From 1e0bec9bab80af86e9ebb15f1dec3dd163295265 Mon Sep 17 00:00:00 2001
From: Herbert Xu <herbert@gondor.apana.org.au>
Date: Sat, 7 Dec 2019 22:15:15 +0800
Subject: [PATCH] crypto: api - Fix race condition in crypto_spawn_alg

commit 73669cc556462f4e50376538d77ee312142e8a8a upstream.

The function crypto_spawn_alg is racy because it drops the lock
before shooting the dying algorithm.  The algorithm could disappear
altogether before we shoot it.

This patch fixes it by moving the shooting into the locked section.

Fixes: 6bfd48096ff8 ("[CRYPTO] api: Added spawns")
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>

diff --git a/crypto/algapi.c b/crypto/algapi.c
index a34baf66cff6..07ba983bf9c7 100644
--- a/crypto/algapi.c
+++ b/crypto/algapi.c
@@ -711,22 +711,16 @@ EXPORT_SYMBOL_GPL(crypto_drop_spawn);
 static struct crypto_alg *crypto_spawn_alg(struct crypto_spawn *spawn)
 {
 	struct crypto_alg *alg;
-	struct crypto_alg *alg2;
 
 	down_read(&crypto_alg_sem);
 	alg = spawn->alg;
-	alg2 = alg;
-	if (alg2)
-		alg2 = crypto_mod_get(alg2);
-	up_read(&crypto_alg_sem);
-
-	if (!alg2) {
-		if (alg)
-			crypto_shoot_alg(alg);
-		return ERR_PTR(-EAGAIN);
+	if (alg && !crypto_mod_get(alg)) {
+		alg->cra_flags |= CRYPTO_ALG_DYING;
+		alg = NULL;
 	}
+	up_read(&crypto_alg_sem);
 
-	return alg;
+	return alg ?: ERR_PTR(-EAGAIN);
 }
 
 struct crypto_tfm *crypto_spawn_tfm(struct crypto_spawn *spawn, u32 type,
diff --git a/crypto/api.c b/crypto/api.c
index 9f99d0e70384..eda0c56b8615 100644
--- a/crypto/api.c
+++ b/crypto/api.c
@@ -346,13 +346,12 @@ static unsigned int crypto_ctxsize(struct crypto_alg *alg, u32 type, u32 mask)
 	return len;
 }
 
-void crypto_shoot_alg(struct crypto_alg *alg)
+static void crypto_shoot_alg(struct crypto_alg *alg)
 {
 	down_write(&crypto_alg_sem);
 	alg->cra_flags |= CRYPTO_ALG_DYING;
 	up_write(&crypto_alg_sem);
 }
-EXPORT_SYMBOL_GPL(crypto_shoot_alg);
 
 struct crypto_tfm *__crypto_alloc_tfm(struct crypto_alg *alg, u32 type,
 				      u32 mask)
diff --git a/crypto/internal.h b/crypto/internal.h
index 93df7bec844a..e506a57e2243 100644
--- a/crypto/internal.h
+++ b/crypto/internal.h
@@ -68,7 +68,6 @@ void crypto_alg_tested(const char *name, int err);
 void crypto_remove_spawns(struct crypto_alg *alg, struct list_head *list,
 			  struct crypto_alg *nalg);
 void crypto_remove_final(struct list_head *list);
-void crypto_shoot_alg(struct crypto_alg *alg);
 struct crypto_tfm *__crypto_alloc_tfm(struct crypto_alg *alg, u32 type,
 				      u32 mask);
 void *crypto_create_tfm(struct crypto_alg *alg,
-- 
2.7.4