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Commit cf7bb109 authored by Xiubo Li's avatar Xiubo Li Committed by Greg Kroah-Hartman
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ceph: fix use-after-free bug for inodes when flushing capsnaps 

commit 409e873ea3c1fd3079909718bbeb06ac1ec7f38b upstream.

There is a race between capsnaps flush and removing the inode from
'mdsc->snap_flush_list' list:

   == Thread A ==                     == Thread B ==
ceph_queue_cap_snap()
 -> allocate 'capsnapA'
 ->ihold('&ci->vfs_inode')
 ->add 'capsnapA' to 'ci->i_cap_snaps'
 ->add 'ci' to 'mdsc->snap_flush_list'
    ...
   == Thread C ==
ceph_flush_snaps()
 ->__ceph_flush_snaps()
  ->__send_flush_snap()
                                handle_cap_flushsnap_ack()
                                 ->iput('&ci->vfs_inode')
                                   this also will release 'ci'
                                    ...
				      == Thread D ==
                                ceph_handle_snap()
                                 ->flush_snaps()
                                  ->iterate 'mdsc->snap_flush_list'
                                   ->get the stale 'ci'
 ->remove 'ci' from                ->ihold(&ci->vfs_inode) this
   'mdsc->snap_flush_list'           will WARNING

To fix this we will increase the inode's i_count ref when adding 'ci'
to the 'mdsc->snap_flush_list' list.

[ idryomov: need_put int -> bool ]

Cc: stable@vger.kernel.org
Link: https://bugzilla.redhat.com/show_bug.cgi?id=2209299


Signed-off-by: default avatarXiubo Li <xiubli@redhat.com>
Reviewed-by: default avatarMilind Changire <mchangir@redhat.com>
Reviewed-by: default avatarIlya Dryomov <idryomov@gmail.com>
Signed-off-by: default avatarIlya Dryomov <idryomov@gmail.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 46a036d2

fs/ceph/caps.c

+6 −0
Original line number Diff line number Diff line
@@ -1554,6 +1554,7 @@ void ceph_flush_snaps(struct ceph_inode_info *ci, 
	struct inode *inode = &ci->vfs_inode;

	struct ceph_mds_client *mdsc = ceph_inode_to_client(inode)->mdsc;

	struct ceph_mds_session *session = NULL;

	bool need_put = false;

	int mds;



	dout("ceph_flush_snaps %p\n", inode);
@@ -1607,8 +1608,13 @@ void ceph_flush_snaps(struct ceph_inode_info *ci, 
	}

	/* we flushed them all; remove this inode from the queue */

	spin_lock(&mdsc->snap_flush_lock);

	if (!list_empty(&ci->i_snap_flush_item))

		need_put = true;

	list_del_init(&ci->i_snap_flush_item);

	spin_unlock(&mdsc->snap_flush_lock);



	if (need_put)

		iput(inode);

}



/*

fs/ceph/snap.c

+3 −1
Original line number Diff line number Diff line
@@ -623,8 +623,10 @@ int __ceph_finish_cap_snap(struct ceph_inode_info *ci, 
	     capsnap->size);



	spin_lock(&mdsc->snap_flush_lock);

	if (list_empty(&ci->i_snap_flush_item))

	if (list_empty(&ci->i_snap_flush_item)) {

		ihold(inode);

		list_add_tail(&ci->i_snap_flush_item, &mdsc->snap_flush_list);

	}

	spin_unlock(&mdsc->snap_flush_lock);

	return 1;  /* caller may want to ceph_flush_snaps */

}