block/export: Fix null pointer dereference in error path

There are some error paths in blk_exp_add() that jump to 'fail:' before
'exp' is even created. So we can't just unconditionally access exp->blk.

Add a NULL check, and switch from exp->blk to blk, which is available
earlier, just to be extra sure that we really cover all cases where
BlockDevOps could have been set for it (in practice, this only happens
in drv->create() today, so this part of the change isn't strictly
necessary).

Fixes: Coverity CID 1509238
Fixes: de79b52604e43fdeba6cee4f5af600b62169f2d2
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20230510203601.418015-3-kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Tested-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
(cherry picked from commit a184563778f2b8970eb93291f08108e66432a575)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

diff --git a/block/export/export.c b/block/export/export.c
index cdef2989027d3fa7db4a35ff7b32f74bccb3be1b..33f8f8ffa4364e87ef8e94a7682c8758fd978652 100644 (file)
--- a/block/export/export.c
+++ b/block/export/export.c
@@ -192,8 +192,10 @@ BlockExport *blk_exp_add(BlockExportOptions *export, Error **errp)
     return exp;
 
 fail:
-    blk_set_dev_ops(exp->blk, NULL, NULL);
-    blk_unref(blk);
+    if (blk) {
+        blk_set_dev_ops(blk, NULL, NULL);
+        blk_unref(blk);
+    }
     aio_context_release(ctx);
     if (exp) {
         g_free(exp->id);