tls: fix race between async notify and socket close

commit aec79619 upstream.

The submitting thread (one which called recvmsg/sendmsg)
may exit as soon as the async crypto handler calls complete()
so any code past that point risks touching already freed data.

Try to avoid the locking and extra flags altogether.
Have the main thread hold an extra reference, this way
we can depend solely on the atomic ref counter for
synchronization.

Don't futz with reiniting the completion, either, we are now
tightly controlling when completion fires.

Reported-by: valis <sec@valis.email>
Fixes: 0cada332 ("net/tls: fix race condition causing kernel panic")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Sabrina Dubroca <sd@queasysnail.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
[v5.15: fixed contextual conflicts in struct tls_sw_context_rx and func
init_ctx_rx; replaced DEBUG_NET_WARN_ON_ONCE with BUILD_BUG_ON_INVALID
since they're equivalent when DEBUG_NET is not defined]
Cc: <stable@vger.kernel.org> # 5.15
Signed-off-by: Shaoying Xu <shaoyi@amazon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>