Re: [PATCH 02/28] glib-compat: Introduce g_memdup2() wrapper

[Daniel P . Berrangé]

On Fri, Sep 03, 2021 at 01:06:36PM +0200, Philippe Mathieu-Daudé wrote:
> When experimenting raising GLIB_VERSION_MIN_REQUIRED to 2.68
> (Fedora 34 provides GLib 2.68.1) we get:
> 
>   hw/virtio/virtio-crypto.c:245:24: error: 'g_memdup' is deprecated: Use 
> 'g_memdup2' instead [-Werror,-Wdeprecated-declarations]
>   ...
> 
> g_memdup() has been updated by g_memdup2() to fix eventual security
> issues (size argument is 32-bit and could be truncated / wrapping).
> GLib recommends to copy their static inline version of g_memdup2():
> https://discourse.gnome.org/t/port-your-module-from-g-memdup-to-g-memdup2-now/5538
> 
> Our glib-compat.h provides a comment explaining how to deal with
> these deprecated declarations (see commit e71e8cc0355
> "glib: enforce the minimum required version and warn about old APIs").
> 
> Following this comment suggestion, implement the g_memdup2_qemu()
> wrapper to g_memdup2(), and use the safer equivalent inlined when
> we are using pre-2.68 GLib.
> 
> Reported-by: Eric Blake <eblake@redhat.com>
> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> ---
>  include/glib-compat.h | 36 ++++++++++++++++++++++++++++++++++++
>  1 file changed, 36 insertions(+)
> 
> diff --git a/include/glib-compat.h b/include/glib-compat.h
> index 9e95c888f54..6577d9ab393 100644
> --- a/include/glib-compat.h
> +++ b/include/glib-compat.h
> @@ -68,6 +68,42 @@
>   * without generating warnings.
>   */
>  
> +/*
> + * g_memdup2_qemu:
> + * @mem: (nullable): the memory to copy.
> + * @byte_size: the number of bytes to copy.
> + *
> + * Allocates @byte_size bytes of memory, and copies @byte_size bytes into it
> + * from @mem. If @mem is %NULL it returns %NULL.
> + *
> + * This replaces g_memdup(), which was prone to integer overflows when
> + * converting the argument from a #gsize to a #guint.
> + *
> + * This static inline version is a backport of the new public API from
> + * GLib 2.68, kept internal to GLib for backport to older stable releases.
> + * See https://gitlab.gnome.org/GNOME/glib/-/issues/2319.
> + *
> + * Returns: (nullable): a pointer to the newly-allocated copy of the memory,
> + *          or %NULL if @mem is %NULL.
> + */
> +static inline gpointer g_memdup2_qemu(gconstpointer mem, gsize byte_size)
> +{
> +#if GLIB_CHECK_VERSION(2, 68, 0)
> +    return g_memdup2(mem, byte_size);
> +#else
> +    gpointer new_mem;
> +
> +    if (mem && byte_size != 0) {
> +        new_mem = g_malloc(byte_size);
> +        memcpy(new_mem, mem, byte_size);
> +    } else {
> +        new_mem = NULL;
> +    }
> +
> +    return new_mem;
> +#endif
> +}

Close, but you missed the final piece of the puzzle

   #define g_memdup2(a) g_memdup2_qemu(a)


Such that in all following patches you can use the normal "g_memdup2"
API. This means when we later update min glib, we just delete the
compat code here, and the callers don't need updates.

Regards,
Daniel
-- 
|: https://berrange.com      -o-    https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org         -o-            https://fstop138.berrange.com :|
|: https://entangle-photo.org    -o-    https://www.instagram.com/dberrange :|