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FFmpeg/libavformat/rtmpdh.c
Frank Plowman 42982b5a5d avformat/ffrtmpcrypt: Fix int-conversion warning 
The gcrypt definition of `bn_new` used to use the return statement
on errors, with an AVERROR return value, regardless of the signature
of the function where the macro is used - it is called in
`dh_generate_key` and `ff_dh_init` which return pointers. As a result,
compiling with gcrypt and the ffrtmpcrypt protocol resulted in an
int-conversion warning. GCC 14 may upgrade these to errors [1].

This patch fixes the problem by changing the macro to remove `AVERROR`
and instead set `bn` to null if the allocation fails. This is the
behaviour of all the other `bn_new` implementations and so the result is
already checked at all the callsites. AFAICT, this should be the only
change needed to get ffmpeg off Fedora's naughty list of projects with
warnings which may be upgraded to errors in GCC 14 [2].

[1]: https://gcc.gnu.org/pipermail/gcc/2023-May/241264.html
[2]: https://www.mail-archive.com/devel@lists.fedoraproject.org/msg196024.html

Signed-off-by: Frank Plowman <post@frankplowman.com>
Signed-off-by: Martin Storsjö <martin@martin.st>
2024-01-04 14:44:11 +02:00

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/*
* RTMP Diffie-Hellmann utilities
* Copyright (c) 2009 Andrej Stepanchuk
* Copyright (c) 2009-2010 Howard Chu
* Copyright (c) 2012 Samuel Pitoiset
*
* This file is part of FFmpeg.
*
* FFmpeg is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* FFmpeg 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
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with FFmpeg; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
/**
* @file
* RTMP Diffie-Hellmann utilities
*/
#include <stdint.h>
#include <string.h>
#include "config.h"
#include "libavutil/attributes.h"
#include "libavutil/error.h"
#include "libavutil/mem.h"
#include "libavutil/random_seed.h"
#include "rtmpdh.h"
#if CONFIG_MBEDTLS
#include <mbedtls/ctr_drbg.h>
#include <mbedtls/entropy.h>
#endif
#define P1024 \
"FFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD1" \
"29024E088A67CC74020BBEA63B139B22514A08798E3404DD" \
"EF9519B3CD3A431B302B0A6DF25F14374FE1356D6D51C245" \
"E485B576625E7EC6F44C42E9A637ED6B0BFF5CB6F406B7ED" \
"EE386BFB5A899FA5AE9F24117C4B1FE649286651ECE65381" \
"FFFFFFFFFFFFFFFF"
#define Q1024 \
"7FFFFFFFFFFFFFFFE487ED5110B4611A62633145C06E0E68" \
"948127044533E63A0105DF531D89CD9128A5043CC71A026E" \
"F7CA8CD9E69D218D98158536F92F8A1BA7F09AB6B6A8E122" \
"F242DABB312F3F637A262174D31BF6B585FFAE5B7A035BF6" \
"F71C35FDAD44CFD2D74F9208BE258FF324943328F67329C0" \
"FFFFFFFFFFFFFFFF"
#if CONFIG_GMP
#define bn_new(bn) \
do { \
bn = av_malloc(sizeof(*bn)); \
if (bn) \
mpz_init2(bn, 1); \
} while (0)
#define bn_free(bn) \
do { \
mpz_clear(bn); \
av_free(bn); \
} while (0)
#define bn_set_word(bn, w) mpz_set_ui(bn, w)
#define bn_cmp(a, b) mpz_cmp(a, b)
