Subject: Re: [Eulerkernel] [PATCH] af_unix: dont send SCM_CREDENTIAL when dest socket is NULL

From: dingtianhong <[email-masked]>
Date: Tue, 26 Mar 2013 11:08:56 +0800

On 2013/3/25 22:04, Eric Dumazet wrote:
> On Mon, 2013-03-25 at 18:28 +0800, dingtianhong wrote:
>> SCM_SCREDENTIALS should apply to write() syscalls only either source or destination
>> socket asserted SOCK_PASSCRED. The original implememtation in maybe_add_creds is wrong,
>> and breaks several LSB testcases ( i.e. /tset/LSB.os/netowkr/recvfrom/T.recvfrom).
>>
>> Origionally-authored-by: Karel Srot <[email-masked]>
>> Signed-off-by: Ding Tianhong <[email-masked]>
>> ---
>>    net/unix/af_unix.c | 4 ++--
>>    1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
>> index 51be64f..99189fd 100644
>> --- a/net/unix/af_unix.c
>> +++ b/net/unix/af_unix.c
>> @@ -1413,8 +1413,8 @@ 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();
>>           }
> 
> I am not sure why adding credentials if other->sk_socket is NULL could
> break an application ?
The bugzilla has report the bug:https://lsbbugs.linuxfoundation.org/show_bug.cgi?id=3523

> 
> This was the case before commit introducing this code.

The commit 16e5726269(af_unix: dont send SCM_CREDENTIALS by default) may  introducing the problem.

> 
> Anyway patch looks fine
> 
> Acked-by: Eric Dumazet <[email-masked]>
> 
> 
> 
> 
> 
>