CVE-2026-89478sctp: drop a chunk if its transport was removed

Official description

In the Linux kernel, the following vulnerability has been resolved: sctp: drop a chunk if its transport was removed sctp_rcv() resolves the transport once per packet and leaves it in chunk->transport. The lookup reference, or the one sctp_add_backlog() takes if the socket is owned by userspace, keeps it around until the chunk has been processed. An authenticated ASCONF DEL-IP can remove it in the meantime. sctp_assoc_rm_peer() takes the transport out of the association and calls sctp_transport_free(), which tags it dead and drops the reference the association held. There is a window on both paths: the packet can sit on the socket backlog, and on the direct path the lookup completes before bh_lock_sock(). The DATA chunk in that packet puts the removed transport back into asoc->peer.last_data_from. Once the packet is done that reference goes away and the transport is freed by RCU, so the next delayed SACK carries the pointer into the SACK chunk and sctp_outq_select_transport() reads the freed transport's state. Drop the chunk in sctp_inq_push(), next to the existing rcvr->dead check. Both paths reach it with the association's socket lock held. The peer retransmits it.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/3fc072e7cb4a0ff251d13cfc2d24f62489cd9386
• https://git.kernel.org/stable/c/d7cb5ad832095dc4becfdb2a36007ffd50e49fb0
• https://git.kernel.org/stable/c/0422b092a3d43ca462932ff9f747731ca078d1d4
• https://git.kernel.org/stable/c/928fd7920ba37cc5637a211b9be979083413a2fa
• https://git.kernel.org/stable/c/c6c86a5e62a4fec36692ddd64b9144b660f71f96
• https://git.kernel.org/stable/c/1035bdef1efb9b1076d1a57b81e08c637ff08ecc
• https://git.kernel.org/stable/c/3537961df2163258bddc230db0e18dc14e925ea6
• https://git.kernel.org/stable/c/03a9d10ecf71f54b2af8020935f2033d4a132be5