#define bn_copy(to, from) mpz_set(to, from)
#define bn_sub_word(bn, w) mpz_sub_ui(bn, bn, w)
#define bn_cmp_1(bn) mpz_cmp_ui(bn, 1)
#define bn_num_bytes(bn) (mpz_sizeinbase(bn, 2) + 7) / 8
#define bn_bn2bin(bn, buf, len) \
do { \
memset(buf, 0, len); \
if (bn_num_bytes(bn) <= len) \
mpz_export(buf, NULL, 1, 1, 0, 0, bn); \
} while (0)
#define bn_bin2bn(bn, buf, len) \
do { \
bn_new(bn); \
if (bn) \
mpz_import(bn, len, 1, 1, 0, 0, buf); \
} while (0)
#define bn_hex2bn(bn, buf, ret) \
do { \
bn_new(bn); \
if (bn) \
ret = (mpz_set_str(bn, buf, 16) == 0); \
else \
ret = 1; \
} while (0)
#define bn_random(bn, num_bits) \
do { \
int bits = num_bits; \
mpz_set_ui(bn, 0); \
for (bits = num_bits; bits > 0; bits -= 32) { \
mpz_mul_2exp(bn, bn, 32); \
mpz_add_ui(bn, bn, av_get_random_seed()); \
} \
mpz_fdiv_r_2exp(bn, bn, num_bits); \
} while (0)
static int bn_modexp(FFBigNum bn, FFBigNum y, FFBigNum q, FFBigNum p)
{
mpz_powm(bn, y, q, p);
return 0;
}
#elif CONFIG_GCRYPT
#define bn_new(bn) \
do { \
if (!gcry_control(GCRYCTL_INITIALIZATION_FINISHED_P)) { \
if (gcry_check_version("1.5.4")) { \
gcry_control(GCRYCTL_DISABLE_SECMEM, 0); \
gcry_control(GCRYCTL_INITIALIZATION_FINISHED, 0); \
} \
} \
if (gcry_control(GCRYCTL_INITIALIZATION_FINISHED_P)) \
bn = gcry_mpi_new(1); \
else \
bn = NULL; \
} while (0)
#define bn_free(bn) gcry_mpi_release(bn)
#define bn_set_word(bn, w) gcry_mpi_set_ui(bn, w)
#define bn_cmp(a, b) gcry_mpi_cmp(a, b)
#define bn_copy(to, from) gcry_mpi_set(to, from)
#define bn_sub_word(bn, w) gcry_mpi_sub_ui(bn, bn, w)
#define bn_cmp_1(bn) gcry_mpi_cmp_ui(bn, 1)
#define bn_num_bytes(bn) (gcry_mpi_get_nbits(bn) + 7) / 8
#define bn_bn2bin(bn, buf, len) gcry_mpi_print(GCRYMPI_FMT_USG, buf, len, NULL, bn)
#define bn_bin2bn(bn, buf, len) gcry_mpi_scan(&bn, GCRYMPI_FMT_USG, buf, len, NULL)
#define bn_hex2bn(bn, buf, ret) ret = (gcry_mpi_scan(&bn, GCRYMPI_FMT_HEX, buf, 0, 0) == 0)
#define bn_random(bn, num_bits) gcry_mpi_randomize(bn, num_bits, GCRY_WEAK_RANDOM)
static int bn_modexp(FFBigNum bn, FFBigNum y, FFBigNum q, FFBigNum p)
{
gcry_mpi_powm(bn, y, q, p);
return 0;
}
#elif CONFIG_OPENSSL
#define bn_new(bn) bn = BN_new()
#define bn_free(bn) BN_free(bn)
#define bn_set_word(bn, w) BN_set_word(bn, w)
#define bn_cmp(a, b) BN_cmp(a, b)
#define bn_copy(to, from) BN_copy(to, from)
#define bn_sub_word(bn, w) BN_sub_word(bn, w)
#define bn_cmp_1(bn) BN_cmp(bn, BN_value_one())
#define bn_num_bytes(bn) BN_num_bytes(bn)
#define bn_bn2bin(bn, buf, len) BN_bn2bin(bn, buf)
#define bn_bin2bn(bn, buf, len) bn = BN_bin2bn(buf, len, 0)
#define bn_hex2bn(bn, buf, ret) ret = BN_hex2bn(&bn, buf)
#define bn_random(bn, num_bits) BN_rand(bn, num_bits, 0, 0)
static int bn_modexp(FFBigNum bn, FFBigNum y, FFBigNum q, FFBigNum p)
{
BN_CTX *ctx = BN_CTX_new();
if (!ctx)
return AVERROR(ENOMEM);
if (!BN_mod_exp(bn, y, q, p, ctx)) {
BN_CTX_free(ctx);
return AVERROR(EINVAL);
}
BN_CTX_free(ctx);
return 0;
}
#elif CONFIG_MBEDTLS
