Re: [PATCH] ceph: fix corruption when using page_count 0 page in rbd

[Sage Weil]

On Tue, 6 May 2014, Ilya Dryomov wrote:
> On Wed, Apr 23, 2014 at 8:35 AM, Chunwei Chen <tuxoko@xxxxxxxxx> wrote:
> > It has been reported that using ZFSonLinux on rbd will result in memory
> > corruption. The bug report can be found here:
> >
> > https://github.com/zfsonlinux/spl/issues/241
> > http://tracker.ceph.com/issues/7790
> >
> > The reason is that ZFS will send pages with page_count 0 into rbd, which in
> > turns send them to tcp_sendpage. However, tcp_sendpage cannot deal with
> > page_count 0, as it will do get_page and put_page, and erroneously free the
> > page.
> >
> > This type of issue has been noted before, and handled in iscsi, drbd,
> > etc. So, rbd should also handle this. This fix address this issue by fall back
> > to slower sendmsg when page_count 0 detected.
> >
> > Cc: Sage Weil <sage@xxxxxxxxxxx>
> > Cc: Yehuda Sadeh <yehuda@xxxxxxxxxxx>
> > Cc: stable@xxxxxxxxxxxxxxx
> > Signed-off-by: Chunwei Chen <tuxoko@xxxxxxxxx>
> > ---
> >  net/ceph/messenger.c | 20 +++++++++++++++++++-
> >  1 file changed, 19 insertions(+), 1 deletion(-)
> >
> > diff --git a/net/ceph/messenger.c b/net/ceph/messenger.c
> > index 4f55f9c..9a964e7 100644
> > --- a/net/ceph/messenger.c
> > +++ b/net/ceph/messenger.c
> > @@ -557,7 +557,7 @@ static int ceph_tcp_sendmsg(struct socket *sock, struct kvec *iov,
> >         return r;
> >  }
> >
> > -static int ceph_tcp_sendpage(struct socket *sock, struct page *page,
> > +static int __ceph_tcp_sendpage(struct socket *sock, struct page *page,
> >                      int offset, size_t size, bool more)
> >  {
> >         int flags = MSG_DONTWAIT | MSG_NOSIGNAL | (more ? MSG_MORE : MSG_EOR);
> > @@ -570,6 +570,24 @@ static int ceph_tcp_sendpage(struct socket *sock, struct page *page,
> >         return ret;
> >  }
> >
> > +static int ceph_tcp_sendpage(struct socket *sock, struct page *page,
> > +                    int offset, size_t size, bool more)
> > +{
> > +       int ret;
> > +       struct kvec iov;
> > +
> > +       /* sendpage cannot properly handle pages with page_count == 0,
> > +        * we need to fallback to sendmsg if that's the case */
> > +       if (page_count(page) >= 1)
> > +               return __ceph_tcp_sendpage(sock, page, offset, size, more);
> > +
> > +       iov.iov_base = kmap(page) + offset;
> > +       iov.iov_len = size;
> > +       ret = ceph_tcp_sendmsg(sock, &iov, 1, size, more);
> > +       kunmap(page);
> > +
> > +       return ret;
> > +}
> 
> Looks good to me.  Have you tested it with pre "Fix crash when using
> ZFS on Ceph rbd" ZFS?

Once this looks ready, we should perhaps stick it in for-linus so that it 
can go into 3.15.

sage
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