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

[Philippe Mathieu-Daudé]

On 9/3/21 1:16 PM, 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)

Doh :/

> 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.

Painful rebase in perspective...