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Message-ID: <x49wmxuub14.fsf@segfault.boston.devel.redhat.com>
Date: Wed, 16 Aug 2023 13:55:51 -0400
From: Jeff Moyer <jmoyer@...hat.com>
To: matteorizzo@...gle.com, linux-doc@...r.kernel.org,
linux-kernel@...r.kernel.org, io-uring@...r.kernel.org,
axboe@...nel.dk, asml.silence@...il.com
Cc: corbet@....net, akpm@...ux-foundation.org, keescook@...omium.org,
ribalda@...omium.org, rostedt@...dmis.org, jannh@...gle.com,
chenhuacai@...nel.org, gpiccoli@...lia.com, ldufour@...ux.ibm.com,
evn@...gle.com, poprdi@...gle.com, jordyzomer@...gle.com,
krisman@...e.de, andres@...razel.de
Subject: [PATCH v4] io_uring: add a sysctl to disable io_uring system-wide
From: Matteo Rizzo <matteorizzo@...gle.com>
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 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: Matteo Rizzo <matteorizzo@...gle.com>
[JEM: modified to add io_uring_group]
Signed-off-by: Jeff Moyer <jmoyer@...hat.com>
---
v4:
* Add a kernel.io_uring_group sysctl to hold a group id that is allowed
to use io_uring. One thing worth pointing out is that, when a group
is specified, only users in that group can create an io_uring. That
means that if the root user is not in that group, root can not make
use of io_uring.
I also wrote unit tests for liburing. I'll post that as well if there
is consensus on this approach.
Matteo, you didn't reply to Jens' message about pulling the patch, so
I figured you got busy, so I picked up the patch. I hope you're okay
with the signoff.
v3:
* Fix the commit message
* Use READ_ONCE in io_uring_allowed to avoid races
* Add reviews
v2:
* Documentation style fixes
* Add a third level that only disables io_uring for unprivileged
processes
diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
index 3800fab1619b..dc4b19f2f2cb 100644
--- a/Documentation/admin-guide/sysctl/kernel.rst
+++ b/Documentation/admin-guide/sysctl/kernel.rst
@@ -450,6 +450,34 @@ 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 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 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
===================
diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 93db3e4e7b68..fbee37fb9bad 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -152,6 +152,31 @@ static void __io_submit_flush_completions(struct io_ring_ctx *ctx);
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)
@@ -4040,9 +4065,31 @@ 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 == 0)
+ return true;
+
+ if (disabled == 2)
+ return false;
+
+ /* default to root only */
+ io_uring_group = make_kgid(&init_user_ns, sysctl_io_uring_group);
+ if (!gid_valid(io_uring_group))
+ return capable(CAP_SYS_ADMIN);
+
+ 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);
}
@@ -4617,6 +4664,11 @@ 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);
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