#define bn_new(bn) \
do { \
bn = av_malloc(sizeof(*bn)); \
if (bn) \
mbedtls_mpi_init(bn); \
} while (0)
#define bn_free(bn) \
do { \
mbedtls_mpi_free(bn); \
av_free(bn); \
} while (0)
#define bn_set_word(bn, w) mbedtls_mpi_lset(bn, w)
#define bn_cmp(a, b) mbedtls_mpi_cmp_mpi(a, b)
#define bn_copy(to, from) mbedtls_mpi_copy(to, from)
#define bn_sub_word(bn, w) mbedtls_mpi_sub_int(bn, bn, w)
#define bn_cmp_1(bn) mbedtls_mpi_cmp_int(bn, 1)
#define bn_num_bytes(bn) (mbedtls_mpi_bitlen(bn) + 7) / 8
#define bn_bn2bin(bn, buf, len) mbedtls_mpi_write_binary(bn, buf, len)
#define bn_bin2bn(bn, buf, len) \
do { \
bn_new(bn); \
if (bn) \
mbedtls_mpi_read_binary(bn, buf, len); \
} while (0)
#define bn_hex2bn(bn, buf, ret) \
do { \
bn_new(bn); \
if (bn) \
ret = (mbedtls_mpi_read_string(bn, 16, buf) == 0); \
else \
ret = 1; \
} while (0)
#define bn_random(bn, num_bits) \
do { \
mbedtls_entropy_context entropy_ctx; \
mbedtls_ctr_drbg_context ctr_drbg_ctx; \
\
mbedtls_entropy_init(&entropy_ctx); \
mbedtls_ctr_drbg_init(&ctr_drbg_ctx); \
mbedtls_ctr_drbg_seed(&ctr_drbg_ctx, \
mbedtls_entropy_func, \
&entropy_ctx, \
NULL, 0); \
mbedtls_mpi_fill_random(bn, (num_bits + 7) / 8, mbedtls_ctr_drbg_random, &ctr_drbg_ctx); \
mbedtls_ctr_drbg_free(&ctr_drbg_ctx); \
mbedtls_entropy_free(&entropy_ctx); \
} while (0)
#define bn_modexp(bn, y, q, p) mbedtls_mpi_exp_mod(bn, y, q, p, 0)
#endif
#define MAX_BYTES 18000
#define dh_new() av_mallocz(sizeof(FF_DH))
static FFBigNum dh_generate_key(FF_DH *dh)
{
int num_bytes;
num_bytes = bn_num_bytes(dh->p) - 1;
if (num_bytes <= 0 || num_bytes > MAX_BYTES)
return NULL;
bn_new(dh->priv_key);
if (!dh->priv_key)
return NULL;
bn_random(dh->priv_key, 8 * num_bytes);
bn_new(dh->pub_key);
if (!dh->pub_key) {
bn_free(dh->priv_key);
return NULL;
}
if (bn_modexp(dh->pub_key, dh->g, dh->priv_key, dh->p) < 0)
return NULL;
return dh->pub_key;
}
static int dh_compute_key(FF_DH *dh, FFBigNum pub_key_bn,
uint32_t secret_key_len, uint8_t *secret_key)
{
FFBigNum k;
int ret;
bn_new(k);
if (!k)
return -1;
if ((ret = bn_modexp(k, pub_key_bn, dh->priv_key, dh->p)) < 0) {
bn_free(k);
return ret;
}
bn_bn2bin(k, secret_key, secret_key_len);
bn_free(k);
/* return the length of the shared secret key like DH_compute_key */
return secret_key_len;
}
void ff_dh_free(FF_DH *dh)
{
if (!dh)
return;
bn_free(dh->p);
bn_free(dh->g);
bn_free(dh->pub_key);
bn_free(dh->priv_key);
av_free(dh);
}
static int dh_is_valid_public_key(FFBigNum y, FFBigNum p, FFBigNum q)
{
FFBigNum bn = NULL;
int ret = AVERROR(EINVAL);
bn_new(bn);
if (!bn)
return AVERROR(ENOMEM);
/* y must lie in [2, p - 1] */
bn_set_word(bn, 1);
if (!bn_cmp(y, bn))
goto fail;
/* bn = p - 2 */
bn_copy(bn, p);
bn_sub_word(bn, 1);
if (!bn_cmp(y, bn))
goto fail;
/* Verify with Sophie-Germain prime
*
* This is a nice test to make sure the public key position is calculated
* correctly. This test will fail in about 50% of the cases if applied to
* random data.
