UPSTREAM: bpf: Add kconfig knob for disabling unpriv bpf by default

commit 08389d888287c3823f80b0216766b71e17f0aba5 upstream.

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.

Bug: 215557547
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/74ec548079189e4e4dffaeb42b8987bb3c852eee.1620765074.git.daniel@iogearbox.net
[fllinden@amazon.com: backported to 5.4]
Signed-off-by: Frank van der Linden <fllinden@amazon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit c230f6ba10)
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: I6d80853f0bd2c8618d956d967681c97b931a6137
This commit is contained in:
Daniel Borkmann 2021-05-11 22:35:17 +02:00 committed by Greg Kroah-Hartman
parent 2aea7dc18f
commit 508711cf30
4 changed files with 58 additions and 5 deletions

View File

@ -1125,6 +1125,27 @@ NMI switch that most IA32 servers have fires unknown NMI up, for
example. If a system hangs up, try pressing the NMI switch.
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 set to 1, this can't be cleared from the running kernel
anymore.
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:
=========

View File

@ -1626,6 +1626,16 @@ config BPF_JIT_ALWAYS_ON
Enables BPF JIT and removes BPF interpreter to avoid
speculative execution of BPF instructions by the interpreter
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).
config USERFAULTFD
bool "Enable userfaultfd() system call"
depends on MMU

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@ -39,7 +39,8 @@ static DEFINE_SPINLOCK(prog_idr_lock);
static DEFINE_IDR(map_idr);
static DEFINE_SPINLOCK(map_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, _ops)

View File

@ -251,6 +251,28 @@ static int sysrq_sysctl_handler(struct ctl_table *table, int write,
#endif
#ifdef CONFIG_BPF_SYSCALL
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
static struct ctl_table kern_table[];
static struct ctl_table vm_table[];
static struct ctl_table fs_table[];
@ -1256,10 +1278,9 @@ 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",