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f2d1362ff7
linux-next/lib/mpi/mpicoder.c
Nicolai Stange f2d1362ff7 lib/mpi: mpi_write_sgl(): fix skipping of leading zero limbs 
Currently, if the number of leading zeros is greater than fits into a
complete limb, mpi_write_sgl() skips them by iterating over them limb-wise.

However, it fails to adjust its internal leading zeros tracking variable,
lzeros, accordingly: it does a

  p -= sizeof(alimb);
  continue;

which should really have been a

  lzeros -= sizeof(alimb);
  continue;

Since lzeros never decreases if its initial value >= sizeof(alimb), nothing
gets copied by mpi_write_sgl() in that case.

Instead of skipping the high order zero limbs within the loop as shown
above, fix the issue by adjusting the copying loop's bounds.

Fixes: 2d4d1eea54 ("lib/mpi: Add mpi sgl helpers")
Signed-off-by: Nicolai Stange <nicstange@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2016-04-05 20:35:46 +08:00

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/* mpicoder.c - Coder for the external representation of MPIs
* Copyright (C) 1998, 1999 Free Software Foundation, Inc.
*
* This file is part of GnuPG.
*
* GnuPG 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.
*
* GnuPG is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
*/
#include <linux/bitops.h>
#include <linux/count_zeros.h>
#include "mpi-internal.h"
#define MAX_EXTERN_MPI_BITS 16384
/**
* mpi_read_raw_data - Read a raw byte stream as a positive integer
* @xbuffer: The data to read
* @nbytes: The amount of data to read
*/
MPI mpi_read_raw_data(const void *xbuffer, size_t nbytes)
{
const uint8_t *buffer = xbuffer;
int i, j;
unsigned nbits, nlimbs;
mpi_limb_t a;
MPI val = NULL;
while (nbytes > 0 && buffer[0] == 0) {
buffer++;
nbytes--;
}
nbits = nbytes * 8;
if (nbits > MAX_EXTERN_MPI_BITS) {
pr_info("MPI: mpi too large (%u bits)\n", nbits);
return NULL;
}
if (nbytes > 0)
nbits -= count_leading_zeros(buffer[0]);
else
nbits = 0;
nlimbs = DIV_ROUND_UP(nbytes, BYTES_PER_MPI_LIMB);
val = mpi_alloc(nlimbs);
if (!val)
return NULL;
val->nbits = nbits;
val->sign = 0;
val->nlimbs = nlimbs;
if (nbytes > 0) {
i = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
i %= BYTES_PER_MPI_LIMB;
for (j = nlimbs; j > 0; j--) {
a = 0;
for (; i < BYTES_PER_MPI_LIMB; i++) {
a <<= 8;
a |= *buffer++;
}
i = 0;
val->d[j - 1] = a;
}
}
return val;
}
EXPORT_SYMBOL_GPL(mpi_read_raw_data);
MPI mpi_read_from_buffer(const void *xbuffer, unsigned *ret_nread)
{
const uint8_t *buffer = xbuffer;
int i, j;
unsigned nbits, nbytes, nlimbs, nread = 0;
mpi_limb_t a;
MPI val = NULL;
if (*ret_nread < 2)
goto leave;
nbits = buffer[0] << 8 | buffer[1];
if (nbits > MAX_EXTERN_MPI_BITS) {
pr_info("MPI: mpi too large (%u bits)\n", nbits);
goto leave;
}
buffer += 2;
nread = 2;
nbytes = DIV_ROUND_UP(nbits, 8);
nlimbs = DIV_ROUND_UP(nbytes, BYTES_PER_MPI_LIMB);
val = mpi_alloc(nlimbs);
if (!val)
