vnc_refresh_lossy_rect() marks a full VNC_STAT_RECT (64) rows of the dirty bitmap when refreshing a lossy tile. When the display height is not a multiple of VNC_STAT_RECT, the last tile row is a partial tile and the loop writes past the end of vs->dirty[VNC_MAX_HEIGHT].
For example, with a 2160-pixel-high display (VNC_MAX_HEIGHT), the last stat tile starts at y=2112. The unconditional 64-row loop writes rows 2112..2175, overflowing 16 rows (640 bytes) past the dirty bitmap into subsequent VncState fields. Fix by passing the effective display height into vnc_refresh_lossy_rect() and clamping the inner loop. Fixes: CVE-2026-61475 Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/3935 Reported-by: "Vulnerability Report" <[email protected]> Reviewed-by: Philippe Mathieu-Daudé <[email protected]> Signed-off-by: Marc-Andre Lureau <[email protected]> --- ui/vnc.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/ui/vnc.c b/ui/vnc.c index 8d91cee4d9f..c957731877f 100644 --- a/ui/vnc.c +++ b/ui/vnc.c @@ -3000,18 +3000,18 @@ void vnc_sent_lossy_rect(VncWorker *worker, int x, int y, int w, int h) } } -static int vnc_refresh_lossy_rect(VncDisplay *vd, int x, int y) +static int vnc_refresh_lossy_rect(VncDisplay *vd, int x, int y, + int height) { VncState *vs; int sty = y / VNC_STAT_RECT; int stx = x / VNC_STAT_RECT; int has_dirty = 0; - int height = MIN(pixman_image_get_height(vd->guest.fb), - pixman_image_get_height(vd->server)); int rows; y = QEMU_ALIGN_DOWN(y, VNC_STAT_RECT); x = QEMU_ALIGN_DOWN(x, VNC_STAT_RECT); + rows = MIN(VNC_STAT_RECT, height - y); rows = MIN(VNC_STAT_RECT, height - y); if (rows <= 0) { @@ -3083,7 +3083,7 @@ static int vnc_update_stats(VncDisplay *vd, struct timeval * tv) if (timercmp(&res, &VNC_REFRESH_LOSSY, >)) { rect->freq = 0; - has_dirty += vnc_refresh_lossy_rect(vd, x, y); + has_dirty += vnc_refresh_lossy_rect(vd, x, y, height); memset(rect->times, 0, sizeof (rect->times)); continue ; } -- 2.55.0
