Re: [PATCH v3 1/4] fs, net: Standardize on file_receive helper to move fds across processes

Sargun Dhillon
2020-06-11T04:41:50Z

On Wed, Jun 10, 2020 at 07:59:55PM -0700, Kees Cook wrote:
>
> Yeah, that seems reasonable. Here's the diff for that part:
>
> diff --git a/include/uapi/linux/seccomp.h b/include/uapi/linux/seccomp.h
> index 7b6028b399d8..98bf19b4e086 100644
> --- a/include/uapi/linux/seccomp.h
> +++ b/include/uapi/linux/seccomp.h
> @@ -118,7 +118,6 @@ struct seccomp_notif_resp {
>
> /**
> * struct seccomp_notif_addfd
> - * @size: The size of the seccomp_notif_addfd datastructure
> * @id: The ID of the seccomp notification
> * @flags: SECCOMP_ADDFD_FLAG_*
> * @srcfd: The local fd number
> @@ -126,7 +125,6 @@ struct seccomp_notif_resp {
> * @newfd_flags: The O_* flags the remote FD should have applied
> */
> struct seccomp_notif_addfd {
> - __u64 size;
> __u64 id;
> __u32 flags;
> __u32 srcfd;
> diff --git a/kernel/seccomp.c b/kernel/seccomp.c
> index 3c913f3b8451..00cbdad6c480 100644
> --- a/kernel/seccomp.c
> +++ b/kernel/seccomp.c
> @@ -1297,14 +1297,9 @@ static long seccomp_notify_addfd(struct seccomp_filter *filter,
> struct seccomp_notif_addfd addfd;
> struct seccomp_knotif *knotif;
> struct seccomp_kaddfd kaddfd;
> - u64 size;
> int ret;
>
> - ret = get_user(size, &uaddfd->size);
> - if (ret)
> - return ret;
> -
> - ret = copy_struct_from_user(&addfd, sizeof(addfd), uaddfd, size);
> + ret = copy_from_user(&addfd, uaddfd, sizeof(addfd));
> if (ret)
> return ret;
>
>
Looks good to me. If we ever change the size of this struct, we can do the work
then to copy_struct_from_user.

> >
> > ----
> > +#define SECCOMP_IOCTL_NOTIF_ADDFD SECCOMP_IOR(3, \
> > + struct seccomp_notif_addfd)
> >
> > Lastly, what I believe to be a small mistake, it should be SECCOMP_IOW, based on
> > the documentation in ioctl.h -- "_IOW means userland is writing and kernel is
> > reading."
>
> Oooooh. Yeah; good catch. Uhm, that means SECCOMP_IOCTL_NOTIF_ID_VALID
> is wrong too, yes? Tycho, Christian, how disruptive would this be to
> fix? (Perhaps support both and deprecate the IOR version at some point
> in the future?)
I think at a minimum we should change the uapi, and accept both (for now). Maybe
a pr_warn_once telling people not to use the old one.

I can do the patch, if you want.
>
> Diff for just addfd's change:
>
> diff --git a/include/uapi/linux/seccomp.h b/include/uapi/linux/seccomp.h
> index 7b6028b399d8..98bf19b4e086 100644
> --- a/include/uapi/linux/seccomp.h
> +++ b/include/uapi/linux/seccomp.h
> @@ -146,7 +144,7 @@ struct seccomp_notif_addfd {
> struct seccomp_notif_resp)
> #define SECCOMP_IOCTL_NOTIF_ID_VALID SECCOMP_IOR(2, __u64)
> /* On success, the return value is the remote process's added fd number */
> -#define SECCOMP_IOCTL_NOTIF_ADDFD SECCOMP_IOR(3, \
> +#define SECCOMP_IOCTL_NOTIF_ADDFD SECCOMP_IOW(3, \
> struct seccomp_notif_addfd)
>
> #endif /* _UAPI_LINUX_SECCOMP_H */
>
> --
> Kees Cook
Looks good. Thank you.