Revision 2d63ba3e41db3ceb0d23924ed2879b910276e24c authored by Linus Torvalds on 16 August 2019, 16:13:16 UTC, committed by Linus Torvalds on 16 August 2019, 16:13:16 UTC
Pull power management fixes from Rafael Wysocki:
"These add a check to avoid recent suspend-to-idle power regression on
systems with NVMe drives where the PCIe ASPM policy is "performance"
(or when the kernel is built without ASPM support), fix an issue
related to frequency limits in the schedutil cpufreq governor and fix
a mistake related to the PM QoS usage in the cpufreq core introduced
recently.
Specifics:
- Disable NVMe power optimization related to suspend-to-idle added
recently on systems where PCIe ASPM is not able to put PCIe links
into low-power states to prevent excess power from being drawn by
the system while suspended (Rafael Wysocki).
- Make the schedutil governor handle frequency limits changes
properly in all cases (Viresh Kumar).
- Prevent the cpufreq core from treating positive values returned by
dev_pm_qos_update_request() as errors (Viresh Kumar)"
* tag 'pm-5.3-rc5' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm:
nvme-pci: Allow PCI bus-level PM to be used if ASPM is disabled
PCI/ASPM: Add pcie_aspm_enabled()
cpufreq: schedutil: Don't skip freq update when limits change
cpufreq: dev_pm_qos_update_request() can return 1 on success
rsa-pkcs1pad.c
// SPDX-License-Identifier: GPL-2.0-or-later
/*
* RSA padding templates.
*
* Copyright (c) 2015 Intel Corporation
*/
#include <crypto/algapi.h>
#include <crypto/akcipher.h>
#include <crypto/internal/akcipher.h>
#include <crypto/internal/rsa.h>
#include <linux/err.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/random.h>
/*
* Hash algorithm OIDs plus ASN.1 DER wrappings [RFC4880 sec 5.2.2].
*/
static const u8 rsa_digest_info_md5[] = {
0x30, 0x20, 0x30, 0x0c, 0x06, 0x08,
0x2a, 0x86, 0x48, 0x86, 0xf7, 0x0d, 0x02, 0x05, /* OID */
0x05, 0x00, 0x04, 0x10
};
static const u8 rsa_digest_info_sha1[] = {
0x30, 0x21, 0x30, 0x09, 0x06, 0x05,
0x2b, 0x0e, 0x03, 0x02, 0x1a,
0x05, 0x00, 0x04, 0x14
};
static const u8 rsa_digest_info_rmd160[] = {
0x30, 0x21, 0x30, 0x09, 0x06, 0x05,
0x2b, 0x24, 0x03, 0x02, 0x01,
0x05, 0x00, 0x04, 0x14
};
static const u8 rsa_digest_info_sha224[] = {
0x30, 0x2d, 0x30, 0x0d, 0x06, 0x09,
0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x04,
0x05, 0x00, 0x04, 0x1c
};
static const u8 rsa_digest_info_sha256[] = {
0x30, 0x31, 0x30, 0x0d, 0x06, 0x09,
0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x01,
0x05, 0x00, 0x04, 0x20
};
static const u8 rsa_digest_info_sha384[] = {
0x30, 0x41, 0x30, 0x0d, 0x06, 0x09,
0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x02,
0x05, 0x00, 0x04, 0x30
};
static const u8 rsa_digest_info_sha512[] = {
0x30, 0x51, 0x30, 0x0d, 0x06, 0x09,
0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x03,
0x05, 0x00, 0x04, 0x40
};
static const struct rsa_asn1_template {
const char *name;
const u8 *data;
size_t size;
} rsa_asn1_templates[] = {
#define _(X) { #X, rsa_digest_info_##X, sizeof(rsa_digest_info_##X) }
_(md5),
_(sha1),
_(rmd160),
_(sha256),
_(sha384),
_(sha512),
