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Merge branch 'net-af_unix-useful-handling-of-lsm-denials-on-scm_rights'

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Jori Koolstra says:

====================
net: af_unix: useful handling of LSM denials on SCM_RIGHTS

Right now if some LSM denies an AF_UNIX socket peer to receive a
SCM_RIGHTS fd, the SCM_RIGHTS fd array will be cut short at
that point, and MSG_CTRUNC is set on return of recvmsg(2). This is
highly problematic behaviour, because it leaves the receiver
wondering what happened. As per man page MSG_CTRUNC is supposed to
indicate that the control buffer was sized too short, but suddenly
a permission error might result in the exact same flag being set.
Moreover, the receiver has no chance to determine how many fds got
originally sent and how many were suppressed.[1]

Add a SO_RIGHTS_NOTRUNC option to UNIX sockets to enable more useful
handling of LSM denials when receiving SCM_RIGHTS messages: instead of
truncating the message at the first blocked fd, keep every fd slot
and store the LSM errno in the blocked slot. This option is inherited
by the accept()-ed socket when set on the listen() socket.

[1]: https://github.com/uapi-group/kernel-features#useful-handling-of-lsm-denials-on-scm_rights
====================

Link: https://patch.msgid.link/20260813162818.149248-1-jkoolstra@xs4all.nl
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Jakub Kicinski 2026-08-17 18:15:01 -07:00
commit f461b94f1a
15 changed files with 413 additions and 22 deletions
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