crypto: pcrypt - Delay write to padata->info

These three events can race when pcrypt is used multiple times in a
template ("pcrypt(pcrypt(...))"):

  1.  [taskA] The caller makes the crypto request via crypto_aead_encrypt()
  2.  [kworkerB] padata serializes the inner pcrypt request
  3.  [kworkerC] padata serializes the outer pcrypt request

3 might finish before the call to crypto_aead_encrypt() returns in 1,
resulting in two possible issues.

First, a use-after-free of the crypto request's memory when, for
example, taskA writes to the outer pcrypt request's padata->info in
pcrypt_aead_enc() after kworkerC completes the request.

Second, the outer pcrypt request overwrites the inner pcrypt request's
return code with -EINPROGRESS, making a successful request appear to
fail.  For instance, kworkerB writes the outer pcrypt request's
padata->info in pcrypt_aead_done() and then taskA overwrites it
in pcrypt_aead_enc().

Avoid both situations by delaying the write of padata->info until after
the inner crypto request's return code is checked.  This prevents the
use-after-free by not touching the crypto request's memory after the
next-inner crypto request is made, and stops padata->info from being
overwritten.

Fixes: 5068c7a8 ("crypto: pcrypt - Add pcrypt crypto parallelization wrapper")
Reported-by:  <syzbot+b187b77c8474f9648fae@syzkaller.appspotmail.com>
Signed-off-by: Daniel Jordan <daniel.m.jordan@oracle.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>