bpf: Sysctl hook

Containerized applications may run as root and it may create problems
for whole host. Specifically such applications may change a sysctl and
affect applications in other containers.

Furthermore in existing infrastructure it may not be possible to just
completely disable writing to sysctl, instead such a process should be
gradual with ability to log what sysctl are being changed by a
container, investigate, limit the set of writable sysctl to currently
used ones (so that new ones can not be changed) and eventually reduce
this set to zero.

The patch introduces new program type BPF_PROG_TYPE_CGROUP_SYSCTL and
attach type BPF_CGROUP_SYSCTL to solve these problems on cgroup basis.

New program type has access to following minimal context:
	struct bpf_sysctl {
		__u32	write;
	};

Where @write indicates whether sysctl is being read (= 0) or written (=
1).

Helpers to access sysctl name and value will be introduced separately.

BPF_CGROUP_SYSCTL attach point is added to sysctl code right before
passing control to ctl_table->proc_handler so that BPF program can
either allow or deny access to sysctl.

Suggested-by: Roman Gushchin <guro@fb.com>
Signed-off-by: Andrey Ignatov <rdna@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 7 insertions, 0 deletions

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index d995eedfdd16..92c9b8a32b50 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -1888,6 +1888,9 @@ static int bpf_prog_attach(const union bpf_attr *attr)
         case BPF_FLOW_DISSECTOR:
                 ptype = BPF_PROG_TYPE_FLOW_DISSECTOR;
                 break;
+        case BPF_CGROUP_SYSCTL:
+                ptype = BPF_PROG_TYPE_CGROUP_SYSCTL;
+                break;
         default:
                 return -EINVAL;
         }
@@ -1966,6 +1969,9 @@ static int bpf_prog_detach(const union bpf_attr *attr)
                 return lirc_prog_detach(attr);
         case BPF_FLOW_DISSECTOR:
                 return skb_flow_dissector_bpf_prog_detach(attr);
+        case BPF_CGROUP_SYSCTL:
+                ptype = BPF_PROG_TYPE_CGROUP_SYSCTL;
+                break;
         default:
                 return -EINVAL;
         }
@@ -1999,6 +2005,7 @@ static int bpf_prog_query(const union bpf_attr *attr,
         case BPF_CGROUP_UDP6_SENDMSG:
         case BPF_CGROUP_SOCK_OPS:
         case BPF_CGROUP_DEVICE:
+        case BPF_CGROUP_SYSCTL:
                 break;
         case BPF_LIRC_MODE2:
                 return lirc_prog_query(attr, uattr);