return NULL;
i = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
i %= BYTES_PER_MPI_LIMB;
val->nbits = nbits;
j = val->nlimbs = nlimbs;
val->sign = 0;
for (; j > 0; j--) {
a = 0;
for (; i < BYTES_PER_MPI_LIMB; i++) {
if (++nread > *ret_nread) {
printk
("MPI: mpi larger than buffer nread=%d ret_nread=%d\n",
nread, *ret_nread);
goto leave;
}
a <<= 8;
a |= *buffer++;
}
i = 0;
val->d[j - 1] = a;
}
leave:
*ret_nread = nread;
return val;
}
EXPORT_SYMBOL_GPL(mpi_read_from_buffer);
static int count_lzeros(MPI a)
{
mpi_limb_t alimb;
int i, lzeros = 0;
for (i = a->nlimbs - 1; i >= 0; i--) {
alimb = a->d[i];
if (alimb == 0) {
lzeros += sizeof(mpi_limb_t);
} else {
lzeros += count_leading_zeros(alimb) / 8;
break;
}
}
return lzeros;
}
/**
* mpi_read_buffer() - read MPI to a bufer provided by user (msb first)
*
* @a: a multi precision integer
* @buf: bufer to which the output will be written to. Needs to be at
* leaset mpi_get_size(a) long.
* @buf_len: size of the buf.
* @nbytes: receives the actual length of the data written on success and
* the data to-be-written on -EOVERFLOW in case buf_len was too
* small.
* @sign: if not NULL, it will be set to the sign of a.
*
* Return: 0 on success or error code in case of error
*/
int mpi_read_buffer(MPI a, uint8_t *buf, unsigned buf_len, unsigned *nbytes,
int *sign)
{
uint8_t *p;
mpi_limb_t alimb;
unsigned int n = mpi_get_size(a);
int i, lzeros;
if (!buf || !nbytes)
return -EINVAL;
if (sign)
*sign = a->sign;
lzeros = count_lzeros(a);
if (buf_len < n - lzeros) {
*nbytes = n - lzeros;
return -EOVERFLOW;
}
p = buf;
*nbytes = n - lzeros;
for (i = a->nlimbs - 1; i >= 0; i--) {
alimb = a->d[i];
#if BYTES_PER_MPI_LIMB == 4
*p++ = alimb >> 24;
*p++ = alimb >> 16;
*p++ = alimb >> 8;
*p++ = alimb;
#elif BYTES_PER_MPI_LIMB == 8
*p++ = alimb >> 56;
*p++ = alimb >> 48;
*p++ = alimb >> 40;
*p++ = alimb >> 32;
*p++ = alimb >> 24;
*p++ = alimb >> 16;
*p++ = alimb >> 8;
*p++ = alimb;
#else
#error please implement for this limb size.
#endif
if (lzeros > 0) {
if (lzeros >= sizeof(alimb)) {
p -= sizeof(alimb);
} else {
mpi_limb_t *limb1 = (void *)p - sizeof(alimb);
mpi_limb_t *limb2 = (void *)p - sizeof(alimb)
+ lzeros;
*limb1 = *limb2;
p -= lzeros;
}
lzeros -= sizeof(alimb);
}
}
return 0;
}
EXPORT_SYMBOL_GPL(mpi_read_buffer);
/*
* mpi_get_buffer() - Returns an allocated buffer with the MPI (msb first).
* Caller must free the return string.
* This function does return a 0 byte buffer with nbytes set to zero if the
* value of A is zero.
*
* @a: a multi precision integer.
* @nbytes: receives the length of this buffer.
* @sign: if not NULL, it will be set to the sign of the a.
*
* Return: Pointer to MPI buffer or NULL on error
*/
void *mpi_get_buffer(MPI a, unsigned *nbytes, int *sign)
{
uint8_t *buf;
unsigned int n;
int ret;
if (!nbytes)
return NULL;
n = mpi_get_size(a);
if (!n)
n++;
buf = kmalloc(n, GFP_KERNEL);
if (!buf)
return NULL;
