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bpf: Add kconfig knob for disabling unpriv bpf by default

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commit 08389d8882 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.

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 4.9]
Signed-off-by: Frank van der Linden <fllinden@amazon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Daniel Borkmann
2021-05-11 22:35:17 +02:00
committed by Greg Kroah-Hartman
parent 32b0c05460
commit b6ef4bc38b
4 changed files with 58 additions and 5 deletions
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29
kernel/sysctl.c
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@@ -221,6 +221,28 @@ 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[];
@@ -1202,10 +1224,9 @@ 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 = &one,
.extra2 = &one,
.proc_handler = bpf_unpriv_handler,
.extra1 = &zero,
.extra2 = &two,
},
#endif
#if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU)