Revision 4f988f152ee087831ea5c1c77cda4454cacc052c authored by Linus Torvalds on 04 May 2012, 22:13:54 UTC, committed by Linus Torvalds on 04 May 2012, 22:13:54 UTC
The normal read_seqcount_begin() function will wait for any current writers to exit their critical region by looping until the sequence count is even. That "wait for sequence count to stabilize" is the right thing to do if the read-locker will just retry the whole operation on contention: no point in doing a potentially expensive reader sequence if we know at the beginning that we'll just end up re-doing it all. HOWEVER. Some users don't actually retry the operation, but instead will abort and do the operation with proper locking. So the sequence count case may be the optimistic quick case, but in the presense of writers you may want to do full locking in order to guarantee forward progress. The prime example of this would be the RCU name lookup. And in that case, you may well be better off without the "retry early", and are in a rush to instead get to the failure handling. Thus this "raw" interface that just returns the sequence number without testing it - it just forces the low bit to zero so that read_seqcount_retry() will always fail such a "active concurrent writer" scenario. Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 parent 2f62427
hmac.c
/*
* Cryptographic API.
*
* HMAC: Keyed-Hashing for Message Authentication (RFC2104).
*
* Copyright (c) 2002 James Morris <jmorris@intercode.com.au>
* Copyright (c) 2006 Herbert Xu <herbert@gondor.apana.org.au>
*
* The HMAC implementation is derived from USAGI.
* Copyright (c) 2002 Kazunori Miyazawa <miyazawa@linux-ipv6.org> / USAGI
*
* This program is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License as published by the Free
* Software Foundation; either version 2 of the License, or (at your option)
* any later version.
*
*/
#include <crypto/internal/hash.h>
#include <crypto/scatterwalk.h>
#include <linux/err.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/scatterlist.h>
#include <linux/string.h>
struct hmac_ctx {
struct crypto_shash *hash;
};
static inline void *align_ptr(void *p, unsigned int align)
{
return (void *)ALIGN((unsigned long)p, align);
}
static inline struct hmac_ctx *hmac_ctx(struct crypto_shash *tfm)
{
return align_ptr(crypto_shash_ctx_aligned(tfm) +
crypto_shash_statesize(tfm) * 2,
crypto_tfm_ctx_alignment());
}
static int hmac_setkey(struct crypto_shash *parent,
const u8 *inkey, unsigned int keylen)
{
int bs = crypto_shash_blocksize(parent);
int ds = crypto_shash_digestsize(parent);
int ss = crypto_shash_statesize(parent);
char *ipad = crypto_shash_ctx_aligned(parent);
char *opad = ipad + ss;
struct hmac_ctx *ctx = align_ptr(opad + ss,
crypto_tfm_ctx_alignment());
struct crypto_shash *hash = ctx->hash;
struct {
struct shash_desc shash;
char ctx[crypto_shash_descsize(hash)];
} desc;
unsigned int i;
desc.shash.tfm = hash;
desc.shash.flags = crypto_shash_get_flags(parent) &
CRYPTO_TFM_REQ_MAY_SLEEP;
if (keylen > bs) {
int err;
err = crypto_shash_digest(&desc.shash, inkey, keylen, ipad);
if (err)
return err;
keylen = ds;
} else
memcpy(ipad, inkey, keylen);
memset(ipad + keylen, 0, bs - keylen);
memcpy(opad, ipad, bs);
for (i = 0; i < bs; i++) {
ipad[i] ^= 0x36;
opad[i] ^= 0x5c;
}
return crypto_shash_init(&desc.shash) ?:
crypto_shash_update(&desc.shash, ipad, bs) ?:
crypto_shash_export(&desc.shash, ipad) ?:
crypto_shash_init(&desc.shash) ?:
crypto_shash_update(&desc.shash, opad, bs) ?:
crypto_shash_export(&desc.shash, opad);
}
static int hmac_export(struct shash_desc *pdesc, void *out)
{
struct shash_desc *desc = shash_desc_ctx(pdesc);
desc->flags = pdesc->flags & CRYPTO_TFM_REQ_MAY_SLEEP;
return crypto_shash_export(desc, out);
}
static int hmac_import(struct shash_desc *pdesc, const void *in)
{
struct shash_desc *desc = shash_desc_ctx(pdesc);
struct hmac_ctx *ctx = hmac_ctx(pdesc->tfm);
desc->tfm = ctx->hash;
desc->flags = pdesc->flags & CRYPTO_TFM_REQ_MAY_SLEEP;
