lkml.org 
[lkml]   [2019]   [Dec]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: [PATCH] seccomp: Check flags on seccomp_notif is unset
On Wed, Dec 25, 2019 at 09:45:33PM +0000, Sargun Dhillon wrote:
> This patch is a small change in enforcement of the uapi for
> SECCOMP_IOCTL_NOTIF_RECV ioctl. Specificaly, the datastructure which is
> passed (seccomp_notif), has a flags member. Previously that could be
> set to a nonsense value, and we would ignore it. This ensures that
> no flags are set.
>
> Signed-off-by: Sargun Dhillon <sargun@sargun.me>
> Cc: Kees Cook <keescook@chromium.org>

I'm fine with this since we soon want to make use of the flag argument
when we add a flag to get a pidfd from the seccomp notifier on receive.
The major users I could identify already pass in seccomp_notif with all
fields set to 0. If we really break users we can always revert; this
seems very unlikely to me though.

One more question below, otherwise:

Reviewed-by: Christian Brauner <christian.brauner@ubuntu.com>

> ---
> kernel/seccomp.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/kernel/seccomp.c b/kernel/seccomp.c
> index 12d2227e5786..455925557490 100644
> --- a/kernel/seccomp.c
> +++ b/kernel/seccomp.c
> @@ -1026,6 +1026,13 @@ static long seccomp_notify_recv(struct seccomp_filter *filter,
> struct seccomp_notif unotif;
> ssize_t ret;
>
> + if (copy_from_user(&unotif, buf, sizeof(unotif)))
> + return -EFAULT;
> +
> + /* flags is reserved right now, make sure it's unset */
> + if (unotif.flags)
> + return -EINVAL;
> +

Might it make sense to use

err = copy_struct_from_user(&unotif, sizeof(unotif), buf, sizeof(unotif));
if (err)
return err;

This way we check that the whole struct is 0 and report an error as soon
as one of the members is non-zero. That's more drastic but it'd ensure
that other fields can be used in the future for whatever purposes.
It would also let us get rid of the memset() below.

> memset(&unotif, 0, sizeof(unotif));
>
> ret = down_interruptible(&filter->notif->request);
> --
> 2.20.1
>

\
 
 \ /
  Last update: 2019-12-26 12:52    [W:0.048 / U:7.704 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site