_(sha224),
{ NULL }
#undef _
};
static const struct rsa_asn1_template *rsa_lookup_asn1(const char *name)
{
const struct rsa_asn1_template *p;
for (p = rsa_asn1_templates; p->name; p++)
if (strcmp(name, p->name) == 0)
return p;
return NULL;
}
struct pkcs1pad_ctx {
struct crypto_akcipher *child;
unsigned int key_size;
};
struct pkcs1pad_inst_ctx {
struct crypto_akcipher_spawn spawn;
const struct rsa_asn1_template *digest_info;
};
struct pkcs1pad_request {
struct scatterlist in_sg[2], out_sg[1];
uint8_t *in_buf, *out_buf;
struct akcipher_request child_req;
};
static int pkcs1pad_set_pub_key(struct crypto_akcipher *tfm, const void *key,
unsigned int keylen)
{
struct pkcs1pad_ctx *ctx = akcipher_tfm_ctx(tfm);
int err;
ctx->key_size = 0;
err = crypto_akcipher_set_pub_key(ctx->child, key, keylen);
if (err)
return err;
/* Find out new modulus size from rsa implementation */
err = crypto_akcipher_maxsize(ctx->child);
if (err > PAGE_SIZE)
return -ENOTSUPP;
ctx->key_size = err;
return 0;
}
static int pkcs1pad_set_priv_key(struct crypto_akcipher *tfm, const void *key,
unsigned int keylen)
{
struct pkcs1pad_ctx *ctx = akcipher_tfm_ctx(tfm);
int err;
ctx->key_size = 0;
err = crypto_akcipher_set_priv_key(ctx->child, key, keylen);
if (err)
return err;
/* Find out new modulus size from rsa implementation */
err = crypto_akcipher_maxsize(ctx->child);
if (err > PAGE_SIZE)
return -ENOTSUPP;
ctx->key_size = err;
return 0;
}
static unsigned int pkcs1pad_get_max_size(struct crypto_akcipher *tfm)
{
struct pkcs1pad_ctx *ctx = akcipher_tfm_ctx(tfm);
/*
* The maximum destination buffer size for the encrypt/sign operations
* will be the same as for RSA, even though it's smaller for
* decrypt/verify.
*/
return ctx->key_size;
}
static void pkcs1pad_sg_set_buf(struct scatterlist *sg, void *buf, size_t len,
struct scatterlist *next)
{
int nsegs = next ? 2 : 1;
sg_init_table(sg, nsegs);
sg_set_buf(sg, buf, len);
if (next)
sg_chain(sg, nsegs, next);
}
static int pkcs1pad_encrypt_sign_complete(struct akcipher_request *req, int err)
{
struct crypto_akcipher *tfm = crypto_akcipher_reqtfm(req);
struct pkcs1pad_ctx *ctx = akcipher_tfm_ctx(tfm);
struct pkcs1pad_request *req_ctx = akcipher_request_ctx(req);
unsigned int pad_len;
unsigned int len;
u8 *out_buf;
if (err)
goto out;
len = req_ctx->child_req.dst_len;
pad_len = ctx->key_size - len;
/* Four billion to one */
if (likely(!pad_len))
goto out;
out_buf = kzalloc(ctx->key_size, GFP_KERNEL);
err = -ENOMEM;
if (!out_buf)
goto out;
sg_copy_to_buffer(req->dst, sg_nents_for_len(req->dst, len),
out_buf + pad_len, len);
sg_copy_from_buffer(req->dst,
sg_nents_for_len(req->dst, ctx->key_size),
out_buf, ctx->key_size);
kzfree(out_buf);
out:
req->dst_len = ctx->key_size;
kfree(req_ctx->in_buf);
return err;
}
static void pkcs1pad_encrypt_sign_complete_cb(
struct crypto_async_request *child_async_req, int err)
{
struct akcipher_request *req = child_async_req->data;
struct crypto_async_request async_req;
if (err == -EINPROGRESS)
return;
async_req.data = req->base.data;
async_req.tfm = crypto_akcipher_tfm(crypto_akcipher_reqtfm(req));
