Re: RFC: [PATCH] SCM_CREDS support 2(2)

[Svante Signell <svante.signell@gmail.com>]

Updated second patch, reflecting recent changes in the first patch.

On Tue, 2013-10-15 at 10:36 +0200, Svante Signell wrote:
> Hi,
> 
> Patch 2(2) on SCM_CREDS support for GNU/Hurd.
> 
> This patch is optional. kFreeBSD dos not support this case (but Linux
> is).
> 
> This patch implements the last cases in the test code sent to the list
> in September 2013, options <-n> and <-z> see
> http://lists.debian.org/debian-hurd/2013/09/msg00034.html 
> 
> Options:
> no flag:
> -z: send a zero credentials byte as data (used by dbus)
> -n: don't create explicit credentials structure
> 
> 1) Sent credentials and PID are correct:
> ./scm_cred_recv &
> ./scm_cred_send -n
> Linux: OK, only sent ids
> kFreeBSD: nOK; ERROR: bad cmsg header cmhp == NULL, data: OK
> Hurd: same as kFreeBSD
> 
> ./scm_cred_recv -z&
> ./scm_cred_send -nz
> Linux: OK, same as above
> kFreeBSD: nOK; ERROR: bad cmsg header cmhp == NULL, data: OK
> Hurd: OK, sent IDs + groups
> 
> 2) When no credentials structure is sent the behaviour is different:
> Linux:
> -n: received credentials are created
> -zn: received credentials ones are created
> 
> kFreeBSD: 
> -n: ERROR: bad cmsg header cmhp == NULL
> -zn: ERROR: bad cmsg header cmhp == NULL
> 
> Hurd:
> -n: ERROR: bad cmsg header cmhp == NULL
> -zn: received credentials are created
> 

--- a/sysdeps/mach/hurd/sendmsg.c
+++ b/sysdeps/mach/hurd/sendmsg.c
@@ -193,6 +193,48 @@
       goto label;
     }
 
+  /* Special case: message->msg_controllen <  sizeof (struct cmsghdr) */
+  /* Special case: cmsg == NULL and zero credentials byte sent */
+  else if (cmsg == NULL && (strncmp(data.ptr, "\0", 1) == 0))
+    {
+      union {
+	struct cmsghdr cmh;
+	char control[CMSG_SPACE(sizeof(struct cmsgcred))];
+	/* Space large enough to hold a cmsgcred structure */
+      } control_un;
+
+      struct msghdr msgh;
+      msgh.msg_name = NULL;
+      msgh.msg_namelen = 0;
+      msgh.msg_control = control_un.control;
+      msgh.msg_controllen = sizeof(control_un.control);
+      msgh.msg_flags = 0;
+
+      struct cmsghdr *cmhp = CMSG_FIRSTHDR(&msgh);
+      cmhp->cmsg_level = SOL_SOCKET;
+      cmhp->cmsg_type = SCM_CREDS;
+      cmhp->cmsg_len = CMSG_LEN(sizeof(struct cmsgcred));
+
+      ucredp = (struct cmsgcred *) CMSG_DATA(cmhp);
+      pids = __getpid();
+      euids = __geteuid();
+      auids = __getuid();
+      egids = __getegid();
+      agids = __getgid();
+      euidslen = auidslen = egidslen = agidslen = 1;
+
+      nports = 0;
+      control = control_un.control;
+      controllen = sizeof(control_un.control);
+
+      err = check_auth(pids, euids, euidslen, auids, auidslen,
+			egids, egidslen, agids, agidslen,
+			ucredp);
+      if (err)
+	return __hurd_fail (err);
+      goto label;
+    }
+
   /* SCM_RIGHTS support: get the number of fds to send.  */
   cmsg = CMSG_FIRSTHDR (message);
   for (; cmsg; cmsg = CMSG_NXTHDR (message, cmsg))