On 6/21/23 20:37, Yonghong Song wrote:
On 6/20/23 10:14 AM, Kui-Feng Lee wrote:
Always call BPF filters if CGROUP BPF is enabled for EGRESS without
checking skb->sk against sk.
The filters were called only if skb is owned by the sock that the
skb is sent out through. In another words, skb->sk should point to
the sock that it is sending through its egress. However, the filters
would
miss SYNACK skbs that they are owned by a request_sock but sent through
the listening sock, that is the socket listening incoming connections.
This is an unnecessary restrict.
The original patch which introduced 'sk == skb->sk' is
3007098494be cgroup: add support for eBPF programs
There are no mentioning in commit message why 'sk == skb->sk'
is needed. So it is possible that this is just restricted
for use cases at that moment. Now there are use cases
where 'sk != skb->sk' so removing this check can enable
the new use case. Maybe you can add this into your commit
message so people can understand the history of 'sk == skb->sk'.
After checking the code and the Alexei's comment[1] again, this check
may be different from what I thought. In another post[2],
Daniel Borkmann mentioned
Wouldn't that mean however, when you go through stacked devices that
you'd run the same eBPF cgroup program for skb->sk multiple times?
I read this paragraph several times.
This check ensures the filters are only called for the device on
the top of a stack. So, I probably should change the check to
sk == skb_to_full_sk(skb)
instead of removing it. If we remove the check, egress filters
could be called multiple times for a skb, just like what Daniel said.
Does that make sense?
[1]
https://lore.kernel.org/all/CAADnVQKi0c=Mf3b=z43=b6n2xBVhwPw4QoV_au5+pFE29iLkaQ@xxxxxxxxxxxxxx/
[2] https://lore.kernel.org/all/58193E9D.7040201@xxxxxxxxxxxxx/
Signed-off-by: Kui-Feng Lee <kuifeng@xxxxxxxx>
---
include/linux/bpf-cgroup.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/include/linux/bpf-cgroup.h b/include/linux/bpf-cgroup.h
index 57e9e109257e..e656da531f9f 100644
--- a/include/linux/bpf-cgroup.h
+++ b/include/linux/bpf-cgroup.h
@@ -199,7 +199,7 @@ static inline bool cgroup_bpf_sock_enabled(struct
sock *sk,
#define BPF_CGROUP_RUN_PROG_INET_EGRESS(sk, skb) \
({ \
int __ret = 0; \
- if (cgroup_bpf_enabled(CGROUP_INET_EGRESS) && sk && sk ==
skb->sk) { \
+ if (cgroup_bpf_enabled(CGROUP_INET_EGRESS) && sk) { \
typeof(sk) __sk = sk_to_full_sk(sk); \
if (sk_fullsock(__sk) && \
cgroup_bpf_sock_enabled(__sk,
CGROUP_INET_EGRESS)) \
