From be924e0aaa315a179c25221685e3f1a35a70156e Mon Sep 17 00:00:00 2001 From: Eric Biggers Date: Tue, 9 Jun 2020 23:39:42 -0700 Subject: [PATCH] crc-t10dif: use fallback in initial state Currently the crc-t10dif module starts out with the fallback disabled and crct10dif_tfm == NULL. crc_t10dif_mod_init() tries to allocate crct10dif_tfm, and if it fails it enables the fallback. This is backwards because it means that any call to crc_t10dif() prior to module_init (which could theoretically happen from built-in code) will crash rather than use the fallback as expected. Also, it means that if the initial tfm allocation fails, then the fallback stays permanently enabled even if a crct10dif implementation is loaded later. Change it to use the more logical solution of starting with the fallback enabled, and disabling the fallback when a tfm gets allocated for the first time. This change also ends up simplifying the code. Also take the opportunity to convert the code to use the new static_key API, which is much less confusing than the old and deprecated one. Cc: Martin K. Petersen Signed-off-by: Eric Biggers Signed-off-by: Herbert Xu --- lib/crc-t10dif.c | 37 ++++++++++--------------------------- 1 file changed, 10 insertions(+), 27 deletions(-) diff --git a/lib/crc-t10dif.c b/lib/crc-t10dif.c index c9acf1c12cfc..af3613367ef9 100644 --- a/lib/crc-t10dif.c +++ b/lib/crc-t10dif.c @@ -17,7 +17,7 @@ #include static struct crypto_shash __rcu *crct10dif_tfm; -static struct static_key crct10dif_fallback __read_mostly; +static DEFINE_STATIC_KEY_TRUE(crct10dif_fallback); static DEFINE_MUTEX(crc_t10dif_mutex); static struct work_struct crct10dif_rehash_work; @@ -26,7 +26,6 @@ static int crc_t10dif_notify(struct notifier_block *self, unsigned long val, voi struct crypto_alg *alg = data; if (val != CRYPTO_MSG_ALG_LOADED || - static_key_false(&crct10dif_fallback) || strncmp(alg->cra_name, CRC_T10DIF_STRING, strlen(CRC_T10DIF_STRING))) return 0; @@ -41,10 +40,6 @@ static void crc_t10dif_rehash(struct work_struct *work) mutex_lock(&crc_t10dif_mutex); old = rcu_dereference_protected(crct10dif_tfm, lockdep_is_held(&crc_t10dif_mutex)); - if (!old) { - mutex_unlock(&crc_t10dif_mutex); - return; - } new = crypto_alloc_shash("crct10dif", 0, 0); if (IS_ERR(new)) { mutex_unlock(&crc_t10dif_mutex); @@ -53,8 +48,12 @@ static void crc_t10dif_rehash(struct work_struct *work) rcu_assign_pointer(crct10dif_tfm, new); mutex_unlock(&crc_t10dif_mutex); - synchronize_rcu(); - crypto_free_shash(old); + if (old) { + synchronize_rcu(); + crypto_free_shash(old); + } else { + static_branch_disable(&crct10dif_fallback); + } } static struct notifier_block crc_t10dif_nb = { @@ -69,7 +68,7 @@ __u16 crc_t10dif_update(__u16 crc, const unsigned char *buffer, size_t len) } desc; int err; - if (static_key_false(&crct10dif_fallback)) + if (static_branch_unlikely(&crct10dif_fallback)) return crc_t10dif_generic(crc, buffer, len); rcu_read_lock(); @@ -93,18 +92,9 @@ EXPORT_SYMBOL(crc_t10dif); static int __init crc_t10dif_mod_init(void) { - struct crypto_shash *tfm; - INIT_WORK(&crct10dif_rehash_work, crc_t10dif_rehash); crypto_register_notifier(&crc_t10dif_nb); - mutex_lock(&crc_t10dif_mutex); - tfm = crypto_alloc_shash("crct10dif", 0, 0); - if (IS_ERR(tfm)) { - static_key_slow_inc(&crct10dif_fallback); - tfm = NULL; - } - RCU_INIT_POINTER(crct10dif_tfm, tfm); - mutex_unlock(&crc_t10dif_mutex); + crc_t10dif_rehash(&crct10dif_rehash_work); return 0; } @@ -124,20 +114,13 @@ static int crc_t10dif_transform_show(char *buffer, const struct kernel_param *kp const char *name; int len; - if (static_key_false(&crct10dif_fallback)) + if (static_branch_unlikely(&crct10dif_fallback)) return sprintf(buffer, "fallback\n"); rcu_read_lock(); tfm = rcu_dereference(crct10dif_tfm); - if (!tfm) { - len = sprintf(buffer, "init\n"); - goto unlock; - } - name = crypto_tfm_alg_driver_name(crypto_shash_tfm(tfm)); len = sprintf(buffer, "%s\n", name); - -unlock: rcu_read_unlock(); return len;