Allow calling bpf_map_update_elem on sockmap and sockhash from a BPF
context. The synchronization required for this is a bit fiddly: we
need to prevent the socket from changing its state while we add it
to the sockmap, since we rely on getting a callback via
sk_prot->unhash. However, we can't just lock_sock like in
sock_map_sk_acquire because that might sleep. So instead we disable
softirq processing and use bh_lock_sock to prevent further
modification.
Signed-off-by: Lorenz Bauer <lmb@xxxxxxxxxxxxxx>
---
kernel/bpf/verifier.c | 41 +++++++++++++++++++++++++++++++++++++++--
net/core/sock_map.c | 24 ++++++++++++++++++++++++
2 files changed, 63 insertions(+), 2 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 24feec515d3e..7779057f57dc 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -4180,6 +4180,41 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
return -EACCES;
}
+static bool may_update_sockmap(struct bpf_verifier_env *env, int func_id)
+{
+ enum bpf_attach_type eatype = env->prog->expected_attach_type;
+ enum bpf_prog_type type = env->prog->type;
+
+ if (func_id != BPF_FUNC_map_update_elem)
+ return false;
+
+ /* It's not possible to get access to a locked struct sock in these
+ * contexts, so updating is safe.
+ */
+ switch (type) {
+ case BPF_PROG_TYPE_TRACING:
+ if (eatype == BPF_TRACE_ITER)
+ return true;
+ break;
+ case BPF_PROG_TYPE_SOCKET_FILTER:
+ case BPF_PROG_TYPE_SCHED_CLS:
+ case BPF_PROG_TYPE_SCHED_ACT:
+ case BPF_PROG_TYPE_XDP:
+ case BPF_PROG_TYPE_CGROUP_SKB:
+ case BPF_PROG_TYPE_SK_SKB:
+ case BPF_PROG_TYPE_SK_MSG:
+ case BPF_PROG_TYPE_SK_REUSEPORT:
+ case BPF_PROG_TYPE_FLOW_DISSECTOR:
+ case BPF_PROG_TYPE_SK_LOOKUP:
+ return true;
+ default:
+ break;
+ }
+
+ verbose(env, "cannot update sockmap in this context\n");
+ return false;
+}
+
static int check_map_func_compatibility(struct bpf_verifier_env *env,
struct bpf_map *map, int func_id)
{
@@ -4251,7 +4286,8 @@ static int check_map_func_compatibility(struct bpf_verifier_env *env,
func_id != BPF_FUNC_map_delete_elem &&
func_id != BPF_FUNC_msg_redirect_map &&
func_id != BPF_FUNC_sk_select_reuseport &&
- func_id != BPF_FUNC_map_lookup_elem)
+ func_id != BPF_FUNC_map_lookup_elem &&
+ !may_update_sockmap(env, func_id))
goto error;
break;
case BPF_MAP_TYPE_SOCKHASH:
@@ -4260,7 +4296,8 @@ static int check_map_func_compatibility(struct bpf_verifier_env *env,
func_id != BPF_FUNC_map_delete_elem &&
func_id != BPF_FUNC_msg_redirect_hash &&
func_id != BPF_FUNC_sk_select_reuseport &&
- func_id != BPF_FUNC_map_lookup_elem)
+ func_id != BPF_FUNC_map_lookup_elem &&
+ !may_update_sockmap(env, func_id))
goto error;
break;
case BPF_MAP_TYPE_REUSEPORT_SOCKARRAY:
diff --git a/net/core/sock_map.c b/net/core/sock_map.c
index 48e83f93ee66..d6c6e1e312fc 100644
--- a/net/core/sock_map.c
+++ b/net/core/sock_map.c
@@ -603,6 +603,28 @@ int sock_map_update_elem_sys(struct bpf_map *map, void *key, void *value,
return ret;
}
+static int sock_map_update_elem(struct bpf_map *map, void *key,
+ void *value, u64 flags)
+{
+ struct sock *sk = (struct sock *)value;
+ int ret;
+
+ if (!sock_map_sk_is_suitable(sk))
+ return -EOPNOTSUPP;
+
+ local_bh_disable();
+ bh_lock_sock(sk);
+ if (!sock_map_sk_state_allowed(sk))
+ ret = -EOPNOTSUPP;
+ else if (map->map_type == BPF_MAP_TYPE_SOCKMAP)
+ ret = sock_map_update_common(map, *(u32 *)key, sk, flags);
+ else
+ ret = sock_hash_update_common(map, key, sk, flags);
+ bh_unlock_sock(sk);
+ local_bh_enable();
+ return ret;
+}
+
BPF_CALL_4(bpf_sock_map_update, struct bpf_sock_ops_kern *, sops,
struct bpf_map *, map, void *, key, u64, flags)
{
@@ -687,6 +709,7 @@ const struct bpf_map_ops sock_map_ops = {
.map_free = sock_map_free,
.map_get_next_key = sock_map_get_next_key,
.map_lookup_elem_sys_only = sock_map_lookup_sys,
+ .map_update_elem = sock_map_update_elem,
.map_delete_elem = sock_map_delete_elem,
.map_lookup_elem = sock_map_lookup,
.map_release_uref = sock_map_release_progs,
@@ -1180,6 +1203,7 @@ const struct bpf_map_ops sock_hash_ops = {
.map_alloc = sock_hash_alloc,
.map_free = sock_hash_free,
.map_get_next_key = sock_hash_get_next_key,
+ .map_update_elem = sock_map_update_elem,
.map_delete_elem = sock_hash_delete_elem,
.map_lookup_elem = sock_hash_lookup,
.map_lookup_elem_sys_only = sock_hash_lookup_sys,
--
2.25.1
