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

[Vladimir Sementsov-Ogievskiy]

03.09.2021 14:16, Daniel P. Berrangé wrote:
> 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.

That was most probably already discussed, so sorry my question:

Why we can't just do

#if ! GLIB_CHECK_VERSION(2, 68, 0)
static inline gpointer g_memdup2(gconstpointer mem, gsize byte_size)
{
    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

?


--
Best regards,
Vladimir