net: tls: fix strparser anchor skb leak on offload RX setup failure

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

net: tls: fix strparser anchor skb leak on offload RX setup failure

When tls_set_device_offload_rx() fails at tls_dev_add(), the error path calls tls_sw_free_resources_rx() to clean up the SW context that was initialized by tls_set_sw_offload(). This function calls tls_sw_release_resources_rx() (which stops the strparser via tls_strp_stop()) and tls_sw_free_ctx_rx() (which kfrees the context), but never frees the anchor skb that was allocated by alloc_skb(0) in tls_strp_init().

Note that tls_sw_free_resources_rx() is exclusively used for this "failed to start offload" code path, there's no other caller.

The leak did not exist before commit 84c61fe1a75b ("tls: rx: do not use the standard strparser"), because the standard strparser doesn't try to pre-allocate an skb.

The normal close path in tls_sk_proto_close() handles cleanup by calling tls_sw_strparser_done() (which calls tls_strp_done()) after dropping the socket lock, because tls_strp_done() does cancel_work_sync() and the strparser work handler takes the socket lock.