[PATCH] fs: Detect API misuse of i_op->lookup

[Richard Weinberger]

Hunting down a refcount issue in an out-of-tree filesystem uncovered
that its lookup function directly returned the dentry which was passed to it.
Add a BUG_ON() to detect such misuse in future.

Signed-off-by: Richard Weinberger <richard@xxxxxx>
---
 fs/namei.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/namei.c b/fs/namei.c
index bc35b02..f8ccae6 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1370,6 +1370,7 @@ static struct dentry *lookup_real(struct inode *dir, struct dentry *dentry,
 
 	old = dir->i_op->lookup(dir, dentry, flags);
 	if (unlikely(old)) {
+		BUG_ON(old == dentry);
 		dput(dentry);
 		dentry = old;
 	}
-- 
2.2.2

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