Re: [PATCH] net: don't unconditionally copy_from_user a struct ifreq for socket ioctls

[Peter Collingbourne <pcc@google.com>]

On Wed, Aug 25, 2021 at 11:39 PM Greg KH <gregkh@linuxfoundation.org> wrote:
>
> On Wed, Aug 25, 2021 at 06:27:22PM -0700, Peter Collingbourne wrote:
> > A common implementation of isatty(3) involves calling a ioctl passing
> > a dummy struct argument and checking whether the syscall failed --
> > bionic and glibc use TCGETS (passing a struct termios), and musl uses
> > TIOCGWINSZ (passing a struct winsize). If the FD is a socket, we will
> > copy sizeof(struct ifreq) bytes of data from the argument and return
> > -EFAULT if that fails. The result is that the isatty implementations
> > may return a non-POSIX-compliant value in errno in the case where part
> > of the dummy struct argument is inaccessible, as both struct termios
> > and struct winsize are smaller than struct ifreq (at least on arm64).
> >
> > Although there is usually enough stack space following the argument
> > on the stack that this did not present a practical problem up to now,
> > with MTE stack instrumentation it's more likely for the copy to fail,
> > as the memory following the struct may have a different tag.
> >
> > Fix the problem by adding an early check for whether the ioctl is a
> > valid socket ioctl, and return -ENOTTY if it isn't.
> >
> > Fixes: 44c02a2c3dc5 ("dev_ioctl(): move copyin/copyout to callers")
> > Link: https://linux-review.googlesource.com/id/I869da6cf6daabc3e4b7b82ac979683ba05e27d4d
> > Signed-off-by: Peter Collingbourne <pcc@google.com>
> > Cc: <stable@vger.kernel.org> # 4.19
> > ---
> >  include/linux/netdevice.h |  1 +
> >  net/core/dev_ioctl.c      | 64 ++++++++++++++++++++++++++++++++-------
> >  net/socket.c              |  6 +++-
> >  3 files changed, 59 insertions(+), 12 deletions(-)
> >
> > diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> > index eaf5bb008aa9..481b90ef0d32 100644
> > --- a/include/linux/netdevice.h
> > +++ b/include/linux/netdevice.h
> > @@ -4012,6 +4012,7 @@ int netdev_rx_handler_register(struct net_device *dev,
> >  void netdev_rx_handler_unregister(struct net_device *dev);
> >
> >  bool dev_valid_name(const char *name);
> > +bool is_dev_ioctl_cmd(unsigned int cmd);
>
> "is_socket_ioctl_cmd()" might be a better global name here.

SGTM, done in v2.

Peter