linux-kernel - Re: [PATCH] tee: fix register_shm

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Message-ID: <CAHUa44FKBXjteyU=PsVfwdhNXb0msw03WD=5itxx2EKcEDwNTg@mail.gmail.com>
Date: Mon, 22 Sep 2025 08:39:09 +0200
From: Jens Wiklander <jens.wiklander@...aro.org>
To: Sumit Garg <sumit.garg@...nel.org>
Cc: linux-kernel@...r.kernel.org, op-tee@...ts.trustedfirmware.org, 
	Jerome Forissier <jerome.forissier@...aro.org>, stable@...r.kernel.org, 
	Masami Ichikawa <masami256@...il.com>
Subject: Re: [PATCH] tee: fix register_shm_helper()

On Mon, Sep 22, 2025 at 6:11 AM Sumit Garg <sumit.garg@...nel.org> wrote:
>
> On Fri, Sep 19, 2025 at 02:40:16PM +0200, Jens Wiklander wrote:
> > In register_shm_helper(), fix incorrect error handling for a call to
> > iov_iter_extract_pages(). A case is missing for when
> > iov_iter_extract_pages() only got some pages and return a number larger
> > than 0, but not the requested amount.
> >
> > This fixes a possible NULL pointer dereference following a bad input from
> > ioctl(TEE_IOC_SHM_REGISTER) where parts of the buffer isn't mapped.
> >
> > Cc: stable@...r.kernel.org
> > Reported-by: Masami Ichikawa <masami256@...il.com>
> > Closes: https://lore.kernel.org/op-tee/CACOXgS-Bo2W72Nj1_44c7bntyNYOavnTjJAvUbEiQfq=u9W+-g@mail.gmail.com/
> > Fixes: 7bdee4157591 ("tee: Use iov_iter to better support shared buffer registration")
> > Signed-off-by: Jens Wiklander <jens.wiklander@...aro.org>
> > ---
> >  drivers/tee/tee_shm.c | 11 ++++++++++-
> >  1 file changed, 10 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/tee/tee_shm.c b/drivers/tee/tee_shm.c
> > index daf6e5cfd59a..6ed7d030f4ed 100644
> > --- a/drivers/tee/tee_shm.c
> > +++ b/drivers/tee/tee_shm.c
> > @@ -316,7 +316,16 @@ register_shm_helper(struct tee_context *ctx, struct iov_iter *iter, u32 flags,
> >
> >       len = iov_iter_extract_pages(iter, &shm->pages, LONG_MAX, num_pages, 0,
> >                                    &off);
> > -     if (unlikely(len <= 0)) {
> > +     if (DIV_ROUND_UP(len + off, PAGE_SIZE) != num_pages) {
> > +             if (len > 0) {
> > +                     /*
> > +                      * If we only got a few pages, update to release
> > +                      * the correct amount below.
> > +                      */
> > +                     shm->num_pages = len / PAGE_SIZE;
> > +                     ret = ERR_PTR(-ENOMEM);
> > +                     goto err_put_shm_pages;
> > +             }
> >               ret = len ? ERR_PTR(len) : ERR_PTR(-ENOMEM);
> >               goto err_free_shm_pages;
> >       }
>
> Rather than operating directly on "len" without checking for error code
> first doesn't seems appropriate to me. How about following diff instead?

Sure, works for me.

>
> diff --git a/drivers/tee/tee_shm.c b/drivers/tee/tee_shm.c
> index daf6e5cfd59a..cb52bc51943e 100644
> --- a/drivers/tee/tee_shm.c
> +++ b/drivers/tee/tee_shm.c
> @@ -319,6 +319,14 @@ register_shm_helper(struct tee_context *ctx, struct iov_iter *iter, u32 flags,
>         if (unlikely(len <= 0)) {
>                 ret = len ? ERR_PTR(len) : ERR_PTR(-ENOMEM);
>                 goto err_free_shm_pages;
> +       } else if (DIV_ROUND_UP(len + off, PAGE_SIZE) != num_pages) {
> +               /*
> +                * If we only got a few pages, update to release the correct
> +                * amount below.
> +                */
> +               shm->num_pages = len / PAGE_SIZE;
> +               ret = ERR_PTR(-ENOMEM);
> +               goto err_put_shm_pages;
>         }
>
>         /*

Thanks,
Jens

>
> -Sumit
>
> > --
> > 2.43.0
> >