linux-kernel - [PATCH 3.16 292/366] ufs: Fix possible deadlock when looking up directories

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Message-ID: <lsq.1539530741.361847216@decadent.org.uk>
Date:   Sun, 14 Oct 2018 16:25:41 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Jan Kara" <jack@...e.cz>,
        "Al Viro" <viro@...iv.linux.org.uk>,
        "Fabian Frederick" <fabf@...net.be>
Subject: [PATCH 3.16 292/366] ufs: Fix possible deadlock when looking up
 directories

3.16.60-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Jan Kara <jack@...e.cz>

commit 514d748f69c97a51a2645eb198ac5c6218f22ff9 upstream.

Commit e4502c63f56aeca88 (ufs: deal with nfsd/iget races) made ufs
create inodes with I_NEW flag set. However ufs_mkdir() never cleared
this flag. Thus if someone ever tried to lookup the directory by inode
number, he would deadlock waiting for I_NEW to be cleared. Luckily this
mostly happens only if the filesystem is exported over NFS since
otherwise we have the inode attached to dentry and don't look it up by
inode number. In rare cases dentry can get freed without inode being
freed and then we'd hit the deadlock even without NFS export.

Fix the problem by clearing I_NEW before instantiating new directory
inode.

Fixes: e4502c63f56aeca887ced37f24e0def1ef11cec8
Reported-by: Fabian Frederick <fabf@...net.be>
Signed-off-by: Jan Kara <jack@...e.cz>
Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 fs/ufs/namei.c | 1 +
 1 file changed, 1 insertion(+)

--- a/fs/ufs/namei.c
+++ b/fs/ufs/namei.c
@@ -212,6 +212,7 @@ static int ufs_mkdir(struct inode * dir,
 		goto out_fail;
 	unlock_ufs(dir->i_sb);

+	unlock_new_inode(inode);
 	d_instantiate(dentry, inode);
 out:
 	return err;