return crypto_shash_import(desc, in);
}
static int hmac_init(struct shash_desc *pdesc)
{
return hmac_import(pdesc, crypto_shash_ctx_aligned(pdesc->tfm));
}
static int hmac_update(struct shash_desc *pdesc,
const u8 *data, unsigned int nbytes)
{
struct shash_desc *desc = shash_desc_ctx(pdesc);
desc->flags = pdesc->flags & CRYPTO_TFM_REQ_MAY_SLEEP;
return crypto_shash_update(desc, data, nbytes);
}
static int hmac_final(struct shash_desc *pdesc, u8 *out)
{
struct crypto_shash *parent = pdesc->tfm;
int ds = crypto_shash_digestsize(parent);
int ss = crypto_shash_statesize(parent);
char *opad = crypto_shash_ctx_aligned(parent) + ss;
struct shash_desc *desc = shash_desc_ctx(pdesc);
desc->flags = pdesc->flags & CRYPTO_TFM_REQ_MAY_SLEEP;
return crypto_shash_final(desc, out) ?:
crypto_shash_import(desc, opad) ?:
crypto_shash_finup(desc, out, ds, out);
}
static int hmac_finup(struct shash_desc *pdesc, const u8 *data,
unsigned int nbytes, u8 *out)
{
struct crypto_shash *parent = pdesc->tfm;
int ds = crypto_shash_digestsize(parent);
int ss = crypto_shash_statesize(parent);
char *opad = crypto_shash_ctx_aligned(parent) + ss;
struct shash_desc *desc = shash_desc_ctx(pdesc);
desc->flags = pdesc->flags & CRYPTO_TFM_REQ_MAY_SLEEP;
return crypto_shash_finup(desc, data, nbytes, out) ?:
crypto_shash_import(desc, opad) ?:
crypto_shash_finup(desc, out, ds, out);
}
static int hmac_init_tfm(struct crypto_tfm *tfm)
{
struct crypto_shash *parent = __crypto_shash_cast(tfm);
struct crypto_shash *hash;
struct crypto_instance *inst = (void *)tfm->__crt_alg;
struct crypto_shash_spawn *spawn = crypto_instance_ctx(inst);
struct hmac_ctx *ctx = hmac_ctx(parent);
hash = crypto_spawn_shash(spawn);
if (IS_ERR(hash))
return PTR_ERR(hash);
parent->descsize = sizeof(struct shash_desc) +
crypto_shash_descsize(hash);
ctx->hash = hash;
return 0;
}
static void hmac_exit_tfm(struct crypto_tfm *tfm)
{
struct hmac_ctx *ctx = hmac_ctx(__crypto_shash_cast(tfm));
crypto_free_shash(ctx->hash);
}
static int hmac_create(struct crypto_template *tmpl, struct rtattr **tb)
{
struct shash_instance *inst;
struct crypto_alg *alg;
struct shash_alg *salg;
int err;
int ds;
int ss;
err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_SHASH);
if (err)
return err;
salg = shash_attr_alg(tb[1], 0, 0);
if (IS_ERR(salg))
return PTR_ERR(salg);
err = -EINVAL;
ds = salg->digestsize;
ss = salg->statesize;
alg = &salg->base;
if (ds > alg->cra_blocksize ||
ss < alg->cra_blocksize)
goto out_put_alg;
inst = shash_alloc_instance("hmac", alg);
err = PTR_ERR(inst);
if (IS_ERR(inst))
goto out_put_alg;
err = crypto_init_shash_spawn(shash_instance_ctx(inst), salg,
shash_crypto_instance(inst));
if (err)
goto out_free_inst;
inst->alg.base.cra_priority = alg->cra_priority;
inst->alg.base.cra_blocksize = alg->cra_blocksize;
inst->alg.base.cra_alignmask = alg->cra_alignmask;
ss = ALIGN(ss, alg->cra_alignmask + 1);
inst->alg.digestsize = ds;
inst->alg.statesize = ss;
inst->alg.base.cra_ctxsize = sizeof(struct hmac_ctx) +
ALIGN(ss * 2, crypto_tfm_ctx_alignment());
inst->alg.base.cra_init = hmac_init_tfm;
inst->alg.base.cra_exit = hmac_exit_tfm;
inst->alg.init = hmac_init;
inst->alg.update = hmac_update;
inst->alg.final = hmac_final;
inst->alg.finup = hmac_finup;
inst->alg.export = hmac_export;
inst->alg.import = hmac_import;
inst->alg.setkey = hmac_setkey;
err = shash_register_instance(tmpl, inst);
if (err) {
out_free_inst:
shash_free_instance(shash_crypto_instance(inst));
}
out_put_alg:
crypto_mod_put(alg);
return err;
}
static struct crypto_template hmac_tmpl = {
.name = "hmac",
.create = hmac_create,
.free = shash_free_instance,
.module = THIS_MODULE,
};
static int __init hmac_module_init(void)
{
return crypto_register_template(&hmac_tmpl);
}
static void __exit hmac_module_exit(void)
{
crypto_unregister_template(&hmac_tmpl);
}
module_init(hmac_module_init);
module_exit(hmac_module_exit);
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("HMAC hash algorithm");
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