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    Subject[PATCH 5.4 037/104] ceph: hold extra reference to r_parent over life of request
    Date
    From: Jeff Layton <jlayton@kernel.org>

    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>

    ---
    fs/ceph/mds_client.c | 8 ++++++--
    1 file changed, 6 insertions(+), 2 deletions(-)

    --- a/fs/ceph/mds_client.c
    +++ b/fs/ceph/mds_client.c
    @@ -708,8 +708,10 @@ void ceph_mdsc_release_request(struct kr
    /* 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
    /* 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);

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