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From: Dmitry Vyukov <>
To: Paul Moore <>,,
	Eric Paris <>,
Cc: LKML <>,
	syzkaller <>,
	Willem de Bruijn <>
Subject: selinux_netlink_send changes program behavior
Date: Fri, 24 Apr 2020 10:27:25 +0200	[thread overview]
Message-ID: <> (raw)

Hi SELinux maintainers,

We've hit a case where a developer wasn't able to reproduce a kernel
bug, it turned out to be a difference in behavior between SELinux and
non-SELinux kernels.
Condensed version: a program does sendmmsg on netlink socket with 2
mmsghdr's, first is completely empty/zeros, second contains some
actual payload. Without SELinux the first mmsghdr is treated as no-op
and the kernel processes the second one (triggers bug). However the
SELinux hook does:

static int selinux_netlink_send(struct sock *sk, struct sk_buff *skb)
    if (skb->len < NLMSG_HDRLEN) {
        err = -EINVAL;
        goto out;

and fails processing on the first empty mmsghdr (does not happen
without SELinux).

Is this difference in behavior intentional/acceptable/should be fixed?


FTR, the C program is:
kernel config:
on upstream commit 50cc09c1 it triggers a KASAN bug without SELinux,
but does not with SELinux.

             reply	other threads:[~2020-04-24  8:27 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-24  8:27 Dmitry Vyukov [this message]
2020-04-24 21:51 ` selinux_netlink_send changes program behavior Paul Moore
2020-04-25  5:14   ` Dmitry Vyukov
2020-04-25 11:42     ` Paul Moore
2020-04-25 12:00       ` Dmitry Vyukov
2020-04-28  1:53         ` Paul Moore

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