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Fix panics in h264 Spreader.Process - #378
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Process panicked on three kinds of received packet: - A STAP-A with a single trailing byte read the 2-byte NALU size without a length check. - A FU-A fragment small enough to fit in the trailing buffer emitted nothing, then indexed the last packet of an empty slice. - An RTP header at least as large as the MTU made the payload budget zero or negative, which panicked in sliceTo or looped forever in spreadFua. The first and third now return an error. The second is a valid stream, so the fragment is buffered and Process returns no packets. Also fix two bugs in the same path: buffered trailing data was overwritten instead of appended to when a fragment emitted nothing, and a FU-A end fragment with an empty payload dereferenced a nil pointer. An empty end FU is now emitted so the end bit is not lost. Add FuzzSpreaderProcess and regression tests.
Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## main #378 +/- ##
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+ Coverage 87.48% 88.14% +0.65%
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Files 28 28
Lines 3165 3171 +6
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+ Hits 2769 2795 +26
+ Misses 396 376 -20
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JoTurk
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Oct 13, 2026
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Thank you, we should move Spreader to pion/format in the next major release, since we don't use it directly in webrtc.
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@Sean-Der I realized that this had a correctness bug this is why i didn't merge it, but it avoids the panic, I'll follow up with the fix. |
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Spreader.Processpanicked on three kinds of received packets:The first and third now return an error. The second is a valid stream, so the fragment is buffered and Process returns no packets.
I also fixed two non-panicking bugs.
Buffered trailing data was overwritten instead of appended to when a fragment emitted nothing, and a FU-A end fragment with an empty payload dereferenced a nil pointer. An empty end FU is now emitted so the end bit is not lost.
Also added FuzzSpreaderProcess and regression tests.
The panics were found using an unreleased static analysis tool written by me. The fixes were implemented with the help of AI.