Hi
On Fri, May 1, 2020 at 8:29 PM Colin Walters <walt...@verbum.org> wrote:
>
> I'd like to make use of virtiofs as part of our tooling in
> https://github.com/coreos/coreos-assembler
> Most of the code runs as non-root today; qemu also runs as non-root.
> We use 9p right now.
>
> virtiofsd's builtin sandboxing effectively assumes it runs as
> root.
>
> First, change the code to use `clone()` and not `unshare()+fork()`.
>
> Next, automatically use `CLONE_NEWUSER` if we're running as non root.
>
> This is similar logic to that in https://github.com/containers/bubblewrap
> (Which...BTW, it could make sense for virtiofs to depend on bubblewrap
> and re-exec itself rather than re-implementing the containerization
> itself)
>
Now that systemd-nspawn works without privileges, isn't that also a
solution? One that would fit both system and session level
permissions, and integration with other services?
> Signed-off-by: Colin Walters <walt...@verbum.org>
> ---
> tools/virtiofsd/passthrough_ll.c | 26 +++++++++++++++++++++-----
> 1 file changed, 21 insertions(+), 5 deletions(-)
>
> diff --git a/tools/virtiofsd/passthrough_ll.c
> b/tools/virtiofsd/passthrough_ll.c
> index 4c35c95b25..468617f6d6 100644
> --- a/tools/virtiofsd/passthrough_ll.c
> +++ b/tools/virtiofsd/passthrough_ll.c
> @@ -2530,6 +2530,21 @@ static void print_capabilities(void)
> printf("}\n");
> }
>
> +/* Copied from bubblewrap */
> +static int
> +raw_clone(unsigned long flags, void *child_stack)
> +{
> +#if defined(__s390__) || defined(__CRIS__)
> + /*
> + * On s390 and cris the order of the first and second arguments
> + * of the raw clone() system call is reversed.
> + */
> + return (int) syscall(__NR_clone, child_stack, flags);
> +#else
> + return (int) syscall(__NR_clone, flags, child_stack);
> +#endif
> +}
> +
> /*
> * Move to a new mount, net, and pid namespaces to isolate this process.
> */
> @@ -2547,14 +2562,15 @@ static void setup_namespaces(struct lo_data *lo,
> struct fuse_session *se)
> * an empty network namespace to prevent TCP/IP and other network
> * activity in case this process is compromised.
> */
> - if (unshare(CLONE_NEWPID | CLONE_NEWNS | CLONE_NEWNET) != 0) {
> - fuse_log(FUSE_LOG_ERR, "unshare(CLONE_NEWPID | CLONE_NEWNS): %m\n");
> - exit(1);
> + int clone_flags = SIGCHLD | CLONE_NEWPID | CLONE_NEWNS | CLONE_NEWNET;
> + /* If we're non root, we need a new user namespace */
> + if (getuid() != 0) {
> + clone_flags |= CLONE_NEWUSER;
> }
>
> - child = fork();
> + child = raw_clone(clone_flags, NULL);
> if (child < 0) {
> - fuse_log(FUSE_LOG_ERR, "fork() failed: %m\n");
> + fuse_log(FUSE_LOG_ERR, "clone() failed: %m\n");
> exit(1);
> }
> if (child > 0) {
> --
> 2.24.1
>
>
--
Marc-André Lureau
