crypto: api - Add crypto_tfm_get

Add a crypto_tfm_get interface to allow tfm objects to be shared.
They can still be freed in the usual way.

This should only be done with tfm objects with no keys.  You must
also not modify the tfm flags in any way once it becomes shared.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/api.c

@@ -408,6 +408,7 @@ struct crypto_tfm *__crypto_alloc_tfm(struct crypto_alg *alg, u32 type,
 		goto out_err;
 
 	tfm->__crt_alg = alg;
+	refcount_set(&tfm->refcnt, 1);
 
 	err = crypto_init_ops(tfm, type, mask);
 	if (err)
@@ -507,6 +508,7 @@ void *crypto_create_tfm_node(struct crypto_alg *alg,
 	tfm = (struct crypto_tfm *)(mem + tfmsize);
 	tfm->__crt_alg = alg;
 	tfm->node = node;
+	refcount_set(&tfm->refcnt, 1);
 
 	err = frontend->init_tfm(tfm);
 	if (err)
@@ -619,6 +621,8 @@ void crypto_destroy_tfm(void *mem, struct crypto_tfm *tfm)
 	if (IS_ERR_OR_NULL(mem))
 		return;
 
+	if (!refcount_dec_and_test(&tfm->refcnt))
+		return;
 	alg = tfm->__crt_alg;
 
 	if (!tfm->exit && alg->cra_exit)

crypto/internal.h

@@ -10,6 +10,7 @@
 
 #include <crypto/algapi.h>
 #include <linux/completion.h>
+#include <linux/err.h>
 #include <linux/jump_label.h>
 #include <linux/list.h>
 #include <linux/module.h>
@@ -186,5 +187,10 @@ static inline int crypto_is_test_larval(struct crypto_larval *larval)
 	return larval->alg.cra_driver_name[0];
 }
 
+static inline struct crypto_tfm *crypto_tfm_get(struct crypto_tfm *tfm)
+{
+	return refcount_inc_not_zero(&tfm->refcnt) ? tfm : ERR_PTR(-EOVERFLOW);
+}
+
 #endif	/* _CRYPTO_INTERNAL_H */
 

include/linux/crypto.h

@@ -419,6 +419,7 @@ int crypto_has_alg(const char *name, u32 type, u32 mask);
  */
 
 struct crypto_tfm {
+	refcount_t refcnt;
 
 	u32 crt_flags;