Matteo Rizzo <matteorizzo@xxxxxxxxxx> writes:
> Introduce a new sysctl (io_uring_disabled) which can be either 0, 1,
> or 2. When 0 (the default), all processes are allowed to create io_uring
> instances, which is the current behavior. When 1, all calls to
> io_uring_setup fail with -EPERM unless the calling process has
> CAP_SYS_ADMIN. When 2, calls to io_uring_setup fail with -EPERM
> regardless of privilege.
>
> Signed-off-by: Matteo Rizzo <matteorizzo@xxxxxxxxxx>
This looks good to me. You may also consider updating the
io_uring_setup(2) man page (part of liburing) to reflect this new
meaning for -EPERM.
Reviewed-by: Jeff Moyer <jmoyer@xxxxxxxxxx>
> ---
> Documentation/admin-guide/sysctl/kernel.rst | 19 +++++++++++++
> io_uring/io_uring.c | 30 +++++++++++++++++++++
> 2 files changed, 49 insertions(+)
>
> diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
> index 3800fab1619b..ee65f7aeb0cf 100644
> --- a/Documentation/admin-guide/sysctl/kernel.rst
> +++ b/Documentation/admin-guide/sysctl/kernel.rst
> @@ -450,6 +450,25 @@ this allows system administrators to override the
> ``IA64_THREAD_UAC_NOPRINT`` ``prctl`` and avoid logs being flooded.
>
>
> +io_uring_disabled
> +=================
> +
> +Prevents all processes from creating new io_uring instances. Enabling this
> +shrinks the kernel's attack surface.
> +
> += ==================================================================
> +0 All processes can create io_uring instances as normal. This is the
> + default setting.
> +1 io_uring creation is disabled for unprivileged processes.
> + io_uring_setup fails with -EPERM unless the calling process is
> + privileged (CAP_SYS_ADMIN). Existing io_uring instances can
> + still be used.
> +2 io_uring creation is disabled for all processes. io_uring_setup
> + always fails with -EPERM. Existing io_uring instances can still be
> + used.
> += ==================================================================
> +
> +
> kexec_load_disabled
> ===================
>
> diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
> index 1b53a2ab0a27..2343ae518546 100644
> --- a/io_uring/io_uring.c
> +++ b/io_uring/io_uring.c
> @@ -153,6 +153,22 @@ static __cold void io_fallback_tw(struct io_uring_task *tctx);
>
> struct kmem_cache *req_cachep;
>
> +static int __read_mostly sysctl_io_uring_disabled;
> +#ifdef CONFIG_SYSCTL
> +static struct ctl_table kernel_io_uring_disabled_table[] = {
> + {
> + .procname = "io_uring_disabled",
> + .data = &sysctl_io_uring_disabled,
> + .maxlen = sizeof(sysctl_io_uring_disabled),
> + .mode = 0644,
> + .proc_handler = proc_dointvec_minmax,
> + .extra1 = SYSCTL_ZERO,
> + .extra2 = SYSCTL_TWO,
> + },
> + {},
> +};
> +#endif
> +
> struct sock *io_uring_get_socket(struct file *file)
> {
> #if defined(CONFIG_UNIX)
> @@ -4000,9 +4016,18 @@ static long io_uring_setup(u32 entries, struct io_uring_params __user *params)
> return io_uring_create(entries, &p, params);
> }
>
> +static inline bool io_uring_allowed(void)
> +{
> + return sysctl_io_uring_disabled == 0 ||
> + (sysctl_io_uring_disabled == 1 && capable(CAP_SYS_ADMIN));
> +}
> +
> SYSCALL_DEFINE2(io_uring_setup, u32, entries,
> struct io_uring_params __user *, params)
> {
> + if (!io_uring_allowed())
> + return -EPERM;
> +
> return io_uring_setup(entries, params);
> }
>
> @@ -4577,6 +4602,11 @@ static int __init io_uring_init(void)
>
> req_cachep = KMEM_CACHE(io_kiocb, SLAB_HWCACHE_ALIGN | SLAB_PANIC |
> SLAB_ACCOUNT | SLAB_TYPESAFE_BY_RCU);
> +
> +#ifdef CONFIG_SYSCTL
> + register_sysctl_init("kernel", kernel_io_uring_disabled_table);
> +#endif
> +
> return 0;
> };
> __initcall(io_uring_init);
