crypto: api - Fix race condition in crypto_spawn_alg

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: 6bfd480 ("[CRYPTO] api: Added spawns") Signed-off-by: Herbert Xu <[email protected]>
kmaincent · Dec 11, 2019 · 73669cc · 73669cc
1 parent 4a2abbc
commit 73669cc
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Showing 3 changed files with 6 additions and 14 deletions.
diff --git a/crypto/algapi.c b/crypto/algapi.c
@@ -679,22 +679,16 @@ 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
@@ -331,13 +331,12 @@ 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
@@ -65,7 +65,6 @@ 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,