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From: Gleb Smirnoff <glebius@FreeBSD.org>
Date: Wed, 12 Sep 2012 09:50:18 +0000 (UTC)
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Subject: svn commit: r240385 - head/lib/libc/sys
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Author: glebius
Date: Wed Sep 12 09:50:17 2012
New Revision: 240385
URL: http://svn.freebsd.org/changeset/base/240385

Log:
  Describe in detail required conditions for receiving the SCM_CREDS
  control message and suggest to use LOCAL_CREDS setsockopt() for
  reliability.

Modified:
  head/lib/libc/sys/recv.2

Modified: head/lib/libc/sys/recv.2
==============================================================================
--- head/lib/libc/sys/recv.2	Wed Sep 12 09:29:22 2012	(r240384)
+++ head/lib/libc/sys/recv.2	Wed Sep 12 09:50:17 2012	(r240385)
@@ -28,7 +28,7 @@
 .\"     @(#)recv.2	8.3 (Berkeley) 2/21/94
 .\" $FreeBSD$
 .\"
-.Dd December 28, 2006
+.Dd September 12, 2012
 .Dt RECV 2
 .Os
 .Sh NAME
@@ -252,8 +252,21 @@ struct cmsgcred {
 };
 .Ed
 .Pp
-The kernel will fill in the credential information of the sending process
-and deliver it to the receiver.
+If a sender supplies ancillary data with enough space for the above struct
+tagged as
+.Dv SCM_CREDS
+control message type to the
+.Fn sendmsg
+system call, then kernel will fill in the credential information of the
+sending process and deliver it to the receiver.
+Since receiver usually has no control over a sender, this method of retrieving
+credential information isn't reliable.
+For reliable retrieval of remote side credentials it is advised to use the
+.Dv LOCAL_CREDS
+socket option on the receiving socket.
+See
+.Xr unix 4
+for details.
 .Pp
 The
 .Fa msg_flags
@@ -322,7 +335,8 @@ address space.
 .Xr getsockopt 2 ,
 .Xr read 2 ,
 .Xr select 2 ,
-.Xr socket 2
+.Xr socket 2 ,
+.Xr unix 4
 .Sh HISTORY
 The
 .Fn recv