[RFC PATCH 10/16] bpf/crib: Add struct sk_buff related CRIB kfuncs

[Juntong Deng <juntong.deng@xxxxxxxxxxx>]

This patch adds struct sk_buff related CRIB kfuncs.

bpf_skb_peek_tail() is used to get a pointer to the skb at the tail of
the socket queue.

bpf_cal_skb_size() is used to calculate the overall size of the skb data
(starting from the head).

bpf_skb_acquire()/bpf_skb_release() are used to acquire/release
references on struct sk_buff.

Signed-off-by: Juntong Deng <juntong.deng@xxxxxxxxxxx>
---
 kernel/bpf/crib/bpf_checkpoint.c | 14 +++++++++
 kernel/bpf/crib/bpf_crib.c       | 50 ++++++++++++++++++++++++++++++++
 2 files changed, 64 insertions(+)

diff --git a/kernel/bpf/crib/bpf_checkpoint.c b/kernel/bpf/crib/bpf_checkpoint.c
index 4d48f08324ef..d8cd4a1b73dc 100644
--- a/kernel/bpf/crib/bpf_checkpoint.c
+++ b/kernel/bpf/crib/bpf_checkpoint.c
@@ -10,6 +10,7 @@
 #include <linux/fdtable.h>
 #include <net/inet_common.h>
 #include <net/ipv6.h>
+#include <linux/skbuff.h>
 
 extern void bpf_file_release(struct file *file);
 
@@ -148,4 +149,17 @@ __bpf_kfunc int bpf_inet6_dst_addr_from_socket(struct socket *sock, struct socka
 	return inet6_getname(sock, (struct sockaddr *)addr, 1);
 }
 
+/**
+ * bpf_cal_skb_size() - Calculate the overall size of the data of specified skb
+ * (starting from the head)
+ *
+ * @skb: specified skb
+ *
+ * @returns the overall size of the data
+ */
+__bpf_kfunc int bpf_cal_skb_size(struct sk_buff *skb)
+{
+	return skb_end_offset(skb) + skb->data_len;
+}
+
 __bpf_kfunc_end_defs();
diff --git a/kernel/bpf/crib/bpf_crib.c b/kernel/bpf/crib/bpf_crib.c
index e33fa37f8f72..21889efa620c 100644
--- a/kernel/bpf/crib/bpf_crib.c
+++ b/kernel/bpf/crib/bpf_crib.c
@@ -13,6 +13,8 @@
 #include <linux/net.h>
 #include <linux/udp.h>
 #include <linux/tcp.h>
+#include <linux/skbuff.h>
+#include <linux/spinlock.h>
 
 __bpf_kfunc_start_defs();
 
@@ -209,6 +211,49 @@ __bpf_kfunc struct sk_buff_head *bpf_reader_queue_from_udp_sock(struct udp_sock
 	return &up->reader_queue;
 }
 
+/**
+ * bpf_skb_acquire() - Acquire a reference to struct sk_buff
+ *
+ * @skb: struct sk_buff that needs to acquire a reference
+ *
+ * @returns struct sk_buff that has acquired the reference
+ */
+__bpf_kfunc struct sk_buff *bpf_skb_acquire(struct sk_buff *skb)
+{
+	return skb_get(skb);
+}
+
+/**
+ * bpf_skb_release() - Release the reference acquired on struct sk_buff
+ *
+ * @skb: struct sk_buff that has acquired the reference
+ */
+__bpf_kfunc void bpf_skb_release(struct sk_buff *skb)
+{
+	consume_skb(skb);
+}
+
+/**
+ * bpf_skb_peek_tail() - peek at the tail of socket queue (sk_buff_head)
+ *
+ * Note that this function acquires a reference to struct sk_buff.
+ *
+ * @head: socket queue
+ *
+ * @returns pointer to the tail skb (sk_buff)
+ */
+__bpf_kfunc struct sk_buff *bpf_skb_peek_tail(struct sk_buff_head *head)
+{
+	struct sk_buff *skb;
+	unsigned long flags;
+
+	spin_lock_irqsave(&head->lock, flags);
+	skb = skb_peek_tail(head);
+	spin_unlock_irqrestore(&head->lock, flags);
+
+	return bpf_skb_acquire(skb);
+}
+
 __bpf_kfunc_end_defs();
 
 BTF_KFUNCS_START(bpf_crib_kfuncs)
@@ -239,6 +284,11 @@ BTF_ID_FLAGS(func, bpf_inet_dst_addr_from_socket, KF_TRUSTED_ARGS)
 BTF_ID_FLAGS(func, bpf_inet6_src_addr_from_socket, KF_TRUSTED_ARGS)
 BTF_ID_FLAGS(func, bpf_inet6_dst_addr_from_socket, KF_TRUSTED_ARGS)
 
+BTF_ID_FLAGS(func, bpf_skb_acquire, KF_ACQUIRE | KF_TRUSTED_ARGS)
+BTF_ID_FLAGS(func, bpf_skb_release, KF_RELEASE)
+BTF_ID_FLAGS(func, bpf_cal_skb_size, KF_TRUSTED_ARGS)
+BTF_ID_FLAGS(func, bpf_skb_peek_tail, KF_ACQUIRE | KF_TRUSTED_ARGS | KF_RET_NULL)
+
 BTF_KFUNCS_END(bpf_crib_kfuncs)
 
 static int bpf_prog_run_crib(struct bpf_prog *prog,
-- 
2.39.2