crypto: api - Fix race condition in larval lookup

https://bugzilla.redhat.com/1016108

64z is missing rhel6 commit 3af031a395c0 ("[crypto] algboss: Hold ref
count on larval") which is causing cosmetic fuzz, because crypto_alg_get
was move from crypto/api.c to crypto/internal.h.

From: Herbert Xu <herbert@gondor.apana.org.au>

[ upstream commit 77dbd7a9 ]

crypto_larval_lookup should only return a larval if it created one.
Any larval created by another entity must be processed through
crypto_larval_wait before being returned.

Otherwise this will lead to a larval being killed twice, which
will most likely lead to a crash.

Cc: stable@vger.kernel.org
Reported-by: Kees Cook <keescook@chromium.org>
Tested-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Nikola Pajkovsky <npajkovs@redhat.com>
Signed-off-by: Willy Tarreau <w@1wt.eu>

crypto/api.c

@@ -40,6 +40,8 @@ static inline struct crypto_alg *crypto_alg_get(struct crypto_alg *alg)
 	return alg;
 }
 
+static struct crypto_alg *crypto_larval_wait(struct crypto_alg *alg);
+
 struct crypto_alg *crypto_mod_get(struct crypto_alg *alg)
 {
 	return try_module_get(alg->cra_module) ? crypto_alg_get(alg) : NULL;
@@ -150,8 +152,11 @@ static struct crypto_alg *crypto_larval_add(const char *name, u32 type,
 	}
 	up_write(&crypto_alg_sem);
 
-	if (alg != &larval->alg)
+	if (alg != &larval->alg) {
 		kfree(larval);
+		if (crypto_is_larval(alg))
+			alg = crypto_larval_wait(alg);
+	}
 
 	return alg;
 }