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bpf: add bpf_skb_change_tail helper

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This work adds a bpf_skb_change_tail() helper for tc BPF programs. The
basic idea is to expand or shrink the skb in a controlled manner. The
eBPF program can then rewrite the rest via helpers like bpf_skb_store_bytes(),
bpf_lX_csum_replace() and others rather than passing a raw buffer for
writing here.

bpf_skb_change_tail() is really a slow path helper and intended for
replies with f.e. ICMP control messages. Concept is similar to other
helpers like bpf_skb_change_proto() helper to keep the helper without
protocol specifics and let the BPF program mangle the remaining parts.
A flags field has been added and is reserved for now should we extend
the helper in future.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Daniel Borkmann 2016-08-18 01:00:39 +02:00 • committed by David S. Miller
parent 45c7fffaf7
commit 5293efe62d
3 changed files with 150 additions and 4 deletions
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43
include/linux/skbuff.h
View file

@ -2295,7 +2295,7 @@ static inline int pskb_network_may_pull(struct sk_buff *skb, unsigned int len)
int ___pskb_trim(struct sk_buff *skb, unsigned int len);
static inline void __skb_trim(struct sk_buff *skb, unsigned int len)
static inline void __skb_set_length(struct sk_buff *skb, unsigned int len)
{
if (unlikely(skb_is_nonlinear(skb))) {
WARN_ON(1);
@ -2305,6 +2305,11 @@ static inline void __skb_trim(struct sk_buff *skb, unsigned int len)
skb_set_tail_pointer(skb, len);
}
static inline void __skb_trim(struct sk_buff *skb, unsigned int len)
{
__skb_set_length(skb, len);
}
void skb_trim(struct sk_buff *skb, unsigned int len);
static inline int __pskb_trim(struct sk_buff *skb, unsigned int len)
@ -2335,6 +2340,20 @@ static inline void pskb_trim_unique(struct sk_buff *skb, unsigned int len)
BUG_ON(err);
}
static inline int __skb_grow(struct sk_buff *skb, unsigned int len)
{
unsigned int diff = len - skb->len;
if (skb_tailroom(skb) < diff) {
int ret = pskb_expand_head(skb, 0, diff - skb_tailroom(skb),
GFP_ATOMIC);
if (ret)
return ret;
}
__skb_set_length(skb, len);
return 0;
}
/**
* skb_orphan - orphan a buffer
* @skb: buffer to orphan
@ -2938,6 +2957,21 @@ static inline int pskb_trim_rcsum(struct sk_buff *skb, unsigned int len)
return __pskb_trim(skb, len);
}
static inline int __skb_trim_rcsum(struct sk_buff *skb, unsigned int len)
{
if (skb->ip_summed == CHECKSUM_COMPLETE)
skb->ip_summed = CHECKSUM_NONE;
__skb_trim(skb, len);
return 0;
}
static inline int __skb_grow_rcsum(struct sk_buff *skb, unsigned int len)
{
if (skb->ip_summed == CHECKSUM_COMPLETE)
skb->ip_summed = CHECKSUM_NONE;
return __skb_grow(skb, len);
}
#define skb_queue_walk(queue, skb) \
for (skb = (queue)->next; \
skb != (struct sk_buff *)(queue); \
@ -3726,6 +3760,13 @@ static inline bool skb_is_gso_v6(const struct sk_buff *skb)
return skb_shinfo(skb)->gso_type & SKB_GSO_TCPV6;
}
static inline void skb_gso_reset(struct sk_buff *skb)
{
skb_shinfo(skb)->gso_size = 0;
skb_shinfo(skb)->gso_segs = 0;
skb_shinfo(skb)->gso_type = 0;
}
void __skb_warn_lro_forwarding(const struct sk_buff *skb);
static inline bool skb_warn_if_lro(const struct sk_buff *skb)