ret = mpi_read_buffer(a, buf, n, nbytes, sign);
if (ret) {
kfree(buf);
return NULL;
}
return buf;
}
EXPORT_SYMBOL_GPL(mpi_get_buffer);
/****************
* Use BUFFER to update MPI.
*/
int mpi_set_buffer(MPI a, const void *xbuffer, unsigned nbytes, int sign)
{
const uint8_t *buffer = xbuffer, *p;
mpi_limb_t alimb;
int nlimbs;
int i;
nlimbs = DIV_ROUND_UP(nbytes, BYTES_PER_MPI_LIMB);
if (RESIZE_IF_NEEDED(a, nlimbs) < 0)
return -ENOMEM;
a->sign = sign;
for (i = 0, p = buffer + nbytes - 1; p >= buffer + BYTES_PER_MPI_LIMB;) {
#if BYTES_PER_MPI_LIMB == 4
alimb = (mpi_limb_t) *p--;
alimb |= (mpi_limb_t) *p-- << 8;
alimb |= (mpi_limb_t) *p-- << 16;
alimb |= (mpi_limb_t) *p-- << 24;
#elif BYTES_PER_MPI_LIMB == 8
alimb = (mpi_limb_t) *p--;
alimb |= (mpi_limb_t) *p-- << 8;
alimb |= (mpi_limb_t) *p-- << 16;
alimb |= (mpi_limb_t) *p-- << 24;
alimb |= (mpi_limb_t) *p-- << 32;
alimb |= (mpi_limb_t) *p-- << 40;
alimb |= (mpi_limb_t) *p-- << 48;
alimb |= (mpi_limb_t) *p-- << 56;
#else
#error please implement for this limb size.
#endif
a->d[i++] = alimb;
}
if (p >= buffer) {
#if BYTES_PER_MPI_LIMB == 4
alimb = *p--;
if (p >= buffer)
alimb |= (mpi_limb_t) *p-- << 8;
if (p >= buffer)
alimb |= (mpi_limb_t) *p-- << 16;
if (p >= buffer)
alimb |= (mpi_limb_t) *p-- << 24;
#elif BYTES_PER_MPI_LIMB == 8
alimb = (mpi_limb_t) *p--;
if (p >= buffer)
alimb |= (mpi_limb_t) *p-- << 8;
if (p >= buffer)
alimb |= (mpi_limb_t) *p-- << 16;
if (p >= buffer)
alimb |= (mpi_limb_t) *p-- << 24;
if (p >= buffer)
alimb |= (mpi_limb_t) *p-- << 32;
if (p >= buffer)
alimb |= (mpi_limb_t) *p-- << 40;
if (p >= buffer)
alimb |= (mpi_limb_t) *p-- << 48;
if (p >= buffer)
alimb |= (mpi_limb_t) *p-- << 56;
#else
#error please implement for this limb size.
#endif
a->d[i++] = alimb;
}
a->nlimbs = i;
if (i != nlimbs) {
pr_emerg("MPI: mpi_set_buffer: Assertion failed (%d != %d)", i,
nlimbs);
BUG();
}
return 0;
}
EXPORT_SYMBOL_GPL(mpi_set_buffer);
/**
* mpi_write_to_sgl() - Funnction exports MPI to an sgl (msb first)
*
* This function works in the same way as the mpi_read_buffer, but it
* takes an sgl instead of u8 * buf.
*
* @a: a multi precision integer
* @sgl: scatterlist to write to. Needs to be at least
* mpi_get_size(a) long.
* @nbytes: in/out param - it has the be set to the maximum number of
* bytes that can be written to sgl. This has to be at least
* the size of the integer a. On return it receives the actual
* length of the data written on success or the data that would
* be written if buffer was too small.
* @sign: if not NULL, it will be set to the sign of a.
*
* Return: 0 on success or error code in case of error
*/
int mpi_write_to_sgl(MPI a, struct scatterlist *sgl, unsigned *nbytes,
int *sign)
{
u8 *p, *p2;
mpi_limb_t alimb, alimb2;
unsigned int n = mpi_get_size(a);
int i, x, y = 0, lzeros, buf_len;
if (!nbytes)
return -EINVAL;
if (sign)
*sign = a->sign;
lzeros = count_lzeros(a);
if (*nbytes < n - lzeros) {
