Re: [PATCH] tee: add overflow check in tee_ioctl_shm_register()

[Greg KH <gregkh@linuxfoundation.org>]

On Tue, Aug 23, 2022 at 09:00:43AM +0200, Jens Wiklander wrote:
> On Mon, Aug 22, 2022 at 4:57 PM Greg KH <gregkh@linuxfoundation.org> wrote:
> >
> > On Mon, Aug 22, 2022 at 04:29:05PM +0200, Jens Wiklander wrote:
> > > On Mon, Aug 22, 2022 at 3:32 PM Greg KH <gregkh@linuxfoundation.org> wrote:
> > > >
> > > > On Mon, Aug 22, 2022 at 03:12:27PM +0200, Jens Wiklander wrote:
> > > > > commit 573ae4f13f630d6660008f1974c0a8a29c30e18a upstream.
> > > > >
> > > > > With special lengths supplied by user space, tee_shm_register() has
> > > > > an integer overflow when calculating the number of pages covered by a
> > > > > supplied user space memory region.
> > > > >
> > > > > This may cause pin_user_pages_fast() to do a NULL pointer dereference.
> > > > >
> > > > > Fix this by adding an an explicit call to access_ok() in
> > > > > tee_ioctl_shm_register() to catch an invalid user space address early.
> > > > >
> > > > > Fixes: 033ddf12bcf5 ("tee: add register user memory")
> > > > > Cc: stable@vger.kernel.org # 5.4
> > > > > Cc: stable@vger.kernel.org # 5.10
> > > > > Reported-by: Nimish Mishra <neelam.nimish@gmail.com>
> > > > > Reported-by: Anirban Chakraborty <ch.anirban00727@gmail.com>
> > > > > Reported-by: Debdeep Mukhopadhyay <debdeep.mukhopadhyay@gmail.com>
> > > > > Suggested-by: Jerome Forissier <jerome.forissier@linaro.org>
> > > > > Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
> > > > > [JW: backport to stable 5.4 and 5.10 + update commit message]
> > > >
> > > > You already sent me a 5.4 version here:
> > > >         https://lore.kernel.org/r/20220822092621.3691771-1-jens.wiklander@linaro.org
> > > >
> > > > And I applied that.
> > > >
> > > > And for 5.10, it's already in the tree as commit 578c349570d2 ("tee: add
> > > > overflow check in register_shm_helper()") and was in the 5.10.137
> > > > release.
> > > >
> > > > > Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>
> > > > > ---
> > > > >  drivers/tee/tee_core.c | 3 +++
> > > > >  1 file changed, 3 insertions(+)
> > > > >
> > > > > diff --git a/drivers/tee/tee_core.c b/drivers/tee/tee_core.c
> > > > > index a7ccd4d2bd10..2db144d2d26f 100644
> > > > > --- a/drivers/tee/tee_core.c
> > > > > +++ b/drivers/tee/tee_core.c
> > > > > @@ -182,6 +182,9 @@ tee_ioctl_shm_register(struct tee_context *ctx,
> > > > >       if (data.flags)
> > > > >               return -EINVAL;
> > > > >
> > > > > +     if (!access_ok((void __user *)(unsigned long)data.addr, data.length))
> > > > > +             return -EFAULT;
> > > >
> > > > What I took in 5.10.137 was:
> > > >
> > > > +       if (!access_ok((void __user *)addr, length))
> > > > +               return ERR_PTR(-EFAULT);
> > > >
> > > > Should I fix it up to look like what you sent here instead?
> > >
> > > Yes, please.
> >
> > Ok, no, that does not work on 5.10.y at all, it blows up with the
> > obvious issue that there is no data pointer in this function.  It's also
> > in a different file, drivers/tee/tee_shm.c
> >
> > So I'm going to leave 5.10.y alone for now, I think it's fixed.
> 
> It works somewhat, but there's the potential memory leak that Pavel
> Machek pointed out,
> https://lore.kernel.org/lkml/20220822111546.GA7795@duo.ucw.cz/ .
> 
> The 5.4 patch has a better approach since it verifies the supplied
> address range early before we do anything that must be undone on
> error.
> The 5.4 patch changes  tee_ioctl_shm_register() instead, which is the
> function one step up in the call chain. This approach should be taken
> for all kernels before 53e16519c2ec ("tee: replace
> tee_shm_register()"), that is, before v5.18 if I'm reading the git log
> correctly.
> 
> access_ok() went from taking three arguments to two sometime after
> v4.19, why that patch is slightly different.

Ok, can you send me a new fix-up patch, on top of the latest 5.10.y
release, to resolve the 5.10 issue?

thanks,

greg k-h