Re: [PATCH bpf-next v2] Only run BPF cgroup unix sockaddr recvmsg() hooks on named sockets

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From: Martin KaFai Lau <martin.lau@linux.dev>
Date: Mon, 16 Oct 2023 11:33:36 -0700
> On 10/12/23 11:11 AM, Kuniyuki Iwashima wrote:
> > From: Daan De Meyer <daan.j.demeyer@gmail.com>
> > Date: Thu, 12 Oct 2023 10:52:13 +0200
> >> Changes since v1:
> >>
> >> * Added missing Signed-off-by tag
> > 
> > You can put these after --- so that it will disappear when merged.
> > 
> > 
> >>
> >> We should not run the recvmsg() hooks on unnamed sockets as we do
> >> not run them on unnamed sockets in the other hooks either. We may
> >> look into relaxing this later but for now let's make sure we are
> >> consistent and not run the hooks on unnamed sockets anywhere.
> >>
> >> Signed-off-by: Daan De Meyer <daan.j.demeyer@gmail.com>
> >> ---
> >>   net/unix/af_unix.c | 14 ++++++++------
> >>   1 file changed, 8 insertions(+), 6 deletions(-)
> >>
> >> diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> >> index e10d07c76044..81fb8bddaff9 100644
> >> --- a/net/unix/af_unix.c
> >> +++ b/net/unix/af_unix.c
> >> @@ -2416,9 +2416,10 @@ int __unix_dgram_recvmsg(struct sock *sk, struct msghdr *msg, size_t size,
> >>   	if (msg->msg_name) {
> >>   		unix_copy_addr(msg, skb->sk);
> > 
> > How is an unnamed socket set to skb->sk ?
> 
> I had a similar question. Most likely socketpair? Please add an explanation in 
> the commit message in v3. Please also help to add a selftest for this case.

Ah exactly, socketpair() for SOCK_STREAM does it.


> 
> > 
> > 
> >>
> >> -		BPF_CGROUP_RUN_PROG_UNIX_RECVMSG_LOCK(sk,
> >> -						      msg->msg_name,
> >> -						      &msg->msg_namelen);
> >> +		if (msg->msg_namelen > 0)
> >> +			BPF_CGROUP_RUN_PROG_UNIX_RECVMSG_LOCK(sk,
> >> +							      msg->msg_name,
> >> +							      &msg->msg_namelen);
> >>   	}
> >>
> >>   	if (size > skb->len - skip)
> >> @@ -2773,9 +2774,10 @@ static int unix_stream_read_generic(struct unix_stream_read_state *state,
> >>   					 state->msg->msg_name);
> >>   			unix_copy_addr(state->msg, skb->sk);
> >>
> >> -			BPF_CGROUP_RUN_PROG_UNIX_RECVMSG_LOCK(sk,
> >> -							      state->msg->msg_name,
> >> -							      &state->msg->msg_namelen);
> >> +			if (state->msg->msg_namelen > 0)
> >> +				BPF_CGROUP_RUN_PROG_UNIX_RECVMSG_LOCK(sk,
> >> +								      state->msg->msg_name,
> >> +								      &state->msg->msg_namelen);
> >>
> >>   			sunaddr = NULL;
> >>   		}
> >> --
> >> 2.41.0