CVE-2026-31533: net/tls: fix use-after-free in -EBUSY error path of tls_do_encryption

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

net/tls: fix use-after-free in -EBUSY error path of tlsdoencryption

The -EBUSY handling in tlsdoencryption(), introduced by commit 859054147318 ("net: tls: handle backlogging of crypto requests"), has a use-after-free due to double cleanup of encryptpending and the scatterlist entry.

When cryptoaeadencrypt() returns -EBUSY, the request is enqueued to the cryptd backlog and the async callback tlsencryptdone() will be invoked upon completion. That callback unconditionally restores the scatterlist entry (sge->offset, sge->length) and decrements ctx->encryptpending. However, if tlsencryptasyncwait() returns an error, the synchronous error path in tlsdoencryption() performs the same cleanup again, double-decrementing encryptpending and double-restoring the scatterlist.

The double-decrement corrupts the encryptpending sentinel (initialized to 1), making tlsencryptasyncwait() permanently skip the wait for pending async callbacks. A subsequent sendmsg can then free the tlsrec via bpfexectxverdict() while a cryptd callback is still pending, resulting in a use-after-free when the callback fires on the freed record.

Fix this by skipping the synchronous cleanup when the -EBUSY async wait returns an error, since the callback has already handled encryptpending and sge restoration.