linux-kernel - Re: [Question] Should `CAP_NET_ADMIN` be needed when opening `/dev/ppp`?

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20160503101240.GA1304@alphalink.fr>
Date:	Tue, 3 May 2016 12:12:40 +0200
From:	Guillaume Nault <g.nault@...halink.fr>
To:	Wang Shanker <shankerwangmiao@...il.com>
Cc:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [Question] Should `CAP_NET_ADMIN` be needed when opening
 `/dev/ppp`?

On Sun, May 01, 2016 at 09:38:57PM +0800, Wang Shanker wrote:
> static int ppp_open(struct inode *inode, struct file *file)
> {
> 	/*
> 	 * This could (should?) be enforced by the permissions on /dev/ppp.
> 	 */
> 	if (!capable(CAP_NET_ADMIN))
> 		return -EPERM;
> 	return 0;
> }
> ```
> 
> I wonder why CAP_NET_ADMIN is needed here, rather than leaving it to the
> permission of the device node. If there is no need, I suggest that the
> CAP_NET_ADMIN check be removed.
> 
If this test was removed here, then it'd have to be added again in the
PPPIOCNEWUNIT ioctl, at the very least, because creating a netdevice
should require CAP_NET_ADMIN. Therefore that wouldn't help for your
case.
I don't know why the test was placed in ppp_open() in the first place,
but changing it now would have side effects on user space. So I'd
rather leave the code as is.