[Linux-kernel-mentees] [PATCH net] rds: Prevent kernel-infoleak in rds_notify_queue_get()

[Andy Shevchenko]

On Friday, July 31, 2020, Leon Romanovsky <leon at kernel.org> wrote:

> On Thu, Jul 30, 2020 at 03:20:26PM -0400, Peilin Ye wrote:
> > rds_notify_queue_get() is potentially copying uninitialized kernel stack
> > memory to userspace since the compiler may leave a 4-byte hole at the end
> > of `cmsg`.
> >
> > In 2016 we tried to fix this issue by doing `= { 0 };` on `cmsg`, which
> > unfortunately does not always initialize that 4-byte hole. Fix it by
> using
> > memset() instead.
>
> Of course, this is the difference between "{ 0 }" and "{}" initializations.
>
> >
> > Cc: stable at vger.kernel.org
> > Fixes: f037590fff30 ("rds: fix a leak of kernel memory")
> > Fixes: bdbe6fbc6a2f ("RDS: recv.c")
> > Suggested-by: Dan Carpenter <dan.carpenter at oracle.com>
> > Signed-off-by: Peilin Ye <yepeilin.cs at gmail.com>
> > ---
> > Note: the "real" copy_to_user() happens in put_cmsg(), where
> > `cmlen - sizeof(*cm)` equals to `sizeof(cmsg)`.
> >
> > Reference: https://lwn.net/Articles/417989/
> >
> > $ pahole -C "rds_rdma_notify" net/rds/recv.o
> > struct rds_rdma_notify {
> >       __u64                      user_token;           /*     0     8 */
> >       __s32                      status;               /*     8     4 */
> >
> >       /* size: 16, cachelines: 1, members: 2 */
> >       /* padding: 4 */
> >       /* last cacheline: 16 bytes */
> > };
> >
> >  net/rds/recv.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/net/rds/recv.c b/net/rds/recv.c
> > index c8404971d5ab..aba4afe4dfed 100644
> > --- a/net/rds/recv.c
> > +++ b/net/rds/recv.c
> > @@ -450,12 +450,13 @@ static int rds_still_queued(struct rds_sock *rs,
> struct rds_incoming *inc,
> >  int rds_notify_queue_get(struct rds_sock *rs, struct msghdr *msghdr)
> >  {
> >       struct rds_notifier *notifier;
> > -     struct rds_rdma_notify cmsg = { 0 }; /* fill holes with zero */
> > +     struct rds_rdma_notify cmsg;
> >       unsigned int count = 0, max_messages = ~0U;
> >       unsigned long flags;
> >       LIST_HEAD(copy);
> >       int err = 0;
> >
> > +     memset(&cmsg, 0, sizeof(cmsg)); /* fill holes with zero */
>
> It works, but the right solution is to drop 0 from cmsg initialization
> and write "struct rds_rdma_notify cmsg = {};" without any memset.



No, the right solution is to use memset() over gcc extension.


>
> Thanks
>


-- 
With Best Regards,
Andy Shevchenko
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.linuxfoundation.org/pipermail/linux-kernel-mentees/attachments/20200731/b78a1ee0/attachment.html>