*nbytes = n - lzeros;
return -EOVERFLOW;
}
*nbytes = n - lzeros;
buf_len = sgl->length;
p2 = sg_virt(sgl);
for (i = a->nlimbs - 1 - lzeros / BYTES_PER_MPI_LIMB,
lzeros %= BYTES_PER_MPI_LIMB;
i >= 0; i--) {
alimb = a->d[i];
p = (u8 *)&alimb2;
#if BYTES_PER_MPI_LIMB == 4
*p++ = alimb >> 24;
*p++ = alimb >> 16;
*p++ = alimb >> 8;
*p++ = alimb;
#elif BYTES_PER_MPI_LIMB == 8
*p++ = alimb >> 56;
*p++ = alimb >> 48;
*p++ = alimb >> 40;
*p++ = alimb >> 32;
*p++ = alimb >> 24;
*p++ = alimb >> 16;
*p++ = alimb >> 8;
*p++ = alimb;
#else
#error please implement for this limb size.
#endif
if (lzeros > 0) {
mpi_limb_t *limb1 = (void *)p - sizeof(alimb);
mpi_limb_t *limb2 = (void *)p - sizeof(alimb)
+ lzeros;
*limb1 = *limb2;
p -= lzeros;
y = lzeros;
lzeros -= sizeof(alimb);
}
p = p - (sizeof(alimb) - y);
for (x = 0; x < sizeof(alimb) - y; x++) {
if (!buf_len) {
sgl = sg_next(sgl);
if (!sgl)
return -EINVAL;
buf_len = sgl->length;
p2 = sg_virt(sgl);
}
*p2++ = *p++;
buf_len--;
}
y = 0;
}
return 0;
}
EXPORT_SYMBOL_GPL(mpi_write_to_sgl);
/*
* mpi_read_raw_from_sgl() - Function allocates an MPI and populates it with
* data from the sgl
*
* This function works in the same way as the mpi_read_raw_data, but it
* takes an sgl instead of void * buffer. i.e. it allocates
* a new MPI and reads the content of the sgl to the MPI.
*
* @sgl: scatterlist to read from
* @len: number of bytes to read
*
* Return: Pointer to a new MPI or NULL on error
*/
MPI mpi_read_raw_from_sgl(struct scatterlist *sgl, unsigned int len)
{
struct scatterlist *sg;
int x, i, j, z, lzeros, ents;
unsigned int nbits, nlimbs, nbytes;
mpi_limb_t a;
MPI val = NULL;
lzeros = 0;
ents = sg_nents(sgl);
for_each_sg(sgl, sg, ents, i) {
const u8 *buff = sg_virt(sg);
int len = sg->length;
while (len && !*buff) {
lzeros++;
len--;
buff++;
}
if (len && *buff)
break;
ents--;
lzeros = 0;
}
sgl = sg;
if (!ents)
nbytes = 0;
else
nbytes = len - lzeros;
nbits = nbytes * 8;
if (nbits > MAX_EXTERN_MPI_BITS) {
pr_info("MPI: mpi too large (%u bits)\n", nbits);
return NULL;
}
if (nbytes > 0)
nbits -= count_leading_zeros(*(u8 *)(sg_virt(sgl) + lzeros));
else
nbits = 0;
nlimbs = DIV_ROUND_UP(nbytes, BYTES_PER_MPI_LIMB);
val = mpi_alloc(nlimbs);
if (!val)
return NULL;
val->nbits = nbits;
val->sign = 0;
val->nlimbs = nlimbs;
if (nbytes == 0)
return val;
j = nlimbs - 1;
a = 0;
z = 0;
x = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
x %= BYTES_PER_MPI_LIMB;
for_each_sg(sgl, sg, ents, i) {
const u8 *buffer = sg_virt(sg) + lzeros;
int len = sg->length - lzeros;
int buf_shift = x;
if (sg_is_last(sg) && (len % BYTES_PER_MPI_LIMB))
len += BYTES_PER_MPI_LIMB - (len % BYTES_PER_MPI_LIMB);
for (; x < len + buf_shift; x++) {
a <<= 8;
a |= *buffer++;
if (((z + x + 1) % BYTES_PER_MPI_LIMB) == 0) {
val->d[j--] = a;
a = 0;
}
}
z += x;
x = 0;
lzeros = 0;
}
return val;
}
EXPORT_SYMBOL_GPL(mpi_read_raw_from_sgl);
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