CVE-2017-13215: crypto: algif_skcipher - Load TX SG list after waiting

commit 4f0414e54e4d1893c6f08260693f8ef84c929293 upstream.

We need to load the TX SG list in sendmsg(2) after waiting for
incoming data, not before.

[connoro@google.com: backport to 3.18, where the relevant logic is
located in skcipher_recvmsg() rather than skcipher_recvmsg_sync()]

Change-Id: I97b99469c82dd24e032b561cfd443e46a1cf75e9
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Tested-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Connor O'Brien <connoro@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>