[PATCH 0/2] crc-t10dif library improvements

[PATCH 0/2] crc-t10dif library improvements

[Eric Biggers]

This series makes some more improvements to lib/crc-t10dif.c, as discussed at
https://lkml.kernel.org/linux-crypto/20200604063324.GA28813@gondor.apana.org.au/T/#u

This applies on top of Herbert's
"[v2 PATCH] crc-t10dif: Fix potential crypto notify dead-lock".

Eric Biggers (2):
  crc-t10dif: use fallback in initial state
  crc-t10dif: clean up some more things

 lib/crc-t10dif.c | 61 +++++++++++++++++-------------------------------
 1 file changed, 21 insertions(+), 40 deletions(-)

-- 
2.26.2

[PATCH 1/2] crc-t10dif: use fallback in initial state

[Eric Biggers]

From: Eric Biggers <ebiggers@google.com>

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 <martin.petersen@oracle.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 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 c9acf1c12cfcb4..af3613367ef944 100644
--- a/lib/crc-t10dif.c
+++ b/lib/crc-t10dif.c
@@ -17,7 +17,7 @@
 #include <linux/notifier.h>
 
 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;
-- 
2.26.2

[PATCH 2/2] crc-t10dif: clean up some more things

[Eric Biggers]

From: Eric Biggers <ebiggers@google.com>

- Correctly compare the algorithm name in crc_t10dif_notify().

- Use proper NOTIFY_* status codes instead of 0.

- Consistently use CRC_T10DIF_STRING instead of "crct10dif" directly.

- Use a proper type for the shash_desc context.

- Use crypto_shash_driver_name() instead of open-coding it.

- Make crc_t10dif_transform_show() use snprintf() rather than sprintf().
  This isn't actually necessary since the buffer has size PAGE_SIZE
  and CRYPTO_MAX_ALG_NAME < PAGE_SIZE, but it's good practice.

- Give the "transform" sysfs file mode 0444 rather than 0644,
  since it doesn't implement a setter method.

- Adjust the module description to not be the same as crct10dif-generic.

Cc: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 lib/crc-t10dif.c | 24 +++++++++++-------------
 1 file changed, 11 insertions(+), 13 deletions(-)

diff --git a/lib/crc-t10dif.c b/lib/crc-t10dif.c
index af3613367ef944..1ed2ed4870971e 100644
--- a/lib/crc-t10dif.c
+++ b/lib/crc-t10dif.c
@@ -26,11 +26,11 @@ static int crc_t10dif_notify(struct notifier_block *self, unsigned long val, voi
 	struct crypto_alg *alg = data;
 
 	if (val != CRYPTO_MSG_ALG_LOADED ||
-	    strncmp(alg->cra_name, CRC_T10DIF_STRING, strlen(CRC_T10DIF_STRING)))
-		return 0;
+	    strcmp(alg->cra_name, CRC_T10DIF_STRING))
+		return NOTIFY_DONE;
 
 	schedule_work(&crct10dif_rehash_work);
-	return 0;
+	return NOTIFY_OK;
 }
 
 static void crc_t10dif_rehash(struct work_struct *work)
@@ -40,7 +40,7 @@ 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));
-	new = crypto_alloc_shash("crct10dif", 0, 0);
+	new = crypto_alloc_shash(CRC_T10DIF_STRING, 0, 0);
 	if (IS_ERR(new)) {
 		mutex_unlock(&crc_t10dif_mutex);
 		return;
@@ -64,7 +64,7 @@ __u16 crc_t10dif_update(__u16 crc, const unsigned char *buffer, size_t len)
 {
 	struct {
 		struct shash_desc shash;
-		char ctx[2];
+		__u16 crc;
 	} desc;
 	int err;
 
@@ -73,14 +73,13 @@ __u16 crc_t10dif_update(__u16 crc, const unsigned char *buffer, size_t len)
 
 	rcu_read_lock();
 	desc.shash.tfm = rcu_dereference(crct10dif_tfm);
-	*(__u16 *)desc.ctx = crc;
-
+	desc.crc = crc;
 	err = crypto_shash_update(&desc.shash, buffer, len);
 	rcu_read_unlock();
 
 	BUG_ON(err);
 
-	return *(__u16 *)desc.ctx;
+	return desc.crc;
 }
 EXPORT_SYMBOL(crc_t10dif_update);
 
@@ -111,7 +110,6 @@ module_exit(crc_t10dif_mod_fini);
 static int crc_t10dif_transform_show(char *buffer, const struct kernel_param *kp)
 {
 	struct crypto_shash *tfm;
-	const char *name;
 	int len;
 
 	if (static_branch_unlikely(&crct10dif_fallback))
@@ -119,15 +117,15 @@ static int crc_t10dif_transform_show(char *buffer, const struct kernel_param *kp
 
 	rcu_read_lock();
 	tfm = rcu_dereference(crct10dif_tfm);
-	name = crypto_tfm_alg_driver_name(crypto_shash_tfm(tfm));
-	len = sprintf(buffer, "%s\n", name);
+	len = snprintf(buffer, PAGE_SIZE, "%s\n",
+		       crypto_shash_driver_name(tfm));
 	rcu_read_unlock();
 
 	return len;
 }
 
-module_param_call(transform, NULL, crc_t10dif_transform_show, NULL, 0644);
+module_param_call(transform, NULL, crc_t10dif_transform_show, NULL, 0444);
 
-MODULE_DESCRIPTION("T10 DIF CRC calculation");
+MODULE_DESCRIPTION("T10 DIF CRC calculation (library API)");
 MODULE_LICENSE("GPL");
 MODULE_SOFTDEP("pre: crct10dif");
-- 
2.26.2

Re: [PATCH 0/2] crc-t10dif library improvements

[Herbert Xu]

Eric Biggers <ebiggers@kernel.org> wrote:
> This series makes some more improvements to lib/crc-t10dif.c, as discussed at
> https://lkml.kernel.org/linux-crypto/20200604063324.GA28813@gondor.apana.org.au/T/#u
> 
> This applies on top of Herbert's
> "[v2 PATCH] crc-t10dif: Fix potential crypto notify dead-lock".
> 
> Eric Biggers (2):
>  crc-t10dif: use fallback in initial state
>  crc-t10dif: clean up some more things
> 
> lib/crc-t10dif.c | 61 +++++++++++++++++-------------------------------
> 1 file changed, 21 insertions(+), 40 deletions(-)

All applied.  Thanks.
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt