CVE-2026-99165: sctp: revalidate output stream after association connect wait

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

sctp: revalidate output stream after association connect wait

When message interleaving is enabled, the first send waits for association establishment before building its data chunks. The wait drops the socket lock, and handshake processing can reduce the output stream count to the peer-advertised inbound stream count. sctpstreaminit() then frees the extension of every removed stream.

The sender resumes with the stream that it checked before the wait. If the peer removed that stream, sctpoutqtail() later dereferences its NULL extension. Fatal-oops policies then panic the host.

KASAN: null-ptr-deref in range [0x38-0x3f] RIP: sctpoutqtail+0x49e/0xaa0 Call Trace: sctpprimitiveSEND sctpsendmsgtoasoc sctpsendmsg

A range check alone is insufficient. Stream reconfiguration can grow the output count again while the lock is released without recreating extensions freed by the earlier shrink. The stream can then be in range while its extension remains NULL. The send-buffer wait has the same issue.

Factor the range and extension checks into a helper and repeat both after each send-path wait that drops the socket lock. Once the lock is reacquired, the validation remains stable through data creation and queueing.

If validation fails after the connect wait, the auto-created association is already established. Return ESRCH so the existing caller path keeps it under state-machine ownership instead of freeing it directly, which would leave protocol, counter and socket state inconsistent.