Subject: Re: [PATCH 1/2] Revert "af_unix: dont send SCM_CREDENTIAL when dest socket is NULL"

From: dingtianhong <[email-masked]>
Date: Thu, 4 Apr 2013 15:51:18 +0800

On 2013/4/4 10:13, Eric W. Biederman wrote:
> 
> This reverts commit 14134f6584212d585b310ce95428014b653dfaf6.
> 
> The problem that the above patch was meant to address is that af_unix
> messages are not being coallesced because we are sending unnecesarry
> credentials.  Not sending credentials in maybe_add_creds totally
> breaks unconnected unix domain sockets that wish to send credentails
> to other sockets.
> 

thanks for check the question and make a fix solution, but I still doubt that if unconnected unix
domain socket wish to send credentails to oher sockets, why dont set
SOCK_PASSCRED on sock->flags, I think the user need to decide the param
and shouldnt send creds by default way.

Ding

> In practice this break some versions of udev because they receive a
> message and the sending uid is bogus so they drop the message.
> 
> Cc: [email-masked]
> Reported-by: Sven Joachim <[email-masked]>
> Signed-off-by: "Eric W. Biederman" <[email-masked]>
> ---
>  net/unix/af_unix.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> index 971282b..f153a8d 100644
> --- a/net/unix/af_unix.c
> +++ b/net/unix/af_unix.c
> @@ -1412,8 +1412,8 @@ static void maybe_add_creds(struct sk_buff *skb, const struct socket *sock,
>  	if (UNIXCB(skb).cred)
>  		return;
>  	if (test_bit(SOCK_PASSCRED, &sock->flags) ||
> -	    (other->sk_socket &&
> -	    test_bit(SOCK_PASSCRED, &other->sk_socket->flags))) {
> +	    !other->sk_socket ||
> +	    test_bit(SOCK_PASSCRED, &other->sk_socket->flags)) {
>  		UNIXCB(skb).pid  = get_pid(task_tgid(current));
>  		UNIXCB(skb).cred = get_current_cred();
>  	}
>