async_req.flags = child_async_req->flags;
req->base.complete(&async_req,
pkcs1pad_encrypt_sign_complete(req, err));
}
static int pkcs1pad_encrypt(struct akcipher_request *req)
{
struct crypto_akcipher *tfm = crypto_akcipher_reqtfm(req);
struct pkcs1pad_ctx *ctx = akcipher_tfm_ctx(tfm);
struct pkcs1pad_request *req_ctx = akcipher_request_ctx(req);
int err;
unsigned int i, ps_end;
if (!ctx->key_size)
return -EINVAL;
if (req->src_len > ctx->key_size - 11)
return -EOVERFLOW;
if (req->dst_len < ctx->key_size) {
req->dst_len = ctx->key_size;
return -EOVERFLOW;
}
req_ctx->in_buf = kmalloc(ctx->key_size - 1 - req->src_len,
GFP_KERNEL);
if (!req_ctx->in_buf)
return -ENOMEM;
ps_end = ctx->key_size - req->src_len - 2;
req_ctx->in_buf[0] = 0x02;
for (i = 1; i < ps_end; i++)
req_ctx->in_buf[i] = 1 + prandom_u32_max(255);
req_ctx->in_buf[ps_end] = 0x00;
pkcs1pad_sg_set_buf(req_ctx->in_sg, req_ctx->in_buf,
ctx->key_size - 1 - req->src_len, req->src);
akcipher_request_set_tfm(&req_ctx->child_req, ctx->child);
akcipher_request_set_callback(&req_ctx->child_req, req->base.flags,
pkcs1pad_encrypt_sign_complete_cb, req);
/* Reuse output buffer */
akcipher_request_set_crypt(&req_ctx->child_req, req_ctx->in_sg,
req->dst, ctx->key_size - 1, req->dst_len);
err = crypto_akcipher_encrypt(&req_ctx->child_req);
if (err != -EINPROGRESS && err != -EBUSY)
return pkcs1pad_encrypt_sign_complete(req, err);
return err;
}
static int pkcs1pad_decrypt_complete(struct akcipher_request *req, int err)
{
struct crypto_akcipher *tfm = crypto_akcipher_reqtfm(req);
struct pkcs1pad_ctx *ctx = akcipher_tfm_ctx(tfm);
struct pkcs1pad_request *req_ctx = akcipher_request_ctx(req);
unsigned int dst_len;
unsigned int pos;
u8 *out_buf;
if (err)
goto done;
err = -EINVAL;
dst_len = req_ctx->child_req.dst_len;
if (dst_len < ctx->key_size - 1)
goto done;
out_buf = req_ctx->out_buf;
if (dst_len == ctx->key_size) {
if (out_buf[0] != 0x00)
/* Decrypted value had no leading 0 byte */
goto done;
dst_len--;
out_buf++;
}
if (out_buf[0] != 0x02)
goto done;
for (pos = 1; pos < dst_len; pos++)
if (out_buf[pos] == 0x00)
break;
if (pos < 9 || pos == dst_len)
goto done;
pos++;
err = 0;
if (req->dst_len < dst_len - pos)
err = -EOVERFLOW;
req->dst_len = dst_len - pos;
if (!err)
sg_copy_from_buffer(req->dst,
sg_nents_for_len(req->dst, req->dst_len),
out_buf + pos, req->dst_len);
done:
kzfree(req_ctx->out_buf);
return err;
}
static void pkcs1pad_decrypt_complete_cb(
struct crypto_async_request *child_async_req, int err)
{
struct akcipher_request *req = child_async_req->data;
struct crypto_async_request async_req;
if (err == -EINPROGRESS)
return;
async_req.data = req->base.data;
async_req.tfm = crypto_akcipher_tfm(crypto_akcipher_reqtfm(req));
async_req.flags = child_async_req->flags;
req->base.complete(&async_req, pkcs1pad_decrypt_complete(req, err));
}
static int pkcs1pad_decrypt(struct akcipher_request *req)
{
struct crypto_akcipher *tfm = crypto_akcipher_reqtfm(req);
struct pkcs1pad_ctx *ctx = akcipher_tfm_ctx(tfm);
struct pkcs1pad_request *req_ctx = akcipher_request_ctx(req);
int err;
if (!ctx->key_size || req->src_len != ctx->key_size)