*/
/* y must fulfill y^q mod p = 1 */
if ((ret = bn_modexp(bn, y, q, p)) < 0)
goto fail;
ret = AVERROR(EINVAL);
if (bn_cmp_1(bn))
goto fail;
ret = 0;
fail:
bn_free(bn);
return ret;
}
av_cold FF_DH *ff_dh_init(int key_len)
{
FF_DH *dh;
int ret;
if (!(dh = dh_new()))
return NULL;
bn_new(dh->g);
if (!dh->g)
goto fail;
bn_hex2bn(dh->p, P1024, ret);
if (!ret)
goto fail;
bn_set_word(dh->g, 2);
dh->length = key_len;
return dh;
fail:
ff_dh_free(dh);
return NULL;
}
int ff_dh_generate_public_key(FF_DH *dh)
{
int ret = 0;
while (!ret) {
FFBigNum q1 = NULL;
if (!dh_generate_key(dh))
return AVERROR(EINVAL);
bn_hex2bn(q1, Q1024, ret);
if (!ret)
return AVERROR(ENOMEM);
ret = dh_is_valid_public_key(dh->pub_key, dh->p, q1);
bn_free(q1);
if (!ret) {
/* the public key is valid */
break;
}
}
return ret;
}
int ff_dh_write_public_key(FF_DH *dh, uint8_t *pub_key, int pub_key_len)
{
int len;
/* compute the length of the public key */
len = bn_num_bytes(dh->pub_key);
if (len <= 0 || len > pub_key_len)
return AVERROR(EINVAL);
/* convert the public key value into big-endian form */
memset(pub_key, 0, pub_key_len);
bn_bn2bin(dh->pub_key, pub_key + pub_key_len - len, len);
return 0;
}
int ff_dh_compute_shared_secret_key(FF_DH *dh, const uint8_t *pub_key,
int pub_key_len, uint8_t *secret_key,
int secret_key_len)
{
FFBigNum q1 = NULL, pub_key_bn = NULL;
int ret;
/* convert the big-endian form of the public key into a bignum */
bn_bin2bn(pub_key_bn, pub_key, pub_key_len);
if (!pub_key_bn)
return AVERROR(ENOMEM);
/* convert the string containing a hexadecimal number into a bignum */
bn_hex2bn(q1, Q1024, ret);
if (!ret) {
ret = AVERROR(ENOMEM);
goto fail;
}
/* when the public key is valid we have to compute the shared secret key */
if ((ret = dh_is_valid_public_key(pub_key_bn, dh->p, q1)) < 0) {
goto fail;
} else if ((ret = dh_compute_key(dh, pub_key_bn, secret_key_len,
secret_key)) < 0) {
ret = AVERROR(EINVAL);
goto fail;
}
fail:
bn_free(pub_key_bn);
bn_free(q1);
return ret;
}
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