Re: [PATCH] tee: fix register_shm_helper()

[Masami Ichikawa]

Hi Jens,


On Fri, Sep 19, 2025 at 9:42 PM Jens Wiklander
<jens.wiklander@xxxxxxxxxx> 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@xxxxxxxxxxxxxxx
> Reported-by: Masami Ichikawa <masami256@xxxxxxxxx>
> Closes: https://lore.kernel.org/op-tee/CACOXgS-Bo2W72Nj1_44c7bntyNYOavnTjJAvUbEiQfq=u9W+-g@xxxxxxxxxxxxxx/
> Fixes: 7bdee4157591 ("tee: Use iov_iter to better support shared buffer registration")
> Signed-off-by: Jens Wiklander <jens.wiklander@xxxxxxxxxx>
> ---
>  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;
>         }
> --
> 2.43.0
>

Thank you for the patch. I confirmed that the patch fixes a kernel
crash caused by a NULL pointer dereference.

Tested-by: Masami Ichikawa <masami256@xxxxxxxxx>

Regrads,
--
Masami Ichikawa