3.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Andreas Dilger <redacted>

commit 7e936b737211e6b54e34b71a827e56b872e958d8 upstream.

A hard-linked directory to its parent can cause the VFS to deadlock,
and is a sign of a corrupted file system.  So detect this case in
ext4_lookup(), before the rmdir() lockup scenario can take place.

Signed-off-by: Andreas Dilger <redacted>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Ben Hutchings <redacted>
---
 fs/ext4/namei.c |    6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index a9fd5f4..daf8260 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c

@@ -1330,6 +1330,12 @@ static struct dentry *ext4_lookup(struct inode *dir, struct dentry *dentry, stru
 			EXT4_ERROR_INODE(dir, "bad inode number: %u", ino);
 			return ERR_PTR(-EIO);
 		}
+		if (unlikely(ino == dir->i_ino)) {
+			EXT4_ERROR_INODE(dir, "'%.*s' linked to parent dir",
+					 dentry->d_name.len,
+					 dentry->d_name.name);
+			return ERR_PTR(-EIO);
+		}
 		inode = ext4_iget(dir->i_sb, ino);
 		if (inode == ERR_PTR(-ESTALE)) {
 			EXT4_ERROR_INODE(dir,