Re: [PATCH v2] tee: fix register_shm_helper()

[Sumit Garg <sumit.garg@kernel.org>]

On Mon, Sep 22, 2025 at 10:31:58AM +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@vger.kernel.org
> Reported-by: Masami Ichikawa <masami256@gmail.com>
> Closes: https://lore.kernel.org/op-tee/CACOXgS-Bo2W72Nj1_44c7bntyNYOavnTjJAvUbEiQfq=u9W+-g@mail.gmail.com/
> Tested-by: Masami Ichikawa <masami256@gmail.com>
> Fixes: 7bdee4157591 ("tee: Use iov_iter to better support shared buffer registration")
> Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>
> ---
> Changes from v1
> - Refactor the if statement as requested by Sumit
> - Adding Tested-by: Masami Ichikawa <masami256@gmail.com
> - Link to v1:
>   https://lore.kernel.org/op-tee/20250919124217.2934718-1-jens.wiklander@linaro.org/
> ---
>  drivers/tee/tee_shm.c | 8 ++++++++
>  1 file changed, 8 insertions(+)

Reviewed-by: Sumit Garg <sumit.garg@oss.qualcomm.com>

-Sumit

> 
> diff --git a/drivers/tee/tee_shm.c b/drivers/tee/tee_shm.c
> index daf6e5cfd59a..76c54e1dc98c 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;
>  	}
>  
>  	/*
> -- 
> 2.43.0
>