Commit 08389d88 authored by Daniel Borkmann's avatar Daniel Borkmann Committed by Alexei Starovoitov
Browse files

bpf: Add kconfig knob for disabling unpriv bpf by default 



Add a kconfig knob which allows for unprivileged bpf to be disabled by default.
If set, the knob sets /proc/sys/kernel/unprivileged_bpf_disabled to value of 2.

This still allows a transition of 2 -> {0,1} through an admin. Similarly,
this also still keeps 1 -> {1} behavior intact, so that once set to permanently
disabled, it cannot be undone aside from a reboot.

We've also added extra2 with max of 2 for the procfs handler, so that an admin
still has a chance to toggle between 0 <-> 2.

Either way, as an additional alternative, applications can make use of CAP_BPF
that we added a while ago.

Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/74ec548079189e4e4dffaeb42b8987bb3c852eee.1620765074.git.daniel@iogearbox.net
parent b24abcff

Documentation/admin-guide/sysctl/kernel.rst

+14 −3
Original line number Diff line number Diff line
@@ -1457,11 +1457,22 @@ unprivileged_bpf_disabled 
=========================



Writing 1 to this entry will disable unprivileged calls to ``bpf()``;

once disabled, calling ``bpf()`` without ``CAP_SYS_ADMIN`` will return

``-EPERM``.

once disabled, calling ``bpf()`` without ``CAP_SYS_ADMIN`` or ``CAP_BPF``

will return ``-EPERM``. Once set to 1, this can't be cleared from the

running kernel anymore.



Once set, this can't be cleared.

Writing 2 to this entry will also disable unprivileged calls to ``bpf()``,

however, an admin can still change this setting later on, if needed, by

writing 0 or 1 to this entry.



If ``BPF_UNPRIV_DEFAULT_OFF`` is enabled in the kernel config, then this

entry will default to 2 instead of 0.



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

0 Unprivileged calls to ``bpf()`` are enabled

1 Unprivileged calls to ``bpf()`` are disabled without recovery

2 Unprivileged calls to ``bpf()`` are disabled

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



watchdog

========

kernel/bpf/Kconfig

+10 −0
Original line number Diff line number Diff line
@@ -61,6 +61,16 @@ config BPF_JIT_DEFAULT_ON 
	def_bool ARCH_WANT_DEFAULT_BPF_JIT || BPF_JIT_ALWAYS_ON

	depends on HAVE_EBPF_JIT && BPF_JIT



config BPF_UNPRIV_DEFAULT_OFF

	bool "Disable unprivileged BPF by default"

	depends on BPF_SYSCALL

	help

	  Disables unprivileged BPF by default by setting the corresponding

	  /proc/sys/kernel/unprivileged_bpf_disabled knob to 2. An admin can

	  still reenable it by setting it to 0 later on, or permanently

	  disable it by setting it to 1 (from which no other transition to

	  0 is possible anymore).



source "kernel/bpf/preload/Kconfig"



config BPF_LSM

kernel/bpf/syscall.c

+2 −1
Original line number Diff line number Diff line
@@ -50,7 +50,8 @@ static DEFINE_SPINLOCK(map_idr_lock); 
static DEFINE_IDR(link_idr);

static DEFINE_SPINLOCK(link_idr_lock);



int sysctl_unprivileged_bpf_disabled __read_mostly;

int sysctl_unprivileged_bpf_disabled __read_mostly =

	IS_BUILTIN(CONFIG_BPF_UNPRIV_DEFAULT_OFF) ? 2 : 0;



static const struct bpf_map_ops * const bpf_map_types[] = {

#define BPF_PROG_TYPE(_id, _name, prog_ctx_type, kern_ctx_type)

kernel/sysctl.c

+24 −5
Original line number Diff line number Diff line
@@ -225,7 +225,27 @@ static int bpf_stats_handler(struct ctl_table *table, int write, 
	mutex_unlock(&bpf_stats_enabled_mutex);

	return ret;

}

#endif



static int bpf_unpriv_handler(struct ctl_table *table, int write,

			      void *buffer, size_t *lenp, loff_t *ppos)

{

	int ret, unpriv_enable = *(int *)table->data;

	bool locked_state = unpriv_enable == 1;

	struct ctl_table tmp = *table;



	if (write && !capable(CAP_SYS_ADMIN))

		return -EPERM;



	tmp.data = &unpriv_enable;

	ret = proc_dointvec_minmax(&tmp, write, buffer, lenp, ppos);

	if (write && !ret) {

		if (locked_state && unpriv_enable != 1)

			return -EPERM;

		*(int *)table->data = unpriv_enable;

	}

	return ret;

}

#endif /* CONFIG_BPF_SYSCALL && CONFIG_SYSCTL */



/*

 * /proc/sys support
@@ -2600,10 +2620,9 @@ static struct ctl_table kern_table[] = { 
		.data		= &sysctl_unprivileged_bpf_disabled,

		.maxlen		= sizeof(sysctl_unprivileged_bpf_disabled),

		.mode		= 0644,

		/* only handle a transition from default "0" to "1" */

		.proc_handler	= proc_dointvec_minmax,

		.extra1		= SYSCTL_ONE,

		.extra2		= SYSCTL_ONE,

		.proc_handler	= bpf_unpriv_handler,

		.extra1		= SYSCTL_ZERO,

		.extra2		= &two,

	},

	{

		.procname	= "bpf_stats_enabled",