return -EINVAL;
req_ctx->out_buf = kmalloc(ctx->key_size, GFP_KERNEL);
if (!req_ctx->out_buf)
return -ENOMEM;
pkcs1pad_sg_set_buf(req_ctx->out_sg, req_ctx->out_buf,
ctx->key_size, NULL);
akcipher_request_set_tfm(&req_ctx->child_req, ctx->child);
akcipher_request_set_callback(&req_ctx->child_req, req->base.flags,
pkcs1pad_decrypt_complete_cb, req);
/* Reuse input buffer, output to a new buffer */
akcipher_request_set_crypt(&req_ctx->child_req, req->src,
req_ctx->out_sg, req->src_len,
ctx->key_size);
err = crypto_akcipher_decrypt(&req_ctx->child_req);
if (err != -EINPROGRESS && err != -EBUSY)
return pkcs1pad_decrypt_complete(req, err);
return err;
}
static int pkcs1pad_sign(struct akcipher_request *req)
{
struct crypto_akcipher *tfm = crypto_akcipher_reqtfm(req);
struct pkcs1pad_ctx *ctx = akcipher_tfm_ctx(tfm);
struct pkcs1pad_request *req_ctx = akcipher_request_ctx(req);
struct akcipher_instance *inst = akcipher_alg_instance(tfm);
struct pkcs1pad_inst_ctx *ictx = akcipher_instance_ctx(inst);
const struct rsa_asn1_template *digest_info = ictx->digest_info;
int err;
unsigned int ps_end, digest_size = 0;
if (!ctx->key_size)
return -EINVAL;
if (digest_info)
digest_size = digest_info->size;
if (req->src_len + digest_size > ctx->key_size - 11)
return -EOVERFLOW;
if (req->dst_len < ctx->key_size) {
req->dst_len = ctx->key_size;
return -EOVERFLOW;
}
req_ctx->in_buf = kmalloc(ctx->key_size - 1 - req->src_len,
GFP_KERNEL);
if (!req_ctx->in_buf)
return -ENOMEM;
ps_end = ctx->key_size - digest_size - req->src_len - 2;
req_ctx->in_buf[0] = 0x01;
memset(req_ctx->in_buf + 1, 0xff, ps_end - 1);
req_ctx->in_buf[ps_end] = 0x00;
if (digest_info)
memcpy(req_ctx->in_buf + ps_end + 1, digest_info->data,
digest_info->size);
pkcs1pad_sg_set_buf(req_ctx->in_sg, req_ctx->in_buf,
ctx->key_size - 1 - req->src_len, req->src);
akcipher_request_set_tfm(&req_ctx->child_req, ctx->child);
akcipher_request_set_callback(&req_ctx->child_req, req->base.flags,
pkcs1pad_encrypt_sign_complete_cb, req);
/* Reuse output buffer */
akcipher_request_set_crypt(&req_ctx->child_req, req_ctx->in_sg,
req->dst, ctx->key_size - 1, req->dst_len);
err = crypto_akcipher_decrypt(&req_ctx->child_req);
if (err != -EINPROGRESS && err != -EBUSY)
return pkcs1pad_encrypt_sign_complete(req, err);
return err;
}
static int pkcs1pad_verify_complete(struct akcipher_request *req, int err)
{
struct crypto_akcipher *tfm = crypto_akcipher_reqtfm(req);
struct pkcs1pad_ctx *ctx = akcipher_tfm_ctx(tfm);
struct pkcs1pad_request *req_ctx = akcipher_request_ctx(req);
struct akcipher_instance *inst = akcipher_alg_instance(tfm);
struct pkcs1pad_inst_ctx *ictx = akcipher_instance_ctx(inst);
const struct rsa_asn1_template *digest_info = ictx->digest_info;
unsigned int dst_len;
unsigned int pos;
u8 *out_buf;
if (err)
goto done;
err = -EINVAL;
dst_len = req_ctx->child_req.dst_len;
if (dst_len < ctx->key_size - 1)
goto done;
out_buf = req_ctx->out_buf;
if (dst_len == ctx->key_size) {
if (out_buf[0] != 0x00)
/* Decrypted value had no leading 0 byte */
goto done;
dst_len--;
out_buf++;
}
err = -EBADMSG;
if (out_buf[0] != 0x01)
goto done;
