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authorDaniel Borkmann <daniel@iogearbox.net>2021-05-11 22:35:17 +0200
committerAlexei Starovoitov <ast@kernel.org>2021-05-11 13:56:16 -0700
commit08389d888287c3823f80b0216766b71e17f0aba5 (patch)
tree6d5c9fc6185c944141c44c00dcafa22901156908
parentb24abcff918a5cbf44b0c982bd3477a93e8e4911 (diff)
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: 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
-rw-r--r--Documentation/admin-guide/sysctl/kernel.rst17
-rw-r--r--kernel/bpf/Kconfig10
-rw-r--r--kernel/bpf/syscall.c3
-rw-r--r--kernel/sysctl.c29
4 files changed, 50 insertions, 9 deletions
diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
index 1d56a6b73a4e..24ab20d7a50a 100644
--- a/Documentation/admin-guide/sysctl/kernel.rst
+++ b/Documentation/admin-guide/sysctl/kernel.rst
@@ -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
========
diff --git a/kernel/bpf/Kconfig b/kernel/bpf/Kconfig
index b4edaefc6255..26b591e23f16 100644
--- a/kernel/bpf/Kconfig
+++ b/kernel/bpf/Kconfig
@@ -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
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 941ca06d9dfa..ea04b0deb5ce 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -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)
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index f91d327273c1..6df7c81f7cdd 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -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",