bpf: wait for running BPF programs when updating map-in-map (1ae80cf3) · Commits · 戴 / test

The map-in-map frequently serves as a mechanism for atomic snapshotting of state that a BPF program might record. The current implementation is dangerous to use in this way, however, since userspace has no way of knowing when all programs that might have retrieved the "old" value of the map may have completed. This change ensures that map update operations on map-in-map map types always wait for all references to the old map to drop before returning to userspace. Signed-off-by:

Daniel Colascione <dancol@google.com> Reviewed-by:

Joel Fernandes (Google) <joel@joelfernandes.org> Signed-off-by:

Alexei Starovoitov <ast@kernel.org>

kernel/bpf/syscall.c

+13 −0

Original line number	Diff line number	Diff line
		@@ -748,6 +748,17 @@ err_put:
		return err;
		}

		static void maybe_wait_bpf_programs(struct bpf_map *map)
		{
		/* Wait for any running BPF programs to complete so that
		* userspace, when we return to it, knows that all programs
		* that could be running use the new map value.
		*/
		if (map->map_type == BPF_MAP_TYPE_HASH_OF_MAPS \|\|
		map->map_type == BPF_MAP_TYPE_ARRAY_OF_MAPS)
		synchronize_rcu();
		}

		#define BPF_MAP_UPDATE_ELEM_LAST_FIELD flags

		static int map_update_elem(union bpf_attr *attr)
		@@ -842,6 +853,7 @@ static int map_update_elem(union bpf_attr *attr)
		}
		__this_cpu_dec(bpf_prog_active);
		preempt_enable();
		maybe_wait_bpf_programs(map);
		out:
		free_value:
		kfree(value);
		@@ -894,6 +906,7 @@ static int map_delete_elem(union bpf_attr *attr)
		rcu_read_unlock();
		__this_cpu_dec(bpf_prog_active);
		preempt_enable();
		maybe_wait_bpf_programs(map);
		out:
		kfree(key);
		err_put:

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