for (pos = 1; pos < dst_len; pos++)
if (out_buf[pos] != 0xff)
break;
if (pos < 9 || pos == dst_len || out_buf[pos] != 0x00)
goto done;
pos++;
if (digest_info) {
if (crypto_memneq(out_buf + pos, digest_info->data,
digest_info->size))
goto done;
pos += digest_info->size;
}
err = 0;
if (req->dst_len != dst_len - pos) {
err = -EKEYREJECTED;
req->dst_len = dst_len - pos;
goto done;
}
/* Extract appended digest. */
sg_pcopy_to_buffer(req->src,
sg_nents_for_len(req->src,
req->src_len + req->dst_len),
req_ctx->out_buf + ctx->key_size,
req->dst_len, ctx->key_size);
/* Do the actual verification step. */
if (memcmp(req_ctx->out_buf + ctx->key_size, out_buf + pos,
req->dst_len) != 0)
err = -EKEYREJECTED;
done:
kzfree(req_ctx->out_buf);
return err;
}
static void pkcs1pad_verify_complete_cb(
struct crypto_async_request *child_async_req, int err)
{
struct akcipher_request *req = child_async_req->data;
struct crypto_async_request async_req;
if (err == -EINPROGRESS)
return;
async_req.data = req->base.data;
async_req.tfm = crypto_akcipher_tfm(crypto_akcipher_reqtfm(req));
async_req.flags = child_async_req->flags;
req->base.complete(&async_req, pkcs1pad_verify_complete(req, err));
}
/*
* The verify operation is here for completeness similar to the verification
* defined in RFC2313 section 10.2 except that block type 0 is not accepted,
* as in RFC2437. RFC2437 section 9.2 doesn't define any operation to
* retrieve the DigestInfo from a signature, instead the user is expected
* to call the sign operation to generate the expected signature and compare
* signatures instead of the message-digests.
*/
static int pkcs1pad_verify(struct akcipher_request *req)
{
struct crypto_akcipher *tfm = crypto_akcipher_reqtfm(req);
struct pkcs1pad_ctx *ctx = akcipher_tfm_ctx(tfm);
struct pkcs1pad_request *req_ctx = akcipher_request_ctx(req);
int err;
if (WARN_ON(req->dst) ||
WARN_ON(!req->dst_len) ||
!ctx->key_size || req->src_len < ctx->key_size)
return -EINVAL;
req_ctx->out_buf = kmalloc(ctx->key_size + req->dst_len, GFP_KERNEL);
if (!req_ctx->out_buf)
return -ENOMEM;
pkcs1pad_sg_set_buf(req_ctx->out_sg, req_ctx->out_buf,
ctx->key_size, NULL);
akcipher_request_set_tfm(&req_ctx->child_req, ctx->child);
akcipher_request_set_callback(&req_ctx->child_req, req->base.flags,
pkcs1pad_verify_complete_cb, req);
/* Reuse input buffer, output to a new buffer */
akcipher_request_set_crypt(&req_ctx->child_req, req->src,
req_ctx->out_sg, req->src_len,
ctx->key_size);
err = crypto_akcipher_encrypt(&req_ctx->child_req);
if (err != -EINPROGRESS && err != -EBUSY)
return pkcs1pad_verify_complete(req, err);
return err;
}
static int pkcs1pad_init_tfm(struct crypto_akcipher *tfm)
{
struct akcipher_instance *inst = akcipher_alg_instance(tfm);
struct pkcs1pad_inst_ctx *ictx = akcipher_instance_ctx(inst);
struct pkcs1pad_ctx *ctx = akcipher_tfm_ctx(tfm);
struct crypto_akcipher *child_tfm;
child_tfm = crypto_spawn_akcipher(&ictx->spawn);
if (IS_ERR(child_tfm))
return PTR_ERR(child_tfm);
ctx->child = child_tfm;
return 0;
}
static void pkcs1pad_exit_tfm(struct crypto_akcipher *tfm)
{
struct pkcs1pad_ctx *ctx = akcipher_tfm_ctx(tfm);
