Overview
About vulnerability
In the Linux kernel, the following vulnerability has been resolved:
mptcp: fastopen: only mark MPTFO subflows with SYN data
Passive TCP Fast Open accepts a valid-cookie SYN even when it carries no data. In that case the child socket’s receive queue is intentionally left empty.
mptcp_fastopen_subflow_synack_set_params() set is_mptfo before checking for queued SYN data. That made data-less TFO SYNs hit a WARN and, if the warning was non-fatal, left stale MPTFO state behind. The stale flag could later trigger a state-confusion bug in check_fully_established().
Only mark the subflow as MPTFO after confirming that an SKB was queued. Return quietly when the receive queue is empty.
Note that mptcp_subflow_context’s is_mptfo field is now not just about subflows where the TFO was present, but about MPTFO subflow that consumed SYN data. Only having a valid cookie but not carrying data is not really “doing TFO”.
Details
- Affected product:
- AlmaLinux 9.2 ESU , Debian 10 ELS , TuxCare 9.6 ESU
- Affected packages:
- linux @ 4.19.0 (+2 more)