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bpf: allow BPF read access to qdisc pkt_len

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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@google.com>
Signed-off-by: Vlad Dumitrescu <vladum@google.com>
Signed-off-by: Willem de Bruijn <willemb@google.com>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
This commit is contained in:
Petar Penkov
2018-12-02 20:18:19 -05:00
committed by Daniel Borkmann
parent de94b651ee
commit e3da08d057
4 changed files with 50 additions and 0 deletions
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32
tools/testing/selftests/bpf/test_verifier.c
View File

@@ -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)