On Wed, Jun 25, 2014 at 02:36:57PM -0700, Zach Brown wrote:
> On Wed, Jun 25, 2014 at 04:50:51PM -0400, Jeff Moyer wrote:
> >
> > From: Benjamin LaHaise <bcrl@xxxxxxxxx>
> >
> > A kernel memory disclosure was introduced in aio_read_events_ring() in v3.10
> > by commit a31ad380bed817aa25f8830ad23e1a0480fef797. The changes made to
> > aio_read_events_ring() failed to correctly limit the index into
> > ctx->ring_pages[], allowing an attacked to cause the subsequent kmap() of
> > an arbitrary page with a copy_to_user() to copy the contents into userspace.
> > This vulnerability has been assigned CVE-2014-0206. Thanks to Mateusz and
> > Petr for disclosing this issue.
> >
> > [jmoyer@xxxxxxxxxx: backported to 3.10]
> > Signed-off-by: Benjamin LaHaise <bcrl@xxxxxxxxx>
> > Signed-off-by: Jeff Moyer <jmoyer@xxxxxxxxxx>
> > Cc: Mateusz Guzik <mguzik@xxxxxxxxxx>
> > Cc: Petr Matousek <pmatouse@xxxxxxxxxx>
> > Cc: Kent Overstreet <kmo@xxxxxxxxxxxxx>
> > Cc: stable@xxxxxxxxxxxxxxx
> > ---
> > aio.c | 2 ++
> > 1 file changed, 2 insertions(+)
> >
> > diff --git a/fs/aio.c b/fs/aio.c
> > index e66b948..872fd26 100644
> > --- a/fs/aio.c
> > +++ b/fs/aio.c
> > @@ -717,6 +717,8 @@ static long aio_read_events_ring(struct kioctx *ctx,
> > if (head == ctx->tail)
> > goto out;
> >
> > + head %= ctx->nr_events;
> > +
> > while (ret < nr) {
> > long avail;
> > struct io_event *ev;
>
>
> Hmm. Are you sure it's safe to clamp head but not ctx->tail? The body
> of the loop still has:
>
> avail = (head <= ctx->tail ? ctx->tail : ctx->nr_events) - head;
Oops, nope, my mistake! ctx->tail is still stored modulo nr_events. I
somehow had it in my head that the giant series patches had changed
that. Never mind. Carry on :).
- z
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