Medium [CVE-2026-74578] algif_skcipher - force synchronous processing on trees without ctx->state

In the Linux kernel, the following vulnerability has been resolved: crypto: algif_skcipher - force synchronous processing on trees without ctx->state The AIO/async path in skcipher_recvmsg() passes the socket-wide ctx->iv directly into the skcipher request.

After io_submit() the socket lock is dropped and the request is processed asynchronously, so a concurrent sendmsg(ALG_SET_IV) can overwrite ctx->iv and make the in-flight request run under an attacker-controlled IV. For CTR/stream modes this is IV/keystream reuse and lets an unprivileged user recover the plaintext of a concurrent operation.

Snapshotting ctx->iv into per-request storage for the async path is not sufficient.

For ciphers with statesize == 0 - which includes cbc and ctr - the MSG_MORE inter-chunk IV chaining is carried solely by the in-place req->iv writeback, which a snapshot redirects into per-request memory that af_alg_free_resources() releases on completion, silently producing wrong output.

Writing the IV back from the completion callback instead is not possible either: that would require lock_sock() there, but the callback can run in softirq/atomic context, so it must not sleep. Make the operation synchronous instead, which removes both the IV race and any writeback race.