memory: cleanup side effects of memory_region_init_foo() on failure

if MemoryRegion intialization fails it's left in semi-initialized state,
where it's size is not 0 and attached as child to owner object.
And this leds to crash in following use-case:
    (monitor) object_add memory-backend-file,id=mem1,size=99999G,mem-path=/tmp/foo,discard-data=yes
    memory.c:2083: memory_region_get_ram_ptr: Assertion `mr->ram_block' failed
    Aborted (core dumped)
it happens due to assumption that memory region is intialized when
   memory_region_size() != 0
and therefore it's ok to access it in
   file_backend_unparent()
      if (memory_region_size() != 0)
          memory_region_get_ram_ptr()

which happens when object_add fails and unparents failed backend making
file_backend_unparent() access invalid memory region.

Fix it by making sure that memory_region_init_foo() APIs cleanup externally
visible side effects on failure (like set size to 0 and unparenting object)

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Message-Id: <1536064777-42312-1-git-send-email-imammedo@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

memory.c

@@ -1518,12 +1518,18 @@ void memory_region_init_ram_shared_nomigrate(MemoryRegion *mr,
                                              bool share,
                                              Error **errp)
 {
+    Error *err = NULL;
     memory_region_init(mr, owner, name, size);
     mr->ram = true;
     mr->terminates = true;
     mr->destructor = memory_region_destructor_ram;
-    mr->ram_block = qemu_ram_alloc(size, share, mr, errp);
+    mr->ram_block = qemu_ram_alloc(size, share, mr, &err);
     mr->dirty_log_mask = tcg_enabled() ? (1 << DIRTY_MEMORY_CODE) : 0;
+    if (err) {
+        mr->size = int128_zero();
+        object_unparent(OBJECT(mr));
+        error_propagate(errp, err);
+    }
 }
 
 void memory_region_init_resizeable_ram(MemoryRegion *mr,
@@ -1536,13 +1542,19 @@ void memory_region_init_resizeable_ram(MemoryRegion *mr,
                                                        void *host),
                                        Error **errp)
 {
+    Error *err = NULL;
     memory_region_init(mr, owner, name, size);
     mr->ram = true;
     mr->terminates = true;
     mr->destructor = memory_region_destructor_ram;
     mr->ram_block = qemu_ram_alloc_resizeable(size, max_size, resized,
-                                              mr, errp);
+                                              mr, &err);
     mr->dirty_log_mask = tcg_enabled() ? (1 << DIRTY_MEMORY_CODE) : 0;
+    if (err) {
+        mr->size = int128_zero();
+        object_unparent(OBJECT(mr));
+        error_propagate(errp, err);
+    }
 }
 
 #ifdef __linux__
@@ -1555,13 +1567,19 @@ void memory_region_init_ram_from_file(MemoryRegion *mr,
                                       const char *path,
                                       Error **errp)
 {
+    Error *err = NULL;
     memory_region_init(mr, owner, name, size);
     mr->ram = true;
     mr->terminates = true;
     mr->destructor = memory_region_destructor_ram;
     mr->align = align;
-    mr->ram_block = qemu_ram_alloc_from_file(size, mr, ram_flags, path, errp);
+    mr->ram_block = qemu_ram_alloc_from_file(size, mr, ram_flags, path, &err);
     mr->dirty_log_mask = tcg_enabled() ? (1 << DIRTY_MEMORY_CODE) : 0;
+    if (err) {
+        mr->size = int128_zero();
+        object_unparent(OBJECT(mr));
+        error_propagate(errp, err);
+    }
 }
 
 void memory_region_init_ram_from_fd(MemoryRegion *mr,
@@ -1572,14 +1590,20 @@ void memory_region_init_ram_from_fd(MemoryRegion *mr,
                                     int fd,
                                     Error **errp)
 {
+    Error *err = NULL;
     memory_region_init(mr, owner, name, size);
     mr->ram = true;
     mr->terminates = true;
     mr->destructor = memory_region_destructor_ram;
     mr->ram_block = qemu_ram_alloc_from_fd(size, mr,
                                            share ? RAM_SHARED : 0,
-                                           fd, errp);
+                                           fd, &err);
     mr->dirty_log_mask = tcg_enabled() ? (1 << DIRTY_MEMORY_CODE) : 0;
+    if (err) {
+        mr->size = int128_zero();
+        object_unparent(OBJECT(mr));
+        error_propagate(errp, err);
+    }
 }
 #endif
 
@@ -1630,13 +1654,19 @@ void memory_region_init_rom_nomigrate(MemoryRegion *mr,
                                       uint64_t size,
                                       Error **errp)
 {
+    Error *err = NULL;
     memory_region_init(mr, owner, name, size);
     mr->ram = true;
     mr->readonly = true;
     mr->terminates = true;
     mr->destructor = memory_region_destructor_ram;
-    mr->ram_block = qemu_ram_alloc(size, false, mr, errp);
+    mr->ram_block = qemu_ram_alloc(size, false, mr, &err);
     mr->dirty_log_mask = tcg_enabled() ? (1 << DIRTY_MEMORY_CODE) : 0;
+    if (err) {
+        mr->size = int128_zero();
+        object_unparent(OBJECT(mr));
+        error_propagate(errp, err);
+    }
 }
 
 void memory_region_init_rom_device_nomigrate(MemoryRegion *mr,
@@ -1647,14 +1677,20 @@ void memory_region_init_rom_device_nomigrate(MemoryRegion *mr,
                                              uint64_t size,
                                              Error **errp)
 {
+    Error *err = NULL;
     assert(ops);
     memory_region_init(mr, owner, name, size);
     mr->ops = ops;
     mr->opaque = opaque;
     mr->terminates = true;
     mr->rom_device = true;
     mr->destructor = memory_region_destructor_ram;
-    mr->ram_block = qemu_ram_alloc(size, false,  mr, errp);
+    mr->ram_block = qemu_ram_alloc(size, false,  mr, &err);
+    if (err) {
+        mr->size = int128_zero();
+        object_unparent(OBJECT(mr));
+        error_propagate(errp, err);
+    }
 }
 
 void memory_region_init_iommu(void *_iommu_mr,