linux-kernel - [PATCH v2] ceph: don't return -ESTALE if there's still an open file

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <20200518174726.GA84496@suse.com>
Date:   Mon, 18 May 2020 18:47:26 +0100
From:   Luis Henriques <lhenriques@...e.com>
To:     Jeff Layton <jlayton@...nel.org>,
        Amir Goldstein <amir73il@...il.com>,
        Ilya Dryomov <idryomov@...il.com>
Cc:     ceph-devel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2] ceph: don't return -ESTALE if there's still an open file

Similarly to commit 03f219041fdb ("ceph: check i_nlink while converting
a file handle to dentry"), this fixes another corner case with
name_to_handle_at/open_by_handle_at.  The issue has been detected by
xfstest generic/467, when doing:

 - name_to_handle_at("/cephfs/myfile")
 - open("/cephfs/myfile")
 - unlink("/cephfs/myfile")
 - sync; sync;
 - drop caches
 - open_by_handle_at()

The call to open_by_handle_at should not fail because the file hasn't been
deleted yet (only unlinked) and we do have a valid handle to it.  -ESTALE
shall be returned only if i_nlink is 0 *and* i_count is 1.

This patch also makes sure we have LINK caps before checking i_nlink.

Signed-off-by: Luis Henriques <lhenriques@...e.com>
---
Hi!

(and sorry for the delay in my reply!)

So, from the discussion thread and some IRC chat with Jeff, I'm sending
v2.  What changed?  Everything! :-)

- Use i_count instead of __ceph_is_file_opened to check for open files
- Add call to ceph_do_getattr to make sure we have LINK caps before
  accessing i_nlink

Cheers,
--
Luis

 fs/ceph/export.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/fs/ceph/export.c b/fs/ceph/export.c
index 79dc06881e78..e088843a7734 100644
--- a/fs/ceph/export.c
+++ b/fs/ceph/export.c
@@ -172,9 +172,16 @@ struct inode *ceph_lookup_inode(struct super_block *sb, u64 ino)
 static struct dentry *__fh_to_dentry(struct super_block *sb, u64 ino)
 {
 	struct inode *inode = __lookup_inode(sb, ino);
+	int err;
+
 	if (IS_ERR(inode))
 		return ERR_CAST(inode);
-	if (inode->i_nlink == 0) {
+	/* We need LINK caps to reliably check i_nlink */
+	err = ceph_do_getattr(inode, CEPH_CAP_LINK_SHARED, false);
+	if (err)
+		return ERR_PTR(err);
+	/* -ESTALE if inode as been unlinked and no file is open */
+	if ((inode->i_nlink == 0) && (atomic_read(&inode->i_count) == 1)) {
 		iput(inode);
 		return ERR_PTR(-ESTALE);
 	}