shm: Fix use-after-free in ShmDestroyPixmap

We pass the pPixmap->drawable.id to the ShmDetachSegment function after
the pPixmap is freed. Fortunately, we don't use the value inside
ShmDetachSegment and can simply pass zero instead.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Michel Dänzer <michel@daenzer.net>

1 files changed, 2 insertions, 2 deletions

diff --git a/Xext/shm.c b/Xext/shm.c
index db9d47450..52d997425 100644
--- a/Xext/shm.c
+++ b/Xext/shm.c
@@ -260,7 +260,7 @@ ShmDestroyPixmap(PixmapPtr pPixmap)
     pScreen->DestroyPixmap = ShmDestroyPixmap;
 
     if (shmdesc)
-	ShmDetachSegment(shmdesc, pPixmap->drawable.id);
+	ShmDetachSegment(shmdesc, 0);
 
     return ret;
 }
@@ -427,7 +427,7 @@ ProcShmAttach(ClientPtr client)
 
  /*ARGSUSED*/ static int
 ShmDetachSegment(void *value, /* must conform to DeleteType */
-                 XID shmseg)
+                 XID unused)
 {
     ShmDescPtr shmdesc = (ShmDescPtr) value;
     ShmDescPtr *prev;