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Message-ID: <CAPhsuW4YQxoQxNXLw2APWN3JmLav1t==yB4upimUvHN5ZKMKRA@mail.gmail.com>
Date: Sun, 2 Dec 2018 23:48:10 -0800
From: Song Liu <liu.song.a23@...il.com>
To: Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc: Networking <netdev@...r.kernel.org>,
Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Petar Penkov <peterpenkov96@...il.com>, vladum@...gle.com,
Petar Penkov <ppenkov@...gle.com>,
Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH bpf-next v2] bpf: allow BPF read access to qdisc pkt_len
On Sun, Dec 2, 2018 at 5:18 PM Willem de Bruijn
<willemdebruijn.kernel@...il.com> wrote:
>
> From: Petar Penkov <ppenkov@...gle.com>
>
> The pkt_len field in qdisc_skb_cb stores the skb length as it will
> appear on the wire after segmentation. For byte accounting, this value
> is more accurate than skb->len. It is computed on entry to the TC
> layer, so only valid there.
>
> Allow read access to this field from BPF tc classifier and action
> programs. The implementation is analogous to tc_classid, aside from
> restricting to read access.
>
> To distinguish it from skb->len and self-describe export as wire_len.
>
> Changes v1->v2
> - Rename pkt_len to wire_len
>
> Signed-off-by: Petar Penkov <ppenkov@...gle.com>
> Signed-off-by: Vlad Dumitrescu <vladum@...gle.com>
> Signed-off-by: Willem de Bruijn <willemb@...gle.com>
Acked-by: Song Liu <songliubraving@...com>
> ---
> include/uapi/linux/bpf.h | 1 +
> net/core/filter.c | 16 +++++++++++
> tools/include/uapi/linux/bpf.h | 1 +
> tools/testing/selftests/bpf/test_verifier.c | 32 +++++++++++++++++++++
> 4 files changed, 50 insertions(+)
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 8050caea7495..0183b8e70a9e 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -2497,6 +2497,7 @@ struct __sk_buff {
> __u32 data_meta;
> struct bpf_flow_keys *flow_keys;
> __u64 tstamp;
> + __u32 wire_len;
> };
>
> struct bpf_tunnel_key {
> diff --git a/net/core/filter.c b/net/core/filter.c
> index bd0df75dc7b6..3d54af4c363d 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -5773,6 +5773,7 @@ static bool sk_filter_is_valid_access(int off, int size,
> case bpf_ctx_range(struct __sk_buff, flow_keys):
> case bpf_ctx_range_till(struct __sk_buff, family, local_port):
> case bpf_ctx_range(struct __sk_buff, tstamp):
> + case bpf_ctx_range(struct __sk_buff, wire_len):
> return false;
> }
>
> @@ -5797,6 +5798,7 @@ static bool cg_skb_is_valid_access(int off, int size,
> case bpf_ctx_range(struct __sk_buff, tc_classid):
> case bpf_ctx_range(struct __sk_buff, data_meta):
> case bpf_ctx_range(struct __sk_buff, flow_keys):
> + case bpf_ctx_range(struct __sk_buff, wire_len):
> return false;
> case bpf_ctx_range(struct __sk_buff, data):
> case bpf_ctx_range(struct __sk_buff, data_end):
> @@ -5843,6 +5845,7 @@ static bool lwt_is_valid_access(int off, int size,
> case bpf_ctx_range(struct __sk_buff, data_meta):
> case bpf_ctx_range(struct __sk_buff, flow_keys):
> case bpf_ctx_range(struct __sk_buff, tstamp):
> + case bpf_ctx_range(struct __sk_buff, wire_len):
> return false;
> }
>
> @@ -6273,6 +6276,7 @@ static bool sk_skb_is_valid_access(int off, int size,
> case bpf_ctx_range(struct __sk_buff, data_meta):
> case bpf_ctx_range(struct __sk_buff, flow_keys):
> case bpf_ctx_range(struct __sk_buff, tstamp):
> + case bpf_ctx_range(struct __sk_buff, wire_len):
> return false;
> }
>
> @@ -6360,6 +6364,7 @@ static bool flow_dissector_is_valid_access(int off, int size,
> case bpf_ctx_range(struct __sk_buff, data_meta):
> case bpf_ctx_range_till(struct __sk_buff, family, local_port):
> case bpf_ctx_range(struct __sk_buff, tstamp):
> + case bpf_ctx_range(struct __sk_buff, wire_len):
> return false;
> }
>
> @@ -6685,6 +6690,17 @@ static u32 bpf_convert_ctx_access(enum bpf_access_type type,
> bpf_target_off(struct sk_buff,
> tstamp, 8,
> target_size));
> + break;
> +
> + case offsetof(struct __sk_buff, wire_len):
> + BUILD_BUG_ON(FIELD_SIZEOF(struct qdisc_skb_cb, pkt_len) != 4);
> +
> + off = si->off;
> + off -= offsetof(struct __sk_buff, wire_len);
> + off += offsetof(struct sk_buff, cb);
> + off += offsetof(struct qdisc_skb_cb, pkt_len);
> + *target_size = 4;
> + *insn++ = BPF_LDX_MEM(BPF_W, si->dst_reg, si->src_reg, off);
> }
>
> return insn - insn_buf;
> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> index 8050caea7495..0183b8e70a9e 100644
> --- a/tools/include/uapi/linux/bpf.h
> +++ b/tools/include/uapi/linux/bpf.h
> @@ -2497,6 +2497,7 @@ struct __sk_buff {
> __u32 data_meta;
> struct bpf_flow_keys *flow_keys;
> __u64 tstamp;
> + __u32 wire_len;
> };
>
> struct bpf_tunnel_key {
> diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c
> index c3b038f26ece..b4b4a3f93639 100644
> --- a/tools/testing/selftests/bpf/test_verifier.c
> +++ b/tools/testing/selftests/bpf/test_verifier.c
> @@ -14033,6 +14033,38 @@ static struct bpf_test tests[] = {
> .result_unpriv = REJECT,
> .result = ACCEPT,
> },
> + {
> + "check wire_len is not readable by sockets",
> + .insns = {
> + BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1,
> + offsetof(struct __sk_buff, wire_len)),
> + BPF_EXIT_INSN(),
> + },
> + .errstr = "invalid bpf_context access",
> + .result = REJECT,
> + },
> + {
> + "check wire_len is readable by tc classifier",
> + .insns = {
> + BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1,
> + offsetof(struct __sk_buff, wire_len)),
> + BPF_EXIT_INSN(),
> + },
> + .prog_type = BPF_PROG_TYPE_SCHED_CLS,
> + .result = ACCEPT,
> + },
> + {
> + "check wire_len is not writable by tc classifier",
> + .insns = {
> + BPF_STX_MEM(BPF_W, BPF_REG_1, BPF_REG_1,
> + offsetof(struct __sk_buff, wire_len)),
> + BPF_EXIT_INSN(),
> + },
> + .prog_type = BPF_PROG_TYPE_SCHED_CLS,
> + .errstr = "invalid bpf_context access",
> + .errstr_unpriv = "R1 leaks addr",
> + .result = REJECT,
> + },
> };
>
> static int probe_filter_length(const struct bpf_insn *fp)
> --
> 2.20.0.rc1.387.gf8505762e3-goog
>
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