From e3da08d057002f9d0831949d51666c3e15dc6b29 Mon Sep 17 00:00:00 2001 From: Petar Penkov Date: Sun, 2 Dec 2018 20:18:19 -0500 Subject: [PATCH] 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: Petar Penkov Signed-off-by: Vlad Dumitrescu Signed-off-by: Willem de Bruijn Acked-by: Song Liu Signed-off-by: Daniel Borkmann --- 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)