Re: [PATCH bpf-next v2] bpf: allow BPF read access to qdisc pkt_len

[Daniel Borkmann]

On 12/03/2018 02:18 AM, Willem de Bruijn wrote:
> From: Petar Penkov 
> 
> 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 
> Signed-off-by: Vlad Dumitrescu 
> Signed-off-by: Willem de Bruijn 

Applied to bpf-next, thanks!

Re: [PATCH bpf-next v2] bpf: allow BPF read access to qdisc pkt_len

[Song Liu]

On Sun, Dec 2, 2018 at 5:18 PM Willem de Bruijn
 wrote:
>
> From: Petar Penkov 
>
> 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 
> Signed-off-by: Vlad Dumitrescu 
> Signed-off-by: Willem de Bruijn 
Acked-by: Song Liu 

> ---
>  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
> @@ 

[PATCH bpf-next v2] bpf: allow BPF read access to qdisc pkt_len

[Willem de Bruijn]

From: Petar Penkov 

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 
Signed-off-by: Vlad Dumitrescu 
Signed-off-by: Willem de Bruijn 
---
 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,