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![Eric Biggers](/assets/img/avatar_default.png)
Remove support for the "Crypto usage statistics" feature (CONFIG_CRYPTO_STATS). This feature does not appear to have ever been used, and it is harmful because it significantly reduces performance and is a large maintenance burden. Covering each of these points in detail: 1. Feature is not being used Since these generic crypto statistics are only readable using netlink, it's fairly straightforward to look for programs that use them. I'm unable to find any evidence that any such programs exist. For example, Debian Code Search returns no hits except the kernel header and kernel code itself and translations of the kernel header: https://codesearch.debian.net/search?q=CRYPTOCFGA_STAT&literal=1&perpkg=1 The patch series that added this feature in 2018 (https://lore.kernel.org/linux-crypto/1537351855-16618-1-git-send-email-clabbe@baylibre.com/) said "The goal is to have an ifconfig for crypto device." This doesn't appear to have happened. It's not clear that there is real demand for crypto statistics. Just because the kernel provides other types of statistics such as I/O and networking statistics and some people find those useful does not mean that crypto statistics are useful too. Further evidence that programs are not using CONFIG_CRYPTO_STATS is that it was able to be disabled in RHEL and Fedora as a bug fix (https://gitlab.com/redhat/centos-stream/src/kernel/centos-stream-9/-/merge_requests/2947). Even further evidence comes from the fact that there are and have been bugs in how the stats work, but they were never reported. For example, before Linux v6.7 hash stats were double-counted in most cases. There has also never been any documentation for this feature, so it might be hard to use even if someone wanted to. 2. CONFIG_CRYPTO_STATS significantly reduces performance Enabling CONFIG_CRYPTO_STATS significantly reduces the performance of the crypto API, even if no program ever retrieves the statistics. This primarily affects systems with a large number of CPUs. For example, https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2039576 reported that Lustre client encryption performance improved from 21.7GB/s to 48.2GB/s by disabling CONFIG_CRYPTO_STATS. It can be argued that this means that CONFIG_CRYPTO_STATS should be optimized with per-cpu counters similar to many of the networking counters. But no one has done this in 5+ years. This is consistent with the fact that the feature appears to be unused, so there seems to be little interest in improving it as opposed to just disabling it. It can be argued that because CONFIG_CRYPTO_STATS is off by default, performance doesn't matter. But Linux distros tend to error on the side of enabling options. The option is enabled in Ubuntu and Arch Linux, and until recently was enabled in RHEL and Fedora (see above). So, even just having the option available is harmful to users. 3. CONFIG_CRYPTO_STATS is a large maintenance burden There are over 1000 lines of code associated with CONFIG_CRYPTO_STATS, spread among 32 files. It significantly complicates much of the implementation of the crypto API. After the initial submission, many fixes and refactorings have consumed effort of multiple people to keep this feature "working". We should be spending this effort elsewhere. Acked-by: Ard Biesheuvel <ardb@kernel.org> Acked-by: Corentin Labbe <clabbe@baylibre.com> Signed-off-by: Eric Biggers <ebiggers@google.com> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
222 lines
4.6 KiB
C
222 lines
4.6 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/*
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* Cryptographic API.
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*
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* RNG operations.
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*
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* Copyright (c) 2008 Neil Horman <nhorman@tuxdriver.com>
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* Copyright (c) 2015 Herbert Xu <herbert@gondor.apana.org.au>
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*/
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#include <crypto/internal/rng.h>
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#include <linux/atomic.h>
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#include <linux/cryptouser.h>
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#include <linux/err.h>
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/mutex.h>
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#include <linux/random.h>
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#include <linux/seq_file.h>
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#include <linux/slab.h>
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#include <linux/string.h>
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#include <net/netlink.h>
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#include "internal.h"
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static DEFINE_MUTEX(crypto_default_rng_lock);
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struct crypto_rng *crypto_default_rng;
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EXPORT_SYMBOL_GPL(crypto_default_rng);
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static int crypto_default_rng_refcnt;
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int crypto_rng_reset(struct crypto_rng *tfm, const u8 *seed, unsigned int slen)
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{
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u8 *buf = NULL;
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int err;
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if (!seed && slen) {
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buf = kmalloc(slen, GFP_KERNEL);
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if (!buf)
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return -ENOMEM;
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err = get_random_bytes_wait(buf, slen);
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if (err)
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goto out;
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seed = buf;
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}
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err = crypto_rng_alg(tfm)->seed(tfm, seed, slen);
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out:
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kfree_sensitive(buf);
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return err;
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}
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EXPORT_SYMBOL_GPL(crypto_rng_reset);
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static int crypto_rng_init_tfm(struct crypto_tfm *tfm)
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{
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return 0;
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}
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static unsigned int seedsize(struct crypto_alg *alg)
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{
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struct rng_alg *ralg = container_of(alg, struct rng_alg, base);
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return ralg->seedsize;
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}
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static int __maybe_unused crypto_rng_report(
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struct sk_buff *skb, struct crypto_alg *alg)
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{
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struct crypto_report_rng rrng;
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memset(&rrng, 0, sizeof(rrng));
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strscpy(rrng.type, "rng", sizeof(rrng.type));
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rrng.seedsize = seedsize(alg);
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return nla_put(skb, CRYPTOCFGA_REPORT_RNG, sizeof(rrng), &rrng);
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}
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static void crypto_rng_show(struct seq_file *m, struct crypto_alg *alg)
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__maybe_unused;
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static void crypto_rng_show(struct seq_file *m, struct crypto_alg *alg)
