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: 5068c7a883d16 ("crypto: pcrypt - Add pcrypt crypto parallelization wrapper")
Reported-by: [e-mail]
Signed-off-by: Daniel Jordan <[e-mail]>
Signed-off-by: Herbert Xu <[e-mail]>

crypto/pcrypt.c

···
 {
 	struct pcrypt_request *preq = pcrypt_padata_request(padata);
 	struct aead_request *req = pcrypt_request_ctx(preq);
+	int ret;
 
-	padata->info = crypto_aead_encrypt(req);
+	ret = crypto_aead_encrypt(req);
 
-	if (padata->info == -EINPROGRESS)
+	if (ret == -EINPROGRESS)
 		return;
 
+	padata->info = ret;
 	padata_do_serial(padata);
 }
 
···
 {
 	struct pcrypt_request *preq = pcrypt_padata_request(padata);
 	struct aead_request *req = pcrypt_request_ctx(preq);
+	int ret;
 
-	padata->info = crypto_aead_decrypt(req);
+	ret = crypto_aead_decrypt(req);
 
-	if (padata->info == -EINPROGRESS)
+	if (ret == -EINPROGRESS)
 		return;
 
+	padata->info = ret;
 	padata_do_serial(padata);
 }