NetworkManager/shared/nm-glib-aux/nm-secret-utils.c

/* SPDX-License-Identifier: LGPL-2.1+ */
/*
 * Copyright (C) 2018 Red Hat, Inc.
 * Copyright (C) 2015 - 2019 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
 */

#include "nm-default.h"

#include "nm-secret-utils.h"

#include <malloc.h>

/*****************************************************************************/

void
nm_explicit_bzero(void *s, gsize n)
{
    /* gracefully handle n == 0. This is important, callers rely on it. */
    if (G_UNLIKELY(n == 0))
        return;

    nm_assert(s);

#if defined(HAVE_DECL_EXPLICIT_BZERO) && HAVE_DECL_EXPLICIT_BZERO
    explicit_bzero(s, n);
#else
    {
        volatile guint8 *p = s;

        memset(s, '\0', n);
        while (n-- > 0)
            *(p++) = '\0';
    }
#endif
}

void
nm_free_secret(char *secret)
{
    gsize len;

    if (!secret)
        return;

#if GLIB_CHECK_VERSION(2, 44, 0)
    /* Here we mix malloc() and g_malloc() API. Usually we avoid this,
     * however since glib 2.44.0 we are in fact guaranteed that g_malloc()/g_free()
     * just wraps malloc()/free(), so this is actually fine.
     *
     * See https://gitlab.gnome.org/GNOME/glib/commit/3be6ed60aa58095691bd697344765e715a327fc1
     */
    len = malloc_usable_size(secret);
#else
    len = strlen(secret);
#endif

    nm_explicit_bzero(secret, len);
    g_free(secret);
}

/*****************************************************************************/

char *
nm_secret_strchomp(char *secret)
{
    gsize len;

    g_return_val_if_fail(secret, NULL);

    /* it's actually identical to g_strchomp(). However,
     * the glib function does not document, that it clears the
     * memory. For @secret, we don't only want to truncate trailing
     * spaces, we want to overwrite them with NUL. */

    len = strlen(secret);
    while (len--) {
        if (g_ascii_isspace((guchar) secret[len]))
            secret[len] = '\0';
        else
            break;
    }

    return secret;
}

/*****************************************************************************/

GBytes *
nm_secret_copy_to_gbytes(gconstpointer mem, gsize mem_len)
{
    NMSecretBuf *b;

    if (mem_len == 0)
        return g_bytes_new_static("", 0);

    nm_assert(mem);

    /* NUL terminate the buffer.
     *
     * The entire buffer is already malloc'ed and likely has some room for padding.
     * Thus, in many situations, this additional byte will cause no overhead in
     * practice.
     *
     * Even if it causes an overhead, do it just for safety. Yes, the returned
     * bytes is not a NUL terminated string and no user must rely on this. Do
     * not treat binary data as NUL terminated strings, unless you know what
     * you are doing. Anyway, defensive FTW.
     */

    b = nm_secret_buf_new(mem_len + 1);
    memcpy(b->bin, mem, mem_len);
    b->bin[mem_len] = 0;
    return nm_secret_buf_to_gbytes_take(b, mem_len);
}

/*****************************************************************************/

NMSecretBuf *
nm_secret_buf_new(gsize len)
{
    NMSecretBuf *secret;

    nm_assert(len > 0);

    secret                      = g_malloc(sizeof(NMSecretBuf) + len);
    *((gsize *) &(secret->len)) = len;
    return secret;
}

static void
_secret_buf_free(gpointer user_data)
{
    NMSecretBuf *secret = user_data;

    nm_assert(secret);
    nm_assert(secret->len > 0);

    nm_explicit_bzero(secret->bin, secret->len);
    g_free(user_data);
}

GBytes *
nm_secret_buf_to_gbytes_take(NMSecretBuf *secret, gssize actual_len)
{
    nm_assert(secret);
    nm_assert(secret->len > 0);
    nm_assert(actual_len == -1 || (actual_len >= 0 && actual_len <= secret->len));
    return g_bytes_new_with_free_func(secret->bin,
                                      actual_len >= 0 ? (gsize) actual_len : secret->len,
                                      _secret_buf_free,
                                      secret);
}

/*****************************************************************************/

/**
 * nm_utils_memeqzero_secret:
 * @data: the data pointer to check (may be %NULL if @length is zero).
 * @length: the number of bytes to check.
 *
 * Checks that all bytes are zero. This always takes the same amount
 * of time to prevent timing attacks.
 *
 * Returns: whether all bytes are zero.
 */
gboolean
nm_utils_memeqzero_secret(gconstpointer data, gsize length)
{
    const guint8 *const key = data;
    volatile guint8     acc = 0;
    gsize               i;

    for (i = 0; i < length; i++) {
        acc |= key[i];
        asm volatile("" : "=r"(acc) : "0"(acc));
    }
    return 1 & ((acc - 1) >> 8);
}