bpf: Fix missing prog untrack in release_maps

Commit da765a2f ("bpf: Add poke dependency tracking for prog array
maps") wrongly assumed that in case of prog load errors, we're cleaning
up all program tracking via bpf_free_used_maps().

However, it can happen that we're still at the point where we didn't copy
map pointers into the prog's aux section such that env->prog->aux->used_maps
is still zero, running into a UAF. In such case, the verifier has similar
release_maps() helper that drops references to used maps from its env.

Consolidate the release code into __bpf_free_used_maps() and call it from
all sides to fix it.

Fixes: da765a2f ("bpf: Add poke dependency tracking for prog array maps")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/1c2909484ca524ae9f55109b06f22b6213e76376.1576514756.git.daniel@iogearbox.net

include/linux/bpf.h

@@ -818,6 +818,8 @@ struct bpf_prog * __must_check bpf_prog_inc_not_zero(struct bpf_prog *prog);
 void bpf_prog_put(struct bpf_prog *prog);
 int __bpf_prog_charge(struct user_struct *user, u32 pages);
 void __bpf_prog_uncharge(struct user_struct *user, u32 pages);
+void __bpf_free_used_maps(struct bpf_prog_aux *aux,
+			  struct bpf_map **used_maps, u32 len);
 
 void bpf_prog_free_id(struct bpf_prog *prog, bool do_idr_lock);
 void bpf_map_free_id(struct bpf_map *map, bool do_idr_lock);

kernel/bpf/core.c

@@ -2048,18 +2048,24 @@ static void bpf_free_cgroup_storage(struct bpf_prog_aux *aux)
 	}
 }
 
-static void bpf_free_used_maps(struct bpf_prog_aux *aux)
+void __bpf_free_used_maps(struct bpf_prog_aux *aux,
+			  struct bpf_map **used_maps, u32 len)
 {
 	struct bpf_map *map;
-	int i;
+	u32 i;
 
 	bpf_free_cgroup_storage(aux);
-	for (i = 0; i < aux->used_map_cnt; i++) {
-		map = aux->used_maps[i];
+	for (i = 0; i < len; i++) {
+		map = used_maps[i];
 		if (map->ops->map_poke_untrack)
 			map->ops->map_poke_untrack(map, aux);
 		bpf_map_put(map);
 	}
+}
+
+static void bpf_free_used_maps(struct bpf_prog_aux *aux)
+{
+	__bpf_free_used_maps(aux, aux->used_maps, aux->used_map_cnt);
 	kfree(aux->used_maps);
 }
 

kernel/bpf/verifier.c

@@ -8298,18 +8298,8 @@ static int replace_map_fd_with_map_ptr(struct bpf_verifier_env *env)
 /* drop refcnt of maps used by the rejected program */
 static void release_maps(struct bpf_verifier_env *env)
 {
-	enum bpf_cgroup_storage_type stype;
-	int i;
-
-	for_each_cgroup_storage_type(stype) {
-		if (!env->prog->aux->cgroup_storage[stype])
-			continue;
-		bpf_cgroup_storage_release(env->prog,
-			env->prog->aux->cgroup_storage[stype]);
-	}
-
-	for (i = 0; i < env->used_map_cnt; i++)
-		bpf_map_put(env->used_maps[i]);
+	__bpf_free_used_maps(env->prog->aux, env->used_maps,
+			     env->used_map_cnt);
 }
 
 /* convert pseudo BPF_LD_IMM64 into generic BPF_LD_IMM64 */