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{
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seq_printf(m, "type : rng\n");
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seq_printf(m, "seedsize : %u\n", seedsize(alg));
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}
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static const struct crypto_type crypto_rng_type = {
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.extsize = crypto_alg_extsize,
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.init_tfm = crypto_rng_init_tfm,
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#ifdef CONFIG_PROC_FS
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.show = crypto_rng_show,
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#endif
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#if IS_ENABLED(CONFIG_CRYPTO_USER)
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.report = crypto_rng_report,
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#endif
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.maskclear = ~CRYPTO_ALG_TYPE_MASK,
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.maskset = CRYPTO_ALG_TYPE_MASK,
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.type = CRYPTO_ALG_TYPE_RNG,
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.tfmsize = offsetof(struct crypto_rng, base),
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};
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struct crypto_rng *crypto_alloc_rng(const char *alg_name, u32 type, u32 mask)
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{
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return crypto_alloc_tfm(alg_name, &crypto_rng_type, type, mask);
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}
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EXPORT_SYMBOL_GPL(crypto_alloc_rng);
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int crypto_get_default_rng(void)
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{
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struct crypto_rng *rng;
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int err;
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mutex_lock(&crypto_default_rng_lock);
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if (!crypto_default_rng) {
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rng = crypto_alloc_rng("stdrng", 0, 0);
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err = PTR_ERR(rng);
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if (IS_ERR(rng))
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goto unlock;
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err = crypto_rng_reset(rng, NULL, crypto_rng_seedsize(rng));
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if (err) {
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crypto_free_rng(rng);
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goto unlock;
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}
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crypto_default_rng = rng;
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}
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crypto_default_rng_refcnt++;
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err = 0;
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unlock:
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mutex_unlock(&crypto_default_rng_lock);
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return err;
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}
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EXPORT_SYMBOL_GPL(crypto_get_default_rng);
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void crypto_put_default_rng(void)
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{
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mutex_lock(&crypto_default_rng_lock);
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crypto_default_rng_refcnt--;
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mutex_unlock(&crypto_default_rng_lock);
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}
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EXPORT_SYMBOL_GPL(crypto_put_default_rng);
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#if defined(CONFIG_CRYPTO_RNG) || defined(CONFIG_CRYPTO_RNG_MODULE)
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int crypto_del_default_rng(void)
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{
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int err = -EBUSY;
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mutex_lock(&crypto_default_rng_lock);
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if (crypto_default_rng_refcnt)
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goto out;
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crypto_free_rng(crypto_default_rng);
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crypto_default_rng = NULL;
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err = 0;
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out:
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mutex_unlock(&crypto_default_rng_lock);
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return err;
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}
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EXPORT_SYMBOL_GPL(crypto_del_default_rng);
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#endif
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int crypto_register_rng(struct rng_alg *alg)
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{
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struct crypto_alg *base = &alg->base;
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if (alg->seedsize > PAGE_SIZE / 8)
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return -EINVAL;
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base->cra_type = &crypto_rng_type;
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base->cra_flags &= ~CRYPTO_ALG_TYPE_MASK;
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base->cra_flags |= CRYPTO_ALG_TYPE_RNG;
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return crypto_register_alg(base);
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}
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EXPORT_SYMBOL_GPL(crypto_register_rng);
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void crypto_unregister_rng(struct rng_alg *alg)
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{
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crypto_unregister_alg(&alg->base);
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}
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EXPORT_SYMBOL_GPL(crypto_unregister_rng);
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int crypto_register_rngs(struct rng_alg *algs, int count)
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{
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int i, ret;
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for (i = 0; i < count; i++) {
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ret = crypto_register_rng(algs + i);
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if (ret)
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goto err;
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}
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return 0;
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err:
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for (--i; i >= 0; --i)
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crypto_unregister_rng(algs + i);
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return ret;
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}
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EXPORT_SYMBOL_GPL(crypto_register_rngs);
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void crypto_unregister_rngs(struct rng_alg *algs, int count)
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{
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int i;
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for (i = count - 1; i >= 0; --i)
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crypto_unregister_rng(algs + i);
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}
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EXPORT_SYMBOL_GPL(crypto_unregister_rngs);
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MODULE_LICENSE("GPL");
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MODULE_DESCRIPTION("Random Number Generator");
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