Re: [PATCH v2 2/4] net: af_unix: Useful handling of LSM denials on SCM_RIGHTS

[Kuniyuki Iwashima]

On Tue, Jun 16, 2026 at 7:29 AM Jori Koolstra <jkoolstra@xxxxxxxxx> wrote:
>
> Right now if some LSM such as Smack denies an AF_UNIX socket peer to
> receive an SCM_RIGHTS fd, the SCM_RIGHTS fd array will be cut short at
> that point, and MSG_CTRUNC is set on return of recvmsg(). 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.
>
> [1]: https://github.com/uapi-group/kernel-features#useful-handling-of-lsm-denials-on-scm_rights
>
> Signed-off-by: Jori Koolstra <jkoolstra@xxxxxxxxx>
> ---
>  fs/file.c                         | 48 ++++++++++++++++++++-----------
>  include/linux/file.h              |  2 ++
>  include/net/af_unix.h             |  1 +

net-next is closed during the merge window, so please repost after that.

a few comments: please

* add cover letter
* separate fs/ and net/ changes
* do not touch tools/testing/selftest/Makefile
* use kselftest_harness.h and system()
* check other local rules (reverse xmas tree order, etc) in
Documentation/process/maintainer-netdev.rst

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pw-bot: cr