Backport fix for crypto: algif_skcipher - Fix race condition in skcipher_check_key

Backport fix for crypto: algif_skcipher - Fix race condition in skcipher_check_key

Orabug: stable_rc4

commit 1822793a523e5d5730b19cc21160ff1717421bc8 upstream.

We need to lock the child socket in skcipher_check_key as otherwise
two simultaneous calls can cause the parent socket to be freed.

Cc: stable@vger.kernel.org
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
(cherry picked from commit 64c4131f16acba869e5280ee46e7dbf93fd8b960)

Signed-off-by: Dan Duval <dan.duval@oracle.com>