bpf: add bpf_skb_change_tail helper
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>
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 0f665cb..7047448 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -2295,7 +2295,7 @@
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 @@
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 @@
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 @@
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 @@
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)