rst-malloc: Do not grow sh-remap memory

The mremap() grow on anonymous shared memory doesn't produce
usable segment, as the underlying kernel tmpfs file doesn't
get truncated. So any access to new mem will result in sigbus.

Disable this grow for now, we only need few of such memory.
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>
Reviewed-by: Cyrill Gorcunov <gorcunov@openvz.org>

criu/rst-malloc.c

@@ -66,7 +66,18 @@ static int grow_remap(struct rst_mem_type_s *t, int flag, unsigned long size)
 		 */
 		aux = mmap(NULL, size, PROT_READ | PROT_WRITE,
 				flag | MAP_ANON, 0, 0);
-	else
+	else {
+		if (flag & MAP_SHARED) {
+			/*
+			 * Anon shared memory cannot grow with
+			 * mremap, anon-shmem file size doesn't
+			 * chage and memory access generates
+			 * SIGBUS. We should truncate the guy,
+			 * but for now we don't need it.
+			 */
+			pr_err("Can't grow RM_SHREMAP memory\n");
+			return -1;
+		}
 		/*
 		 * We'll have to remap all objects into restorer
 		 * address space and get their new addresses. Since
@@ -78,6 +89,7 @@ static int grow_remap(struct rst_mem_type_s *t, int flag, unsigned long size)
 		 */
 		aux = mremap(t->buf, t->size,
 				t->size + size, MREMAP_MAYMOVE);
+	}
 	if (aux == MAP_FAILED)
 		return -1;