linux-kernel - [PATCH 5.3 054/193] ceph: dont try to handle hashed dentries in non-O_CREAT atomic

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Date:   Mon, 11 Nov 2019 19:27:16 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>,
        Jeff Layton <jlayton@...nel.org>,
        Ilya Dryomov <idryomov@...il.com>
Subject: [PATCH 5.3 054/193] ceph: dont try to handle hashed dentries in non-O_CREAT atomic_open

From: Jeff Layton <jlayton@...nel.org>

commit 5bb5e6ee6f5c557dcd19822eccd7bcced1e1a410 upstream.

If ceph_atomic_open is handed a !d_in_lookup dentry, then that means
that it already passed d_revalidate so we *know* that it's negative (or
at least was very recently). Just return -ENOENT in that case.

This also addresses a subtle bug in dentry handling. Non-O_CREAT opens
call atomic_open with the parent's i_rwsem shared, but calling
d_splice_alias on a hashed dentry requires the exclusive lock.

If ceph_atomic_open receives a hashed, negative dentry on a non-O_CREAT
open, and another client were to race in and create the file before we
issue our OPEN, ceph_fill_trace could end up calling d_splice_alias on
the dentry with the new inode with insufficient locks.

Cc: stable@...r.kernel.org
Reported-by: Al Viro <viro@...iv.linux.org.uk>
Signed-off-by: Jeff Layton <jlayton@...nel.org>
Signed-off-by: Ilya Dryomov <idryomov@...il.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/ceph/file.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/fs/ceph/file.c
+++ b/fs/ceph/file.c
@@ -458,6 +458,9 @@ int ceph_atomic_open(struct inode *dir,
 		err = ceph_security_init_secctx(dentry, mode, &as_ctx);
 		if (err < 0)
 			goto out_ctx;
+	} else if (!d_in_lookup(dentry)) {
+		/* If it's not being looked up, it's negative */
+		return -ENOENT;
 	}

 	/* do the open */