ceph: hold extra reference to r_parent over life of request

commit 9c1c2b35f1d94de8325344c2777d7ee67492db3b upstream.

Currently, we just assume that it will stick around by virtue of the
submitter's reference, but later patches will allow the syscall to
return early and we can't rely on that reference at that point.

While I'm not aware of any reports of it, Xiubo pointed out that this
may fix a use-after-free.  If the wait for a reply times out or is
canceled via signal, and then the reply comes in after the syscall
returns, the client can end up trying to access r_parent without a
reference.

Take an extra reference to the inode when setting r_parent and release
it when releasing the request.

Cc: stable@vger.kernel.org
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: "Yan, Zheng" <zyan@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
index a5163296d9d9b10518a1942ee95c2a96f2301cf6..ee02a742fff57ad5b75fbc048e3419c5b6eb65a2 100644 (file)
--- a/fs/ceph/mds_client.c
+++ b/fs/ceph/mds_client.c
@@ -708,8 +708,10 @@ void ceph_mdsc_release_request(struct kref *kref)
                /* avoid calling iput_final() in mds dispatch threads */
                ceph_async_iput(req->r_inode);
        }
-       if (req->r_parent)
+       if (req->r_parent) {
                ceph_put_cap_refs(ceph_inode(req->r_parent), CEPH_CAP_PIN);
+               ceph_async_iput(req->r_parent);
+       }
        ceph_async_iput(req->r_target_inode);
        if (req->r_dentry)
                dput(req->r_dentry);
@@ -2670,8 +2672,10 @@ int ceph_mdsc_submit_request(struct ceph_mds_client *mdsc, struct inode *dir,
        /* take CAP_PIN refs for r_inode, r_parent, r_old_dentry */
        if (req->r_inode)
                ceph_get_cap_refs(ceph_inode(req->r_inode), CEPH_CAP_PIN);
-       if (req->r_parent)
+       if (req->r_parent) {
                ceph_get_cap_refs(ceph_inode(req->r_parent), CEPH_CAP_PIN);
+               ihold(req->r_parent);
+       }
        if (req->r_old_dentry_dir)
                ceph_get_cap_refs(ceph_inode(req->r_old_dentry_dir),
                                  CEPH_CAP_PIN);