Commit 76d3ccec authored by Matteo Rizzo's avatar Matteo Rizzo Committed by Jens Axboe
Browse files

io_uring: add a sysctl to disable io_uring system-wide 



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, io_uring creation is
disabled (io_uring_setup() will fail with -EPERM) for unprivileged
processes not in the kernel.io_uring_group group.  When 2, calls to
io_uring_setup() fail with -EPERM regardless of privilege.

Signed-off-by: default avatarMatteo Rizzo <matteorizzo@google.com>
[JEM: modified to add io_uring_group]
Signed-off-by: default avatarJeff Moyer <jmoyer@redhat.com>
Link: https://lore.kernel.org/r/x49y1i42j1z.fsf@segfault.boston.devel.redhat.com


Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 32f5dea0

Documentation/admin-guide/sysctl/kernel.rst

+29 −0
Original line number Diff line number Diff line
@@ -450,6 +450,35 @@ 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 (io_uring_setup() will fail with

  -EPERM) for unprivileged processes not in the io_uring_group group.

  Existing io_uring instances can still be used.  See the

  documentation for io_uring_group for more information.

2 io_uring creation is disabled for all processes. io_uring_setup()

  always fails with -EPERM. Existing io_uring instances can still be

  used.

= ======================================================================





io_uring_group

==============



When io_uring_disabled is set to 1, a process must either be

privileged (CAP_SYS_ADMIN) or be in the io_uring_group group in order

to create an io_uring instance.  If io_uring_group is set to -1 (the

default), only processes with the CAP_SYS_ADMIN capability may create

io_uring instances.





kexec_load_disabled

===================

io_uring/io_uring.c

+50 −0
Original line number Diff line number Diff line
@@ -150,6 +150,31 @@ static void io_queue_sqe(struct io_kiocb *req); 


struct kmem_cache *req_cachep;



static int __read_mostly sysctl_io_uring_disabled;

static int __read_mostly sysctl_io_uring_group = -1;



#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,

	},

	{

		.procname	= "io_uring_group",

		.data		= &sysctl_io_uring_group,

		.maxlen		= sizeof(gid_t),

		.mode		= 0644,

		.proc_handler	= proc_dointvec,

	},

	{},

};

#endif



struct sock *io_uring_get_socket(struct file *file)

{

#if defined(CONFIG_UNIX)
@@ -4070,9 +4095,30 @@ 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)

{

	int disabled = READ_ONCE(sysctl_io_uring_disabled);

	kgid_t io_uring_group;



	if (disabled == 2)

		return false;



	if (disabled == 0 || capable(CAP_SYS_ADMIN))

		return true;



	io_uring_group = make_kgid(&init_user_ns, sysctl_io_uring_group);

	if (!gid_valid(io_uring_group))

		return false;



	return in_group_p(io_uring_group);

}



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);

}
@@ -4666,6 +4712,10 @@ static int __init io_uring_init(void) 
				offsetof(struct io_kiocb, cmd.data),

				sizeof_field(struct io_kiocb, cmd.data), NULL);



#ifdef CONFIG_SYSCTL

	register_sysctl_init("kernel", kernel_io_uring_disabled_table);

#endif



	return 0;

};

__initcall(io_uring_init);