Re: [PATCH 2/3] security: bpf: Add eBPF LSM hooks and security field to eBPF map
From: Alexei Starovoitov <hidden>
Date: 2017-09-01 02:05:25
Also in:
linux-security-module, selinux
On Thu, Aug 31, 2017 at 01:56:34PM -0700, Chenbo Feng wrote:
From: Chenbo Feng <redacted> Introduce a pointer into struct bpf_map to hold the security information about the map. The actual security struct varies based on the security models implemented. Place the LSM hooks before each of the unrestricted eBPF operations, the map_update_elem and map_delete_elem operations are checked by security_map_modify. The map_lookup_elem and map_get_next_key operations are checked by securtiy_map_read. Signed-off-by: Chenbo Feng <redacted>
...
quoted hunk ↗ jump to hunk
@@ -410,6 +418,10 @@ static int map_lookup_elem(union bpf_attr *attr) if (IS_ERR(map)) return PTR_ERR(map); + err = security_map_read(map); + if (err) + return -EACCES; + key = memdup_user(ukey, map->key_size); if (IS_ERR(key)) { err = PTR_ERR(key);@@ -490,6 +502,10 @@ static int map_update_elem(union bpf_attr *attr) if (IS_ERR(map)) return PTR_ERR(map); + err = security_map_modify(map);
I don't feel these extra hooks are really thought through. With such hook you'll disallow map_update for given map. That's it. The key/values etc won't be used in such security decision. In such case you don't need such hooks in update/lookup at all. Only in map_creation and object_get calls where FD can be received. In other words I suggest to follow standard unix practices: Do permissions checks in open() and allow read/write() if FD is valid. Same here. Do permission checks in prog_load/map_create/obj_pin/get and that will be enough to jail bpf subsystem. bpf cmds that need to be fast (like lookup and update) should not have security hooks.