tcp_send_buffered.c: Fix broken retransmit #4159
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With an applictation using mbedtls, I observed retransmitted segments with corrupted user data, detected by the peer tls during mac processing. Looking at the packet dump, I suspect that a wrb which has been put back onto the write_q for retransmission was partially sent but fully acked. Note: it's normal for a retransmission to be acked before sent. In that case, the bug fixed in this commit would cause the wrb have a wrong sequence number, possibly the same as the next wrb. It matches what I saw in the packet dump. That is, the broken segments contain the payload identical to one of the previous segment.
xiaoxiang781216
approved these changes
Aug 2, 2021
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Summary
With an applictation using mbedtls, I observed retransmitted segments
with corrupted user data, detected by the peer tls during mac processing.
Looking at the packet dump, I suspect that a wrb which has been put back
onto the write_q for retransmission was partially sent but fully acked.
Note: it's normal for a retransmission to be acked before sent.
In that case, the bug fixed in this commit would cause the wrb have
a wrong sequence number, possibly the same as the next wrb. It matches
what I saw in the packet dump. That is, the broken segments contain the
payload identical to one of the previous segment.
Impact
tcp
Testing
tested with some of other patches in #4184
on esp32 and sim