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From: Dmitry Vyukov <dvyukov@google.com>
To: Paul Moore <paul@paul-moore.com>,
	stephen.smalley.work@gmail.com,
	Eric Paris <eparis@parisplace.org>,
	selinux@vger.kernel.org
Cc: LKML <linux-kernel@vger.kernel.org>,
	syzkaller <syzkaller@googlegroups.com>,
	Willem de Bruijn <willemb@google.com>
Subject: selinux_netlink_send changes program behavior
Date: Fri, 24 Apr 2020 10:27:25 +0200	[thread overview]
Message-ID: <CACT4Y+YTi4JCFRqOB9rgA22S+6xxTo87X41hj6Tdfro8K3ef7g@mail.gmail.com> (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?

Thanks

FTR, the C program is:
https://gist.githubusercontent.com/dvyukov/dda1c547ca9121817159d29afa72aea2/raw/41b021d722947df4d8c48e2fc783591b44671ceb/gistfile1.txt
kernel config:
https://gist.githubusercontent.com/dvyukov/08bf2c2fd873a84a2c4c771740716183/raw/78fb3b1063b7ae37625468f32868869edbd1bd19/gistfile1.txt
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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