pidgin/pidgin

certificate: Use public key fingerprint to compare certificates
release-2.x.y
2017-03-07, dx
887efbd652d8
certificate: Use public key fingerprint to compare certificates

This fixes an issue with google talk's certificates and gnutls, where the root
certificate in the provided chain is a slightly different version of the one
that is usually present in the certificate stores, but the SubjectPublicKeyInfo
section is the same.

This adds a PurpleCertificateScheme function, compare_pubkeys, and its wrapper
purple_certificate_compare_pubkeys().

This is only implemented for gnutls, since the NSS plugin only uses the NSS
certificate validation code. Even if that path was reachable from a plugin that
doesn't implement this method, it would return FALSE and behave as if this bug
was never fixed.

The gnutls implementation uses the gnutls_x509_crt_get_key_id() function,
which returns a hash of the SubjectPublicKeyInfo section of the certificate.

In gnutls versions older than 3.4.1, this may be a SHA1 hash, but after that
version SHA256 support was added (without much fanfare - the documentation
barely mentions this at all), and we just use the constant for the best known
algo, which for current versions is just SHA256. Older versions ignore that
flag parameter.

The whole comparison is modeled after the private _gnutls_check_if_same_key(),
which checks if both certificates have the same DN ("unique id") and does a
memcmp() of the raw SPKI section. We don't have direct access to the raw SPKI
section but comparing their fingerprints is good enough.
/*
* @file circbuffer.h Buffer Utility Functions
* @ingroup core
*/
/* Purple is the legal property of its developers, whose names are too numerous
* to list here. Please refer to the COPYRIGHT file distributed with this
* source distribution.
*
* 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.
*
* This program 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., 51 Franklin Street, Fifth Floor, Boston, MA 02111-1301 USA
*/
#include "internal.h"
#include "circbuffer.h"
#define DEFAULT_BUF_SIZE 256
PurpleCircBuffer *
purple_circ_buffer_new(gsize growsize) {
PurpleCircBuffer *buf = g_new0(PurpleCircBuffer, 1);
buf->growsize = growsize ? growsize : DEFAULT_BUF_SIZE;
return buf;
}
void purple_circ_buffer_destroy(PurpleCircBuffer *buf) {
g_return_if_fail(buf != NULL);
g_free(buf->buffer);
g_free(buf);
}
static void grow_circ_buffer(PurpleCircBuffer *buf, gsize len) {
gsize in_offset = 0, out_offset = 0;
gsize start_buflen;
g_return_if_fail(buf != NULL);
start_buflen = buf->buflen;
while ((buf->buflen - buf->bufused) < len)
buf->buflen += buf->growsize;
if (buf->inptr != NULL) {
in_offset = buf->inptr - buf->buffer;
out_offset = buf->outptr - buf->buffer;
}
buf->buffer = g_realloc(buf->buffer, buf->buflen);
/* adjust the fill and remove pointer locations */
if (buf->inptr == NULL) {
buf->inptr = buf->outptr = buf->buffer;
} else {
buf->inptr = buf->buffer + in_offset;
buf->outptr = buf->buffer + out_offset;
}
/* If the fill pointer is wrapped to before the remove
* pointer, we need to shift the data */
if (in_offset < out_offset
|| (in_offset == out_offset && buf->bufused > 0)) {
gsize shift_n = MIN(buf->buflen - start_buflen, in_offset);
memcpy(buf->buffer + start_buflen, buf->buffer, shift_n);
/* If we couldn't fit the wrapped read buffer
* at the end */
if (shift_n < in_offset) {
memmove(buf->buffer,
buf->buffer + shift_n,
in_offset - shift_n);
buf->inptr = buf->buffer +
(in_offset - shift_n);
} else {
buf->inptr = buf->buffer +
start_buflen + in_offset;
}
}
}
void purple_circ_buffer_append(PurpleCircBuffer *buf, gconstpointer src, gsize len) {
gsize len_stored;
g_return_if_fail(buf != NULL);
/* Grow the buffer, if necessary */
if ((buf->buflen - buf->bufused) < len)
grow_circ_buffer(buf, len);
/* If there is not enough room to copy all of src before hitting
* the end of the buffer then we will need to do two copies.
* One copy from inptr to the end of the buffer, and the
* second copy from the start of the buffer to the end of src. */
if (buf->inptr >= buf->outptr)
len_stored = MIN(len, buf->buflen - (buf->inptr - buf->buffer));
else
len_stored = len;
if (len_stored > 0)
memcpy(buf->inptr, src, len_stored);
if (len_stored < len) {
memcpy(buf->buffer, (char*)src + len_stored, len - len_stored);
buf->inptr = buf->buffer + (len - len_stored);
} else {
buf->inptr += len_stored;
}
buf->bufused += len;
}
gsize purple_circ_buffer_get_max_read(const PurpleCircBuffer *buf) {
gsize max_read;
g_return_val_if_fail(buf != NULL, 0);
if (buf->bufused == 0)
max_read = 0;
else if ((buf->outptr - buf->inptr) >= 0)
max_read = buf->buflen - (buf->outptr - buf->buffer);
else
max_read = buf->inptr - buf->outptr;
return max_read;
}
gboolean purple_circ_buffer_mark_read(PurpleCircBuffer *buf, gsize len) {
g_return_val_if_fail(buf != NULL, FALSE);
g_return_val_if_fail(purple_circ_buffer_get_max_read(buf) >= len, FALSE);
buf->outptr += len;
buf->bufused -= len;
/* wrap to the start if we're at the end */
if ((gsize)(buf->outptr - buf->buffer) == buf->buflen)
buf->outptr = buf->buffer;
return TRUE;
}