From 965931e3a803a506482616f89239eff6901c17b8 Mon Sep 17 00:00:00 2001 From: Yonghong Song Date: Tue, 14 Aug 2018 11:01:12 -0700 Subject: [PATCH] bpf: fix a rcu usage warning in bpf_prog_array_copy_core() Commit 394e40a29788 ("bpf: extend bpf_prog_array to store pointers to the cgroup storage") refactored the bpf_prog_array_copy_core() to accommodate new structure bpf_prog_array_item which contains bpf_prog array itself. In the old code, we had perf_event_query_prog_array(): mutex_lock(...) bpf_prog_array_copy_call(): prog = rcu_dereference_check(array, 1)->progs bpf_prog_array_copy_core(prog, ...) mutex_unlock(...) With the above commit, we had perf_event_query_prog_array(): mutex_lock(...) bpf_prog_array_copy_call(): bpf_prog_array_copy_core(array, ...): item = rcu_dereference(array)->items; ... mutex_unlock(...) The new code will trigger a lockdep rcu checking warning. The fix is to change rcu_dereference() to rcu_dereference_check() to prevent such a warning. Reported-by: syzbot+6e72317008eef84a216b@syzkaller.appspotmail.com Fixes: 394e40a29788 ("bpf: extend bpf_prog_array to store pointers to the cgroup storage") Cc: Roman Gushchin Signed-off-by: Yonghong Song Acked-by: Alexei Starovoitov Acked-by: Roman Gushchin Signed-off-by: Daniel Borkmann --- kernel/bpf/core.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c index 4d09e610777f..3f5bf1af0826 100644 --- a/kernel/bpf/core.c +++ b/kernel/bpf/core.c @@ -1579,7 +1579,7 @@ static bool bpf_prog_array_copy_core(struct bpf_prog_array __rcu *array, struct bpf_prog_array_item *item; int i = 0; - item = rcu_dereference(array)->items; + item = rcu_dereference_check(array, 1)->items; for (; item->prog; item++) { if (item->prog == &dummy_bpf_prog.prog) continue;