Commit 01d798e9 authored by Haixin Xu's avatar Haixin Xu Committed by Herbert Xu
Browse files

crypto: jitterentropy - replace long-held spinlock with mutex 



jent_kcapi_random() serializes the shared jitterentropy state, but it
currently holds a spinlock across the jent_read_entropy() call. That
path performs expensive jitter collection and SHA3 conditioning, so
parallel readers can trigger stalls as contending waiters spin for
the same lock.

To prevent non-preemptible lock hold, replace rng->jent_lock with a
mutex so contended readers sleep instead of spinning on a shared lock
held across expensive entropy generation.

Fixes: bb5530e4 ("crypto: jitterentropy - add jitterentropy RNG")
Reported-by: default avatarYifan Wu <yifanwucs@gmail.com>
Reported-by: default avatarJuefei Pu <tomapufckgml@gmail.com>
Reported-by: default avatarYuan Tan <yuantan098@gmail.com>
Suggested-by: default avatarXin Liu <bird@lzu.edu.cn>
Signed-off-by: default avatarHaixin Xu <jerryxucs@gmail.com>
Reviewed-by: default avatarStephan Mueller <smueller@chronox.de>
Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
parent 06c42142

crypto/jitterentropy-kcapi.c

+7 −7
Original line number Diff line number Diff line
@@ -42,6 +42,7 @@ 
#include <linux/fips.h>

#include <linux/kernel.h>

#include <linux/module.h>

#include <linux/mutex.h>

#include <linux/slab.h>

#include <linux/time.h>

#include <crypto/internal/rng.h>
@@ -193,7 +194,7 @@ int jent_read_random_block(void *hash_state, char *dst, unsigned int dst_len) 
 ***************************************************************************/



struct jitterentropy {

	spinlock_t jent_lock;

	struct mutex jent_lock;

	struct rand_data *entropy_collector;

	struct crypto_shash *tfm;

	struct shash_desc *sdesc;
@@ -203,7 +204,7 @@ static void jent_kcapi_cleanup(struct crypto_tfm *tfm) 
{

	struct jitterentropy *rng = crypto_tfm_ctx(tfm);



	spin_lock(&rng->jent_lock);

	mutex_lock(&rng->jent_lock);



	if (rng->sdesc) {

		shash_desc_zero(rng->sdesc);
@@ -218,7 +219,7 @@ static void jent_kcapi_cleanup(struct crypto_tfm *tfm) 
	if (rng->entropy_collector)

		jent_entropy_collector_free(rng->entropy_collector);

	rng->entropy_collector = NULL;

	spin_unlock(&rng->jent_lock);

	mutex_unlock(&rng->jent_lock);

}



static int jent_kcapi_init(struct crypto_tfm *tfm)
@@ -228,7 +229,7 @@ static int jent_kcapi_init(struct crypto_tfm *tfm) 
	struct shash_desc *sdesc;

	int size, ret = 0;



	spin_lock_init(&rng->jent_lock);

	mutex_init(&rng->jent_lock);



	/* Use SHA3-256 as conditioner */

	hash = crypto_alloc_shash(JENT_CONDITIONING_HASH, 0, 0);
@@ -257,7 +258,6 @@ static int jent_kcapi_init(struct crypto_tfm *tfm) 
		goto err;

	}



	spin_lock_init(&rng->jent_lock);

	return 0;



err:
@@ -272,7 +272,7 @@ static int jent_kcapi_random(struct crypto_rng *tfm, 
	struct jitterentropy *rng = crypto_rng_ctx(tfm);

	int ret = 0;



	spin_lock(&rng->jent_lock);

	mutex_lock(&rng->jent_lock);



	ret = jent_read_entropy(rng->entropy_collector, rdata, dlen);
@@ -298,7 +298,7 @@ static int jent_kcapi_random(struct crypto_rng *tfm, 
		ret = -EINVAL;

	}



	spin_unlock(&rng->jent_lock);

	mutex_unlock(&rng->jent_lock);



	return ret;

}