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[PATCH] tee: fix register_shm_helper()

Jens Wiklander posted 1 patch 3 months ago
There is a newer version of this series
drivers/tee/tee_shm.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
[PATCH] tee: fix register_shm_helper()
Posted by Jens Wiklander 3 months ago 
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/
Fixes: 7bdee4157591 ("tee: Use iov_iter to better support shared buffer registration")
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.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;
 	}
-- 
2.43.0
Re: [PATCH] tee: fix register_shm_helper()
Posted by Sumit Garg 2 months, 3 weeks ago 
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@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/
> Fixes: 7bdee4157591 ("tee: Use iov_iter to better support shared buffer registration")
> Signed-off-by: Jens Wiklander <jens.wiklander@linaro.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?

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;
        }
 
        /*

-Sumit

> -- 
> 2.43.0
>
Re: [PATCH] tee: fix register_shm_helper()
Posted by Jens Wiklander 2 months, 3 weeks ago 
On Mon, Sep 22, 2025 at 6:11 AM Sumit Garg <sumit.garg@kernel.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@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/
> > Fixes: 7bdee4157591 ("tee: Use iov_iter to better support shared buffer registration")
> > Signed-off-by: Jens Wiklander <jens.wiklander@linaro.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
> >
Re: [PATCH] tee: fix register_shm_helper()
Posted by Masami Ichikawa 2 months, 4 weeks ago 
Hi Jens,


On Fri, Sep 19, 2025 at 9:42 PM Jens Wiklander
<jens.wiklander@linaro.org> 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/
> Fixes: 7bdee4157591 ("tee: Use iov_iter to better support shared buffer registration")
> Signed-off-by: Jens Wiklander <jens.wiklander@linaro.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;
>         }
> --
> 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@gmail.com>

Regrads,
--
Masami Ichikawa

Patchew 2.1-devel-b67e4c2

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