> On Jan 28, 2019, at 6:43 PM, Alexei Starovoitov <a...@kernel.org> wrote:
>
> Disabled preemption is necessary for proper access to per-cpu maps
> from BPF programs.
>
> But the sender side of socket filters didn't have preemption disabled:
> unix_dgram_sendmsg->sk_filter->sk_filter_trim_cap->bpf_prog_run_save_cb->BPF_PROG_RUN
>
> and a combination of af_packet with tun device didn't disable either:
> tpacket_snd->packet_direct_xmit->packet_pick_tx_queue->ndo_select_queue->
> tun_select_queue->tun_ebpf_select_queue->bpf_prog_run_clear_cb->BPF_PROG_RUN
>
> Disable preemption before executing BPF programs (both classic and extended).
>
> Reported-by: Jann Horn <ja...@google.com>
> Signed-off-by: Alexei Starovoitov <a...@kernel.org>
Acked-by: Song Liu <songliubrav...@fb.com>
> ---
> include/linux/filter.h | 21 ++++++++++++++++++---
> kernel/bpf/cgroup.c | 2 +-
> 2 files changed, 19 insertions(+), 4 deletions(-)
>
> diff --git a/include/linux/filter.h b/include/linux/filter.h
> index ad106d845b22..e532fcc6e4b5 100644
> --- a/include/linux/filter.h
> +++ b/include/linux/filter.h
> @@ -591,8 +591,8 @@ static inline u8 *bpf_skb_cb(struct sk_buff *skb)
> return qdisc_skb_cb(skb)->data;
> }
>
> -static inline u32 bpf_prog_run_save_cb(const struct bpf_prog *prog,
> - struct sk_buff *skb)
> +static inline u32 __bpf_prog_run_save_cb(const struct bpf_prog *prog,
> + struct sk_buff *skb)
> {
> u8 *cb_data = bpf_skb_cb(skb);
> u8 cb_saved[BPF_SKB_CB_LEN];
> @@ -611,15 +611,30 @@ static inline u32 bpf_prog_run_save_cb(const struct
> bpf_prog *prog,
> return res;
> }
>
> +static inline u32 bpf_prog_run_save_cb(const struct bpf_prog *prog,
> + struct sk_buff *skb)
> +{
> + u32 res;
> +
> + preempt_disable();
> + res = __bpf_prog_run_save_cb(prog, skb);
> + preempt_enable();
> + return res;
> +}
> +
> static inline u32 bpf_prog_run_clear_cb(const struct bpf_prog *prog,
> struct sk_buff *skb)
> {
> u8 *cb_data = bpf_skb_cb(skb);
> + u32 res;
>
> if (unlikely(prog->cb_access))
> memset(cb_data, 0, BPF_SKB_CB_LEN);
>
> - return BPF_PROG_RUN(prog, skb);
> + preempt_disable();
> + res = BPF_PROG_RUN(prog, skb);
> + preempt_enable();
> + return res;
> }
>
> static __always_inline u32 bpf_prog_run_xdp(const struct bpf_prog *prog,
> diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
> index ab612fe9862f..d17d05570a3f 100644
> --- a/kernel/bpf/cgroup.c
> +++ b/kernel/bpf/cgroup.c
> @@ -572,7 +572,7 @@ int __cgroup_bpf_run_filter_skb(struct sock *sk,
> bpf_compute_and_save_data_end(skb, &saved_data_end);
>
> ret = BPF_PROG_RUN_ARRAY(cgrp->bpf.effective[type], skb,
> - bpf_prog_run_save_cb);
> + __bpf_prog_run_save_cb);
> bpf_restore_data_end(skb, saved_data_end);
> __skb_pull(skb, offset);
> skb->sk = save_sk;
> --
> 2.20.0
>
