crypto: api - Fix race condition in crypto_spawn_alg

[mirror_ubuntu-bionic-kernel.git] / crypto / algapi.c

diff --git a/crypto/algapi.c b/crypto/algapi.c
index 60d7366ed343e9ad6a76b9dd36be22fbd7543c89..0d62e563592a5f23072c8b8a81a279dffb0d21a2 100644 (file)
--- a/crypto/algapi.c
+++ b/crypto/algapi.c
@@ -167,6 +167,18 @@ void crypto_remove_spawns(struct crypto_alg *alg, struct list_head *list,
 
                        spawn->alg = NULL;
                        spawns = &inst->alg.cra_users;
+
+                       /*
+                        * We may encounter an unregistered instance here, since
+                        * an instance's spawns are set up prior to the instance
+                        * being registered.  An unregistered instance will have
+                        * NULL ->cra_users.next, since ->cra_users isn't
+                        * properly initialized until registration.  But an
+                        * unregistered instance cannot have any users, so treat
+                        * it the same as ->cra_users being empty.
+                        */
+                       if (spawns->next == NULL)
+                               break;
                }
        } while ((spawns = crypto_more_spawns(alg, &stack, &top,
                                              &secondary_spawns)));
@@ -640,11 +652,9 @@ EXPORT_SYMBOL_GPL(crypto_grab_spawn);
 
 void crypto_drop_spawn(struct crypto_spawn *spawn)
 {
-       if (!spawn->alg)
-               return;
-
        down_write(&crypto_alg_sem);
-       list_del(&spawn->list);
+       if (spawn->alg)
+               list_del(&spawn->list);
        up_write(&crypto_alg_sem);
 }
 EXPORT_SYMBOL_GPL(crypto_drop_spawn);
@@ -652,22 +662,16 @@ 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,