From 4bea15f7933dc87a091a7481590dd2ea1088b2bf Mon Sep 17 00:00:00 2001 From: Daniel Colascione Date: Fri, 12 Oct 2018 03:54:27 -0700 Subject: [PATCH] bpf: wait for running BPF programs when updating map-in-map commit 1ae80cf31938c8f77c37a29bbe29e7f1cd492be8 upstream. 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 Reviewed-by: Joel Fernandes (Google) Signed-off-by: Alexei Starovoitov [fengc@google.com: 4.14 backport: adjust context] Signed-off-by: Chenbo Feng Signed-off-by: Greg Kroah-Hartman --- kernel/bpf/syscall.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c index ea22d0b6a9f0..5c9deed4524e 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c @@ -519,6 +519,17 @@ 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) @@ -592,6 +603,7 @@ static int map_update_elem(union bpf_attr *attr) } __this_cpu_dec(bpf_prog_active); preempt_enable(); + maybe_wait_bpf_programs(map); if (!err) trace_bpf_map_update_elem(map, ufd, key, value); @@ -636,6 +648,7 @@ 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); if (!err) trace_bpf_map_delete_elem(map, ufd, key); -- 2.34.1