[PATCH 4.9 046/103] bpf: restrict access to core bpf sysctls

Greg Kroah-Hartman
2019-08-22T17:41:00Z

From: Daniel Borkmann <daniel@iogearbox.net>

commit 2e4a30983b0f9b19b59e38bbf7427d7fdd480d98 upstream.

Given BPF reaches far beyond just networking these days, it was
never intended to allow setting and in some cases reading those
knobs out of a user namespace root running without CAP_SYS_ADMIN,
thus tighten such access.

Also the bpf_jit_enable = 2 debugging mode should only be allowed
if kptr_restrict is not set since it otherwise can leak addresses
to the kernel log. Dump a note to the kernel log that this is for
debugging JITs only when enabled.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
[bwh: Backported to 4.9:
- We don't have bpf_dump_raw_ok(), so drop the condition based on it. This
condition only made it a bit harder for a privileged user to do something
silly.
- Drop change to bpf_jit_kallsyms]
Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/core/sysctl_net_core.c | 39 +++++++++++++++++++++++++++++++++++++--
1 file changed, 37 insertions(+), 2 deletions(-)

--- a/net/core/sysctl_net_core.c
+++ b/net/core/sysctl_net_core.c
@@ -232,6 +232,41 @@ static int proc_do_rss_key(struct ctl_ta
return proc_dostring(&fake_table, write, buffer, lenp, ppos);
}

+#ifdef CONFIG_BPF_JIT
+static int proc_dointvec_minmax_bpf_enable(struct ctl_table *table, int write,
+ void __user *buffer, size_t *lenp,
+ loff_t *ppos)
+{
+ int ret, jit_enable = *(int *)table->data;
+ struct ctl_table tmp = *table;
+
+ if (write && !capable(CAP_SYS_ADMIN))
+ return -EPERM;
+
+ tmp.data = &jit_enable;
+ ret = proc_dointvec_minmax(&tmp, write, buffer, lenp, ppos);
+ if (write && !ret) {
+ *(int *)table->data = jit_enable;
+ if (jit_enable == 2)
+ pr_warn("bpf_jit_enable = 2 was set! NEVER use this in production, only for JIT debugging!\n");
+ }
+ return ret;
+}
+
+# ifdef CONFIG_HAVE_EBPF_JIT
+static int
+proc_dointvec_minmax_bpf_restricted(struct ctl_table *table, int write,
+ void __user *buffer, size_t *lenp,
+ loff_t *ppos)
+{
+ if (!capable(CAP_SYS_ADMIN))
+ return -EPERM;
+
+ return proc_dointvec_minmax(table, write, buffer, lenp, ppos);
+}
+# endif
+#endif
+
static struct ctl_table net_core_table[] = {
#ifdef CONFIG_NET
{
@@ -293,7 +328,7 @@ static struct ctl_table net_core_table[]
.data = &bpf_jit_enable,
.maxlen = sizeof(int),
.mode = 0644,
- .proc_handler = proc_dointvec_minmax,
+ .proc_handler = proc_dointvec_minmax_bpf_enable,
# ifdef CONFIG_BPF_JIT_ALWAYS_ON
.extra1 = &one,
.extra2 = &one,
@@ -308,7 +343,7 @@ static struct ctl_table net_core_table[]
.data = &bpf_jit_harden,
.maxlen = sizeof(int),
.mode = 0600,
- .proc_handler = proc_dointvec_minmax,
+ .proc_handler = proc_dointvec_minmax_bpf_restricted,
.extra1 = &zero,
.extra2 = &two,
},