[PATCH v2] ui/cursor: make width/height unsigned 16-bit integer

[Mauro Matteo Cascella <mcascell@redhat.com>]

Although not actually exploitable at the moment, a negative width/height
could make datasize wrap around and potentially lead to buffer overflow.
Since there is no reason a negative width/height is ever appropriate,
modify QEMUCursor struct and cursor_alloc prototype to accept uint16_t.
This protects us against accidentally introducing future bugs.

Signed-off-by: Mauro Matteo Cascella <mcascell@redhat.com>
Reported-by: Jacek Halon <jacek.halon@gmail.com>
Reported-by: Yair Mizrahi <yairh33@gmail.com>
Reported-by: Elsayed El-Refa'ei <e.elrefaei99@gmail.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
---
v2:
- update commit summary/description
- add Reported-by/Reviewed-by
- use uint16_t instead of uint32_t
- add comment in cursor_alloc

 include/ui/console.h | 4 ++--
 ui/cursor.c          | 3 ++-
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/include/ui/console.h b/include/ui/console.h
index 2a8fab091f..ae5ec466c1 100644
--- a/include/ui/console.h
+++ b/include/ui/console.h
@@ -144,13 +144,13 @@ typedef struct QemuUIInfo {
 
 /* cursor data format is 32bit RGBA */
 typedef struct QEMUCursor {
-    int                 width, height;
+    uint16_t            width, height;
     int                 hot_x, hot_y;
     int                 refcount;
     uint32_t            data[];
 } QEMUCursor;
 
-QEMUCursor *cursor_alloc(int width, int height);
+QEMUCursor *cursor_alloc(uint16_t width, uint16_t height);
 QEMUCursor *cursor_ref(QEMUCursor *c);
 void cursor_unref(QEMUCursor *c);
 QEMUCursor *cursor_builtin_hidden(void);
diff --git a/ui/cursor.c b/ui/cursor.c
index 6fe67990e2..29717b3ecb 100644
--- a/ui/cursor.c
+++ b/ui/cursor.c
@@ -90,11 +90,12 @@ QEMUCursor *cursor_builtin_left_ptr(void)
     return cursor_parse_xpm(cursor_left_ptr_xpm);
 }
 
-QEMUCursor *cursor_alloc(int width, int height)
+QEMUCursor *cursor_alloc(uint16_t width, uint16_t height)
 {
     QEMUCursor *c;
     size_t datasize = width * height * sizeof(uint32_t);
 
+    /* Modern physical hardware typically uses 512x512 sprites */
     if (width > 512 || height > 512) {
         return NULL;
     }
-- 
2.40.1