Commit e3da08d0 authored by Petar Penkov's avatar Petar Penkov Committed by Daniel Borkmann
Browse files

bpf: allow BPF read access to qdisc pkt_len 



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: default avatarPetar Penkov <ppenkov@google.com>
Signed-off-by: default avatarVlad Dumitrescu <vladum@google.com>
Signed-off-by: default avatarWillem de Bruijn <willemb@google.com>
Acked-by: default avatarSong Liu <songliubraving@fb.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
parent de94b651

include/uapi/linux/bpf.h

+1 −0
Original line number Diff line number Diff line
@@ -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 {

net/core/filter.c

+16 −0
Original line number Diff line number Diff line
@@ -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;

tools/include/uapi/linux/bpf.h

+1 −0
Original line number Diff line number Diff line
@@ -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 {

tools/testing/selftests/bpf/test_verifier.c

+32 −0
Original line number Diff line number Diff line
@@ -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)

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