWriteFrameStart = mWritePointer;
IgnoreError(SetSkipLength(0));
}
return error;
}So we should always have at least kHeaderSize remaining in buffer after mWriteFrameStart?
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@zhanglongxia I think this was addressed in
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When the spinel rx multiple frame buffer is full, calling
GetNextSavedFrame()may cause the code to access the area behind the multiple frame buffer.This commit checks the received frame buffer size before reading the next frame to avoid accessing illegal area.