Re: [PATCH v3] ui/cursor: fix integer overflow in cursor_alloc (CVE-2021-4206)

[Mauro Matteo Cascella]

On Thu, Apr 7, 2022 at 11:17 AM Marc-André Lureau
<marcandre.lureau@gmail.com> wrote:
>
>
>
> On Thu, Apr 7, 2022 at 12:23 PM Mauro Matteo Cascella <mcascell@redhat.com> 
> wrote:
>>
>> Prevent potential integer overflow by limiting 'width' and 'height' to
>> 512x512. Also change 'datasize' type to size_t. Refer to security
>> advisory https://starlabs.sg/advisories/22-4206/ for more information.
>>
>> Fixes: CVE-2021-4206
>
>
> (the Starlabs advisory has 2022, I guess it's wrong then)

Yep, that is wrong. I asked them to update the page.

Thanks.

>> Signed-off-by: Mauro Matteo Cascella <mcascell@redhat.com>
>
>
> Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
>
>
>>
>> ---
>> v3:
>> - fix CVE id (CVE-2021-4206 instead of CVE-2022-4206)
>>
>>  hw/display/qxl-render.c | 7 +++++++
>>  hw/display/vmware_vga.c | 2 ++
>>  ui/cursor.c             | 8 +++++++-
>>  3 files changed, 16 insertions(+), 1 deletion(-)
>>
>> diff --git a/hw/display/qxl-render.c b/hw/display/qxl-render.c
>> index d28849b121..dc3c4edd05 100644
>> --- a/hw/display/qxl-render.c
>> +++ b/hw/display/qxl-render.c
>> @@ -247,6 +247,13 @@ static QEMUCursor *qxl_cursor(PCIQXLDevice *qxl, 
>> QXLCursor *cursor,
>>      size_t size;
>>
>>      c = cursor_alloc(cursor->header.width, cursor->header.height);
>> +
>> +    if (!c) {
>> +        qxl_set_guest_bug(qxl, "%s: cursor %ux%u alloc error", __func__,
>> +                cursor->header.width, cursor->header.height);
>> +        goto fail;
>> +    }
>> +
>>      c->hot_x = cursor->header.hot_spot_x;
>>      c->hot_y = cursor->header.hot_spot_y;
>>      switch (cursor->header.type) {
>> diff --git a/hw/display/vmware_vga.c b/hw/display/vmware_vga.c
>> index 98c83474ad..45d06cbe25 100644
>> --- a/hw/display/vmware_vga.c
>> +++ b/hw/display/vmware_vga.c
>> @@ -515,6 +515,8 @@ static inline void vmsvga_cursor_define(struct 
>> vmsvga_state_s *s,
>>      int i, pixels;
>>
>>      qc = cursor_alloc(c->width, c->height);
>> +    assert(qc != NULL);
>> +
>>      qc->hot_x = c->hot_x;
>>      qc->hot_y = c->hot_y;
>>      switch (c->bpp) {
>> diff --git a/ui/cursor.c b/ui/cursor.c
>> index 1d62ddd4d0..835f0802f9 100644
>> --- a/ui/cursor.c
>> +++ b/ui/cursor.c
>> @@ -46,6 +46,8 @@ static QEMUCursor *cursor_parse_xpm(const char *xpm[])
>>
>>      /* parse pixel data */
>>      c = cursor_alloc(width, height);
>> +    assert(c != NULL);
>> +
>>      for (pixel = 0, y = 0; y < height; y++, line++) {
>>          for (x = 0; x < height; x++, pixel++) {
>>              idx = xpm[line][x];
>> @@ -91,7 +93,11 @@ QEMUCursor *cursor_builtin_left_ptr(void)
>>  QEMUCursor *cursor_alloc(int width, int height)
>>  {
>>      QEMUCursor *c;
>> -    int datasize = width * height * sizeof(uint32_t);
>> +    size_t datasize = width * height * sizeof(uint32_t);
>> +
>> +    if (width > 512 || height > 512) {
>> +        return NULL;
>> +    }
>>
>>      c = g_malloc0(sizeof(QEMUCursor) + datasize);
>>      c->width  = width;
>> --
>> 2.35.1
>>
>>
>
>
> --
> Marc-André Lureau



-- 
Mauro Matteo Cascella
Red Hat Product Security
PGP-Key ID: BB3410B0