From: Petar Penkov <ppen...@google.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.
Signed-off-by: Petar Penkov <ppen...@google.com>
Signed-off-by: Vlad Dumitrescu <vla...@google.com>
Signed-off-by: Willem de Bruijn <will...@google.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 597afdbc1ab9..ce028482d423 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -2483,6 +2483,7 @@ struct __sk_buff {
__u32 data_meta;
struct bpf_flow_keys *flow_keys;
__u64 tstamp;
+ __u32 pkt_len;
};
struct bpf_tunnel_key {
diff --git a/net/core/filter.c b/net/core/filter.c
index bd0df75dc7b6..af071ef22c0a 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, pkt_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, pkt_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, pkt_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, pkt_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, pkt_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, pkt_len):
+ BUILD_BUG_ON(FIELD_SIZEOF(struct qdisc_skb_cb, pkt_len) != 4);
+
+ off = si->off;
+ off -= offsetof(struct __sk_buff, pkt_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 597afdbc1ab9..ce028482d423 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -2483,6 +2483,7 @@ struct __sk_buff {
__u32 data_meta;
struct bpf_flow_keys *flow_keys;
__u64 tstamp;
+ __u32 pkt_len;
};
struct bpf_tunnel_key {
diff --git a/tools/testing/selftests/bpf/test_verifier.c
b/tools/testing/selftests/bpf/test_verifier.c
index 17021d2b6bfe..0ab37fb4afad 100644
--- a/tools/testing/selftests/bpf/test_verifier.c
+++ b/tools/testing/selftests/bpf/test_verifier.c
@@ -13972,6 +13972,38 @@ static struct bpf_test tests[] = {
.result_unpriv = REJECT,
.result = ACCEPT,
},
+ {
+ "check pkt_len is not readable by sockets",
+ .insns = {
+ BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1,
+ offsetof(struct __sk_buff, pkt_len)),
+ BPF_EXIT_INSN(),
+ },
+ .errstr = "invalid bpf_context access",
+ .result = REJECT,
+ },
+ {
+ "check pkt_len is readable by tc classifier",
+ .insns = {
+ BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1,
+ offsetof(struct __sk_buff, pkt_len)),
+ BPF_EXIT_INSN(),
+ },
+ .prog_type = BPF_PROG_TYPE_SCHED_CLS,
+ .result = ACCEPT,
+ },
+ {
+ "check pkt_len is not writable by tc classifier",
+ .insns = {
+ BPF_STX_MEM(BPF_W, BPF_REG_1, BPF_REG_1,
+ offsetof(struct __sk_buff, pkt_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
