Re: [PATCH v3 02/28] glib-compat: Introduce g_memdup2() wrapper

[Daniel P . Berrangé]

On Fri, Dec 17, 2021 at 02:53:05PM +0000, Alex Bennée wrote:
> 
> Daniel P. Berrangé <berrange@redhat.com> writes:
> 
> > On Thu, Dec 16, 2021 at 02:11:37PM +0000, Alex Bennée wrote:
> >> 
> >> Philippe Mathieu-Daudé <philmd@redhat.com> writes:
> >> 
> >> > 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 | 37 +++++++++++++++++++++++++++++++++++++
> >> >  1 file changed, 37 insertions(+)
> >> >
> >> > diff --git a/include/glib-compat.h b/include/glib-compat.h
> >> > index 9e95c888f54..8d01a8c01fb 100644
> >> > --- a/include/glib-compat.h
> >> > +++ b/include/glib-compat.h
> >> > @@ -68,6 +68,43 @@
> >> >   * 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
> >> > +}
> >> > +#define g_memdup2(m, s) g_memdup2_qemu(m, s)
> >> > +
> >> 
> >> As per our style wouldn't it make sense to just call it qemu_memdup(m,
> >> s)?
> >
> > Not in this case. We use suffix as we don't want people calling this
> > directly with the suffix.
> >
> > In the glibcompat.h header we're attempting to transparently/secretly
> > replace/wrap standard glib APIs.  All the callers should remain using
> > the plain glib API name, never call the method with the suffix at
> > all. This lets us delete the wrapper later and not have to update
> > any callers. The suffix is basically just a hack of the impl we use
> > for transparent replacement.
> 
> Right - at the risk of bike shedding names maybe we should choose a
> suffix the better reflects the purpose like _alt or _internal rather
> than overloading qemu?

Sure, I'm fine with that.

Regards,
Daniel
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