block: Fix direct use of protocols as driver for bdrv_open()

bdrv_open_common() implements direct use of protocols by copying the
pre-opened BlockDriverStates to bs using bdrv_swap(). It did however
first set some fields in bs, which end up in file after the swap. When
bdrv_open() destroys file, it appears to be open, and because it isn't,
qemu could segfault while trying to close it.

Reorder the operations to return immediately in such cases so that file
is correctly detected as closed.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

diff --git a/block.c b/block.c
index 16a92a4e088b266655d0763e7c6fa1ccc6315f54..0ae2e93982f6dcc3cd94e7e56eefb901227891ec 100644 (file)
--- a/block.c
+++ b/block.c
@@ -680,6 +680,18 @@ static int bdrv_open_common(BlockDriverState *bs, BlockDriverState *file,
 
     trace_bdrv_open_common(bs, filename, flags, drv->format_name);
 
+    if (use_bdrv_whitelist && !bdrv_is_whitelisted(drv)) {
+        return -ENOTSUP;
+    }
+
+    /* bdrv_open() with directly using a protocol as drv. This layer is already
+     * opened, so assign it to bs (while file becomes a closed BlockDriverState)
+     * and return immediately. */
+    if (file != NULL && drv->bdrv_file_open) {
+        bdrv_swap(file, bs);
+        return 0;
+    }
+
     bs->open_flags = flags;
     bs->buffer_alignment = 512;
 
@@ -694,10 +706,6 @@ static int bdrv_open_common(BlockDriverState *bs, BlockDriverState *file,
         bs->filename[0] = '\0';
     }
 
-    if (use_bdrv_whitelist && !bdrv_is_whitelisted(drv)) {
-        return -ENOTSUP;
-    }
-
     bs->drv = drv;
     bs->opaque = g_malloc0(drv->instance_size);
 
@@ -708,13 +716,9 @@ static int bdrv_open_common(BlockDriverState *bs, BlockDriverState *file,
 
     /* Open the image, either directly or using a protocol */
     if (drv->bdrv_file_open) {
-        if (file != NULL) {
-            bdrv_swap(file, bs);
-            ret = 0;
-        } else {
-            assert(drv->bdrv_parse_filename || filename != NULL);
-            ret = drv->bdrv_file_open(bs, filename, options, open_flags);
-        }
+        assert(file == NULL);
+        assert(drv->bdrv_parse_filename || filename != NULL);
+        ret = drv->bdrv_file_open(bs, filename, options, open_flags);
     } else {
         assert(file != NULL);
         bs->file = file;