crypto_free_akcipher(ctx->child);
}
static void pkcs1pad_free(struct akcipher_instance *inst)
{
struct pkcs1pad_inst_ctx *ctx = akcipher_instance_ctx(inst);
struct crypto_akcipher_spawn *spawn = &ctx->spawn;
crypto_drop_akcipher(spawn);
kfree(inst);
}
static int pkcs1pad_create(struct crypto_template *tmpl, struct rtattr **tb)
{
const struct rsa_asn1_template *digest_info;
struct crypto_attr_type *algt;
struct akcipher_instance *inst;
struct pkcs1pad_inst_ctx *ctx;
struct crypto_akcipher_spawn *spawn;
struct akcipher_alg *rsa_alg;
const char *rsa_alg_name;
const char *hash_name;
int err;
algt = crypto_get_attr_type(tb);
if (IS_ERR(algt))
return PTR_ERR(algt);
if ((algt->type ^ CRYPTO_ALG_TYPE_AKCIPHER) & algt->mask)
return -EINVAL;
rsa_alg_name = crypto_attr_alg_name(tb[1]);
if (IS_ERR(rsa_alg_name))
return PTR_ERR(rsa_alg_name);
hash_name = crypto_attr_alg_name(tb[2]);
if (IS_ERR(hash_name))
hash_name = NULL;
if (hash_name) {
digest_info = rsa_lookup_asn1(hash_name);
if (!digest_info)
return -EINVAL;
} else
digest_info = NULL;
inst = kzalloc(sizeof(*inst) + sizeof(*ctx), GFP_KERNEL);
if (!inst)
return -ENOMEM;
ctx = akcipher_instance_ctx(inst);
spawn = &ctx->spawn;
ctx->digest_info = digest_info;
crypto_set_spawn(&spawn->base, akcipher_crypto_instance(inst));
err = crypto_grab_akcipher(spawn, rsa_alg_name, 0,
crypto_requires_sync(algt->type, algt->mask));
if (err)
goto out_free_inst;
rsa_alg = crypto_spawn_akcipher_alg(spawn);
err = -ENAMETOOLONG;
if (!hash_name) {
if (snprintf(inst->alg.base.cra_name,
CRYPTO_MAX_ALG_NAME, "pkcs1pad(%s)",
rsa_alg->base.cra_name) >= CRYPTO_MAX_ALG_NAME)
goto out_drop_alg;
if (snprintf(inst->alg.base.cra_driver_name,
CRYPTO_MAX_ALG_NAME, "pkcs1pad(%s)",
rsa_alg->base.cra_driver_name) >=
CRYPTO_MAX_ALG_NAME)
goto out_drop_alg;
} else {
if (snprintf(inst->alg.base.cra_name, CRYPTO_MAX_ALG_NAME,
"pkcs1pad(%s,%s)", rsa_alg->base.cra_name,
hash_name) >= CRYPTO_MAX_ALG_NAME)
goto out_drop_alg;
if (snprintf(inst->alg.base.cra_driver_name,
CRYPTO_MAX_ALG_NAME, "pkcs1pad(%s,%s)",
rsa_alg->base.cra_driver_name,
hash_name) >= CRYPTO_MAX_ALG_NAME)
goto out_drop_alg;
}
inst->alg.base.cra_flags = rsa_alg->base.cra_flags & CRYPTO_ALG_ASYNC;
inst->alg.base.cra_priority = rsa_alg->base.cra_priority;
inst->alg.base.cra_ctxsize = sizeof(struct pkcs1pad_ctx);
inst->alg.init = pkcs1pad_init_tfm;
inst->alg.exit = pkcs1pad_exit_tfm;
inst->alg.encrypt = pkcs1pad_encrypt;
inst->alg.decrypt = pkcs1pad_decrypt;
inst->alg.sign = pkcs1pad_sign;
inst->alg.verify = pkcs1pad_verify;
inst->alg.set_pub_key = pkcs1pad_set_pub_key;
inst->alg.set_priv_key = pkcs1pad_set_priv_key;
inst->alg.max_size = pkcs1pad_get_max_size;
inst->alg.reqsize = sizeof(struct pkcs1pad_request) + rsa_alg->reqsize;
inst->free = pkcs1pad_free;
err = akcipher_register_instance(tmpl, inst);
if (err)
goto out_drop_alg;
return 0;
out_drop_alg:
crypto_drop_akcipher(spawn);
out_free_inst:
kfree(inst);
return err;
}
struct crypto_template rsa_pkcs1pad_tmpl = {
.name = "pkcs1pad",
.create = pkcs1pad_create,
.module = THIS_MODULE,
};
Computing file changes ...
