linux-kernel - Re: [PATCH v2 2/2] seccomp: Check that seccomp

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Message-ID: <20191228020643.jb2kn5wztwnrpr74@yavin.dot.cyphar.com>
Date:   Sat, 28 Dec 2019 13:06:43 +1100
From:   Aleksa Sarai <cyphar@...har.com>
To:     Sargun Dhillon <sargun@...gun.me>
Cc:     linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        tycho@...ho.ws, jannh@...gle.com, christian.brauner@...ntu.com,
        keescook@...omium.org
Subject: Re: [PATCH v2 2/2] seccomp: Check that seccomp_notif is zeroed out
 by the user

On 2019-12-28, Sargun Dhillon <sargun@...gun.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@...gun.me>
> Cc: Kees Cook <keescook@...omium.org>

Looks good.

Reviewed-by: Aleksa Sarai <cyphar@...har.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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