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selftests/bpf: use thoff instead of nhoff in BPF flow dissector
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We are returning thoff from the flow dissector, not the nhoff. Pass
thoff along with nhoff to the bpf program (initially thoff == nhoff)
and expect flow dissector amend/return thoff, not nhoff.

This avoids confusion, when by the time bpf flow dissector exits,
nhoff == thoff, which doesn't make much sense.

Signed-off-by: Stanislav Fomichev <sdf@google.com>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
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Stanislav Fomichev authored and Alexei Starovoitov committed Dec 7, 2018
1 parent 1b4e5ad commit 13e56ec
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Showing 2 changed files with 18 additions and 19 deletions.
1 change: 1 addition & 0 deletions net/core/flow_dissector.c
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Original file line number Diff line number Diff line change
Expand Up @@ -783,6 +783,7 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
/* Pass parameters to the BPF program */
cb->qdisc_cb.flow_keys = &flow_keys;
flow_keys.nhoff = nhoff;
flow_keys.thoff = nhoff;

bpf_compute_data_pointers((struct sk_buff *)skb);
result = BPF_PROG_RUN(attached, skb);
Expand Down
36 changes: 17 additions & 19 deletions tools/testing/selftests/bpf/bpf_flow.c
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Original file line number Diff line number Diff line change
Expand Up @@ -70,18 +70,18 @@ static __always_inline void *bpf_flow_dissect_get_header(struct __sk_buff *skb,
{
void *data_end = (void *)(long)skb->data_end;
void *data = (void *)(long)skb->data;
__u16 nhoff = skb->flow_keys->nhoff;
__u16 thoff = skb->flow_keys->thoff;
__u8 *hdr;

/* Verifies this variable offset does not overflow */
if (nhoff > (USHRT_MAX - hdr_size))
if (thoff > (USHRT_MAX - hdr_size))
return NULL;

hdr = data + nhoff;
hdr = data + thoff;
if (hdr + hdr_size <= data_end)
return hdr;

if (bpf_skb_load_bytes(skb, nhoff, buffer, hdr_size))
if (bpf_skb_load_bytes(skb, thoff, buffer, hdr_size))
return NULL;

return buffer;
Expand Down Expand Up @@ -158,13 +158,13 @@ static __always_inline int parse_ip_proto(struct __sk_buff *skb, __u8 proto)
/* Only inspect standard GRE packets with version 0 */
return BPF_OK;

keys->nhoff += sizeof(*gre); /* Step over GRE Flags and Proto */
keys->thoff += sizeof(*gre); /* Step over GRE Flags and Proto */
if (GRE_IS_CSUM(gre->flags))
keys->nhoff += 4; /* Step over chksum and Padding */
keys->thoff += 4; /* Step over chksum and Padding */
if (GRE_IS_KEY(gre->flags))
keys->nhoff += 4; /* Step over key */
keys->thoff += 4; /* Step over key */
if (GRE_IS_SEQ(gre->flags))
keys->nhoff += 4; /* Step over sequence number */
keys->thoff += 4; /* Step over sequence number */

keys->is_encap = true;

Expand All @@ -174,7 +174,7 @@ static __always_inline int parse_ip_proto(struct __sk_buff *skb, __u8 proto)
if (!eth)
return BPF_DROP;

keys->nhoff += sizeof(*eth);
keys->thoff += sizeof(*eth);

return parse_eth_proto(skb, eth->h_proto);
} else {
Expand All @@ -191,7 +191,6 @@ static __always_inline int parse_ip_proto(struct __sk_buff *skb, __u8 proto)
if ((__u8 *)tcp + (tcp->doff << 2) > data_end)
return BPF_DROP;

keys->thoff = keys->nhoff;
keys->sport = tcp->source;
keys->dport = tcp->dest;
return BPF_OK;
Expand All @@ -201,7 +200,6 @@ static __always_inline int parse_ip_proto(struct __sk_buff *skb, __u8 proto)
if (!udp)
return BPF_DROP;

keys->thoff = keys->nhoff;
keys->sport = udp->source;
keys->dport = udp->dest;
return BPF_OK;
Expand Down Expand Up @@ -252,8 +250,8 @@ PROG(IP)(struct __sk_buff *skb)
keys->ipv4_src = iph->saddr;
keys->ipv4_dst = iph->daddr;

keys->nhoff += iph->ihl << 2;
if (data + keys->nhoff > data_end)
keys->thoff += iph->ihl << 2;
if (data + keys->thoff > data_end)
return BPF_DROP;

if (iph->frag_off & bpf_htons(IP_MF | IP_OFFSET)) {
Expand Down Expand Up @@ -285,7 +283,7 @@ PROG(IPV6)(struct __sk_buff *skb)
keys->addr_proto = ETH_P_IPV6;
memcpy(&keys->ipv6_src, &ip6h->saddr, 2*sizeof(ip6h->saddr));

keys->nhoff += sizeof(struct ipv6hdr);
keys->thoff += sizeof(struct ipv6hdr);

return parse_ipv6_proto(skb, ip6h->nexthdr);
}
Expand All @@ -301,7 +299,7 @@ PROG(IPV6OP)(struct __sk_buff *skb)
/* hlen is in 8-octets and does not include the first 8 bytes
* of the header
*/
skb->flow_keys->nhoff += (1 + ip6h->hdrlen) << 3;
skb->flow_keys->thoff += (1 + ip6h->hdrlen) << 3;

return parse_ipv6_proto(skb, ip6h->nexthdr);
}
Expand All @@ -315,7 +313,7 @@ PROG(IPV6FR)(struct __sk_buff *skb)
if (!fragh)
return BPF_DROP;

keys->nhoff += sizeof(*fragh);
keys->thoff += sizeof(*fragh);
keys->is_frag = true;
if (!(fragh->frag_off & bpf_htons(IP6_OFFSET)))
keys->is_first_frag = true;
Expand All @@ -341,7 +339,7 @@ PROG(VLAN)(struct __sk_buff *skb)
__be16 proto;

/* Peek back to see if single or double-tagging */
if (bpf_skb_load_bytes(skb, keys->nhoff - sizeof(proto), &proto,
if (bpf_skb_load_bytes(skb, keys->thoff - sizeof(proto), &proto,
sizeof(proto)))
return BPF_DROP;

Expand All @@ -354,14 +352,14 @@ PROG(VLAN)(struct __sk_buff *skb)
if (vlan->h_vlan_encapsulated_proto != bpf_htons(ETH_P_8021Q))
return BPF_DROP;

keys->nhoff += sizeof(*vlan);
keys->thoff += sizeof(*vlan);
}

vlan = bpf_flow_dissect_get_header(skb, sizeof(*vlan), &_vlan);
if (!vlan)
return BPF_DROP;

keys->nhoff += sizeof(*vlan);
keys->thoff += sizeof(*vlan);
/* Only allow 8021AD + 8021Q double tagging and no triple tagging.*/
if (vlan->h_vlan_encapsulated_proto == bpf_htons(ETH_P_8021AD) ||
vlan->h_vlan_encapsulated_proto == bpf_htons(ETH_P_8021Q))
Expand Down

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