Re: [PATCH v2 2/2] seccomp: Check that seccomp_notif is zeroed out by the user

Aleksa Sarai
2019-12-28T02:06:43Z

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On 2019-12-28, Sargun Dhillon <sargun@sargun.me> wrote:
> This patch is a small change in enforcement of the uapi for
> SECCOMP_IOCTL_NOTIF_RECV ioctl. Specifically, the datastructure which
> is passed (seccomp_notif) must be zeroed out. Previously any of its
> members could be set to nonsense values, and we would ignore it.
>
> This ensures all fields are set to their zero value.
>
> This relies on the seccomp_notif datastructure to not have
> any unnamed padding, as it is valid to initialize the datastructure
> as:
>
> struct seccomp_notif notif = {};
>
> This only initializes named members to their 0-value [1].
>
> [1]: https://lore.kernel.org/lkml/20191227023131.klnobtlfgeqcmvbb@yavin.dot.cyphar.com/
>
> Signed-off-by: Sargun Dhillon <sargun@sargun.me>
> Cc: Kees Cook <keescook@chromium.org>

Looks good.

Reviewed-by: Aleksa Sarai <cyphar@cyphar.com>

> ---
> kernel/seccomp.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/kernel/seccomp.c b/kernel/seccomp.c
> index 12d2227e5786..4fd73cbdd01e 100644
> --- a/kernel/seccomp.c
> +++ b/kernel/seccomp.c
> @@ -1026,6 +1026,12 @@ static long seccomp_notify_recv(struct seccomp_filter *filter,
> struct seccomp_notif unotif;
> ssize_t ret;
>
> + ret = check_zeroed_user(buf, sizeof(unotif));
> + if (ret < 0)
> + return ret;
> + if (!ret)
> + return -EINVAL;
> +
> memset(&unotif, 0, sizeof(unotif));
>
> ret = down_interruptible(&filter->notif->request);
> --
> 2.20.1
>

--
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
<https://www.cyphar.com/>

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