If the cgroup associated with the receiving socket has an eBPF
programs installed, run them from sk_filter_trim_cap().

eBPF programs used in this context are expected to either return 1 to
let the packet pass, or != 1 to drop them. The programs have access to
the skb through bpf_skb_load_bytes(), and the payload starts at the
network headers (L3).

Note that cgroup_bpf_run_filter() is stubbed out as static inline nop
for !CONFIG_CGROUP_BPF, and is otherwise guarded by a static key if
the feature is unused.

Signed-off-by: Daniel Mack <dan...@zonque.org>
 net/core/filter.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/core/filter.c b/net/core/filter.c
index e46c98e..ce6e527 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -78,6 +78,10 @@ int sk_filter_trim_cap(struct sock *sk, struct sk_buff *skb, 
unsigned int cap)
        if (skb_pfmemalloc(skb) && !sock_flag(sk, SOCK_MEMALLOC))
                return -ENOMEM;
+       err = cgroup_bpf_run_filter(sk, skb, BPF_CGROUP_INET_INGRESS);
+       if (err)
+               return err;
        err = security_sock_rcv_skb(sk, skb);
        if (err)
                return err;

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