[PATCH 1/3] ui/spice-display: Avoid dynamic stack allocation

[Peter Maydell]

Use an autofree heap allocation instead of a variable-length
array on the stack in qemu_spice_create_update().

The codebase has very few VLAs, and if we can get rid of them all we
can make the compiler error on new additions.  This is a defensive
measure against security bugs where an on-stack dynamic allocation
isn't correctly size-checked (e.g.  CVE-2021-3527).

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
I was a little unsure about this allocation given that it's
in the display_refresh callback, but the code already does
a g_malloc() every time it calls qemu_spice_create_one_update()
so one more presumably won't hurt.
---
 ui/spice-display.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/ui/spice-display.c b/ui/spice-display.c
index 3f3f8013d86..0e2fbfb17c1 100644
--- a/ui/spice-display.c
+++ b/ui/spice-display.c
@@ -189,7 +189,7 @@ static void qemu_spice_create_update(SimpleSpiceDisplay 
*ssd)
 {
     static const int blksize = 32;
     int blocks = DIV_ROUND_UP(surface_width(ssd->ds), blksize);
-    int dirty_top[blocks];
+    g_autofree int *dirty_top = NULL;
     int y, yoff1, yoff2, x, xoff, blk, bw;
     int bpp = surface_bytes_per_pixel(ssd->ds);
     uint8_t *guest, *mirror;
@@ -198,6 +198,7 @@ static void qemu_spice_create_update(SimpleSpiceDisplay 
*ssd)
         return;
     };
 
+    dirty_top = g_new(int, blocks);
     for (blk = 0; blk < blocks; blk++) {
         dirty_top[blk] = -1;
     }
-- 
2.34.1