sctp: avoid livelock while updating retransmit path

Overview

In the Linux kernel, the following vulnerability has been resolved:

sctp: avoid livelock while updating retransmit path

sctp_assoc_update_retran_path() can loop forever when every remaining transport, including retran_path, is SCTP_UNCONFIRMED: the state check runs before the wraparound test, so the loop cannot observe that it has completed a full pass.

Fix this by considering a transport only when it is not UNCONFIRMED, then checking whether the walk has returned to retran_path. This makes the full-pass termination independent of the transport state while preserving the existing fallback selection semantics.

Also restore the NULL guard around the retran_path assignment. In the all-UNCONFIRMED case there is no eligible replacement transport, and installing NULL would leave later retransmit-path users and the debug print with a NULL path.

Affected

• Linux >= 4c47af4d5eb2c2f78f886079a3920a7078a6f0a0 < 3fe624c3843694ab096fdb198526ba0c659febbe
• Linux >= 4c47af4d5eb2c2f78f886079a3920a7078a6f0a0 < 43410c1f2db53516e95ddd7e5b4b02f495b78121
• Linux >= 4c47af4d5eb2c2f78f886079a3920a7078a6f0a0 < d893a7cc1cb41dd510f338bb2bfd8f29b14eaf49
• Linux >= 4c47af4d5eb2c2f78f886079a3920a7078a6f0a0 < 83b1a7f9e718828ef364a7b004254ebb2d0035fe
• Linux >= 4c47af4d5eb2c2f78f886079a3920a7078a6f0a0 < 173610fff55022a5ad1579fbcc7faa97467b58b7
• Linux >= 4c47af4d5eb2c2f78f886079a3920a7078a6f0a0 < c9338057df1025f578fe7d0ff08bada87b8b838d
• Linux >= 4c47af4d5eb2c2f78f886079a3920a7078a6f0a0 < ddc34cc0834c873871e88b055ee6a260676efe97
• Linux >= 4c47af4d5eb2c2f78f886079a3920a7078a6f0a0 < d2c31b837406395e576afeb25958c98e9938f3f6
• Linux 8ceaec02b17397d12719a282945abc95f8149d9f
• Linux d2c2bdcdd8c5ce3d2a68aa3353ed1f340c3e500e
• Linux >= 3.10.106 < 3.11
• Linux >= 3.12.71 < 3.13
• Linux 3.14

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.