PR/60832 CVS commit: src

["Taylor R Campbell" <riastradh%netbsd.org@localhost>]

The following reply was made to PR kern/60832; it has been noted by GNATS.

From: "Taylor R Campbell" <riastradh%netbsd.org@localhost>
To: gnats-bugs%gnats.NetBSD.org@localhost
Cc: 
Subject: PR/60832 CVS commit: src
Date: Fri, 2 Oct 2026 01:31:31 +0000

 Module Name:	src
 Committed By:	riastradh
 Date:		Fri Oct  2 01:31:31 UTC 2026
 
 Modified Files:
 	src/sys/kern: uipc_socket2.c
 	src/tests/kernel: t_fdpass.c
 
 Log Message:
 sendmsg(2): Don't fail with ENOBUFS on fd passing.
 
 We don't fail with ENOBUFS if we're not fd-passing -- we just block
 or fail earlier on with EAGAIN; no reason to invent a new failure
 mode just for the fd-passing case.
 
 Whether we should have _any_ path that checks the receiving socket's
 receive buffer limit is another question, but it's silly for it to:
 1. apply _only_ when passing fds,
 2. trip only when the kernel internally expands the buffer, and/or
 3. fail with ENOBUFS instead of blocking or failing with EAGAIN.
 
 This change essentially matches FreeBSD's subversion r337328:
 
 commit 5b0480f2cca0a4a04f21055ed769be93f11348de
 Author: Mark Johnston <markj%FreeBSD.org@localhost>
 Date:   Sat Aug 4 20:26:54 2018 +0000
 
     Don't check rcv sockbuf limits when sending on a unix stream socket.
 
     sosend_generic() performs an initial comparison of the amount of data
     (including control messages) to be transmitted with the send buffer
     size. When transmitting on a unix socket, we then compare the amount
     of data being sent with the amount of space in the receive buffer size;
     if insufficient space is available, sbappendcontrol() returns an error
     and the data is lost.  This is easily triggered by sending control
     messages together with an amount of data roughly equal to the send
     buffer size, since the control message size may change in uipc_send()
     as file descriptors are internalized.
 
     Fix the problem by removing the space check in sbappendcontrol(),
     whose only consumer is the unix sockets code.  The stream sockets code
     uses the SB_STOP mechanism to ensure that senders will block if the
     receive buffer fills up.
 
     PR:             181741
     MFC after:      1 month
     Sponsored by:   The FreeBSD Foundation
     Differential Revision:  https://reviews.freebsd.org/D16515
 
 https://cgit.freebsd.org/src/commit/?id=5b0480f2cca0a4a04f21055ed769be93f11348de
 
 PR kern/60832: AF_LOCAL stream: sendmsg() with SCM_RIGHTS silently
 drops data and descriptors but reports success
 
 
 To generate a diff of this commit:
 cvs rdiff -u -r1.148 -r1.149 src/sys/kern/uipc_socket2.c
 cvs rdiff -u -r1.3 -r1.4 src/tests/kernel/t_fdpass.c
 
 Please note that diffs are not public domain; they are subject to the
 copyright notices on the relevant files.