[PATCH] btrfs: fix potential null pointer dereference bug

[Cong Ding]

The bug happens when rb_node == NULL. It causes variable node to be NULL and
then the NULL pointer is dereferenced this line:
        BUG_ON((struct btrfs_root *)node->data != root);

So we check node before the dereference.

Signed-off-by: Cong Ding <dinggnu@xxxxxxxxx>
---
 fs/btrfs/relocation.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index 17c306b..938b037 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -1269,7 +1269,7 @@ static int __update_reloc_root(struct btrfs_root *root, int del)
 	}
 	spin_unlock(&rc->reloc_root_tree.lock);
 
-	BUG_ON((struct btrfs_root *)node->data != root);
+	BUG_ON(!node || (struct btrfs_root *)node->data != root);
 
 	if (!del) {
 		spin_lock(&rc->reloc_root_tree.lock);
-- 
1.7.10.4

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