Re: [bpf PATCH] bpf: sockmap missing NULL psock check
From: Daniel Borkmann <daniel@iogearbox.net>
Date: 2018-01-04 11:21:57
On 01/03/2018 04:47 AM, John Fastabend wrote:
quoted hunk ↗ jump to hunk
Add psock NULL check to handle a racing sock event that can get the sk_callback_lock before this case but after xchg happens causing the refcnt to hit zero and sock user data (psock) to be null and queued for garbage collection. Also add a comment in the code because this is a bit subtle and not obvious in my opinion. Signed-off-by: John Fastabend <john.fastabend@gmail.com> --- kernel/bpf/sockmap.c | 7 +++++++ 1 file changed, 7 insertions(+)diff --git a/kernel/bpf/sockmap.c b/kernel/bpf/sockmap.c index 5ee2e41..dfbbde2 100644 --- a/kernel/bpf/sockmap.c +++ b/kernel/bpf/sockmap.c@@ -591,6 +591,13 @@ static void sock_map_free(struct bpf_map *map) write_lock_bh(&sock->sk_callback_lock); psock = smap_psock_sk(sock); + /* This check handles a racing sock event that can get the + * sk_callback_lock before this case but after xchg happens + * causing the refcnt to hit zero and sock user data (psock) + * to be null and queued for garbage collection. + */ + if (unlikely(!psock)) + continue;
Don't we need a write_unlock_bh(&sock->sk_callback_lock) before the continue?
smap_list_remove(psock, &stab->sock_map[i]); smap_release_sock(psock, sock); write_unlock_bh(&sock->sk_callback_lock);