Re: [PATCH v3 1/2] migration/vmstate: Add VMState support for GByteArray

[Peter Xu <peterx@redhat.com>]

On Wed, Apr 22, 2026 at 01:52:13PM +0530, Arun Menon wrote:
> From: Arun Menon <armenon@redhat.com>
> 
> In GLib, GByteArray is an object managed by the library. Currently,
> migrating a GByteArray requires treating it as a raw C struct and using
> VMSTATE_VBUFFER_ALLOC_UINT32. For example, see vmstate_vdba in
> ui/vdagent.c
> 
> QEMU cannot pretend that GByteArray is a C struct and simply use
> VMS_ALLOC to g_malloc() the buffer. This is because, VMS_ALLOC blindly
> overwrites the data pointer with a newly allocated buffer, thereby
> leaking the previous memory. Besides, GLib tracks the array's capacity
> in a hidden alloc field. Bypassing GLib APIs leave this capacity out of
> sync with the newly allocated buffer, potentially leading to heap buffer
> overflows during subsequent g_byte_array_append() calls.
> 
> This commit introduces VMSTATE_GBYTEARRAY which uses specific library
> API calls (g_byte_array_set_size()) to safely resize and populate the
> buffer.
> 
> Signed-off-by: Arun Menon <armenon@redhat.com>
> Fix-Suggested-by: Marc-André Lureau <marcandre.lureau@redhat.com>

I think the common one is Suggested-by for this tag.

> Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>

Reviewed-by: Peter Xu <peterx@redhat.com>

Nitpicks only inline.

> ---
>  include/migration/vmstate.h | 10 ++++++++++
>  migration/vmstate-types.c   | 37 +++++++++++++++++++++++++++++++++++++
>  2 files changed, 47 insertions(+)
> 
> diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h
> index 62c2abd0c4..f503a40ec0 100644
> --- a/include/migration/vmstate.h
> +++ b/include/migration/vmstate.h
> @@ -265,6 +265,7 @@ extern const VMStateInfo vmstate_info_bitmap;
>  extern const VMStateInfo vmstate_info_qtailq;
>  extern const VMStateInfo vmstate_info_gtree;
>  extern const VMStateInfo vmstate_info_qlist;
> +extern const VMStateInfo vmstate_info_g_byte_array;
>  
>  #define type_check_2darray(t1,t2,n,m) ((t1(*)[n][m])0 - (t2*)0)
>  /*
> @@ -892,6 +893,15 @@ extern const VMStateInfo vmstate_info_qlist;
>      .start        = offsetof(_type, _next),                              \
>  }
>  
> +#define VMSTATE_GBYTEARRAY(_field, _state, _version) {                   \
> +    .name         = (stringify(_field)),                                 \
> +    .version_id   = (_version),                                          \
> +    .size         = sizeof(GByteArray),                                  \
> +    .info         = &vmstate_info_g_byte_array,                          \
> +    .flags        = VMS_SINGLE,                                          \
> +    .offset       = vmstate_offset_pointer(_state, _field, GByteArray),  \
> +}
> +
>  /* _f : field name
>     _f_n : num of elements field_name
>     _n : num of elements
> diff --git a/migration/vmstate-types.c b/migration/vmstate-types.c
> index 89cb211472..e3a47e60b1 100644
> --- a/migration/vmstate-types.c
> +++ b/migration/vmstate-types.c
> @@ -942,3 +942,40 @@ const VMStateInfo vmstate_info_qlist = {
>      .get  = get_qlist,
>      .put  = put_qlist,
>  };
> +
> +static int get_g_byte_array(QEMUFile *f, void *pv, size_t size,
> +                            const VMStateField *field)
> +{
> +    GByteArray **byte_array = (GByteArray **)pv;
> +    uint32_t len = qemu_get_be32(f);
> +
> +    assert(*byte_array != NULL);

We can make byte_array to be GByteArray* directly, it'll be the same as
assertion when deref NULL.

> +
> +    g_byte_array_set_size(*byte_array, len);
> +    if (len > 0) {
> +        qemu_get_buffer(f, (*byte_array)->data, len);
> +    }
> +    return 0;
> +}
> +
> +static int put_g_byte_array(QEMUFile *f, void *pv, size_t size,
> +                            const VMStateField *field, JSONWriter *vmdesc)
> +{
> +    GByteArray *byte_array = *(GByteArray **)pv;
> +    uint32_t len;
> +    assert(byte_array != NULL);
> +
> +    len = byte_array ? byte_array->len : 0;

This check is redundant.

> +    qemu_put_be32(f, len);
> +    if (len > 0) {
> +        qemu_put_buffer(f, byte_array->data, len);
> +    }
> +
> +    return 0;
> +}
> +
> +const VMStateInfo vmstate_info_g_byte_array = {
> +    .name = "GByteArray",
> +    .get  = get_g_byte_array,
> +    .put  = put_g_byte_array,
> +};
> -- 
> 2.53.0
> 

-- 
Peter Xu