netdev - net: uninitialized loopback addr leaks to userspace

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-next>] [day] [month] [year] [list]

Message-ID: <19f34abd0905301323k1498ca3fv31b271de65d60afc@mail.gmail.com>
Date:	Sat, 30 May 2009 22:23:24 +0200
From:	Vegard Nossum <vegard.nossum@...il.com>
To:	Linux Netdev List <netdev@...r.kernel.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Pekka Enberg <penberg@...helsinki.fi>,
	LKML <linux-kernel@...r.kernel.org>
Subject: net: uninitialized loopback addr leaks to userspace

Hi,

It seems that loopback's hardware address is never initialized by the
kernel. So if userspace attempts to read this address before it has
been set, the kernel will return some uninitialized data (only 6
bytes, though). This can be demonstrated by creating a new network
namespace (CLONE_NEWNET), which creates a new loopback device, then
call ioctl() with SIOCGIFHWADDR on "lo". If this is done in a loop,
with some background load, or by running multiple instances, random
data will start to show up in the returned address.

[  406.750329] WARNING: kmemcheck: Caught 16-bit read from
uninitialized memory (ffff880007220974)
[  406.753555] 18a2d7060088ffff18a2d7060088ffff00000000010000000100000003000000
[  406.758862]  i i i i i i i i i i i i i i i i i u u u u u u u u u u u u u u u
[  406.766224]                                          ^
[  406.768792] Modules linked in:
[  406.770416] Pid: 757, comm: ifconfig Not tainted
2.6.30-rc7-next-20090529 #404
[  406.772876] RIP: 0010:[<ffffffff80664789>]  [<ffffffff80664789>]
dev_ioctl+0x5d9/0x600
[  406.804677]  [<ffffffff8064ff75>] sock_ioctl+0x95/0x2a0
[  406.807242]  [<ffffffff802c35eb>] vfs_ioctl+0x1b/0x70
[  406.809348]  [<ffffffff802c36fa>] do_vfs_ioctl+0x8a/0x570
[  406.811419]  [<ffffffff802c3c79>] sys_ioctl+0x99/0xa0
[  406.813400]  [<ffffffff802f3941>] dev_ifsioc+0x81/0x2f0
[  406.815424]  [<ffffffff802f454d>] compat_sys_ioctl+0xed/0x3c0
[  406.817596]  [<ffffffff8022d476>] cstar_dispatch+0x7/0x26
[  406.819978]  [<ffffffffffffffff>] 0xffffffffffffffff

This is the code that triggers the warning, in net/core/dev.c, around line 4150:

    memcpy(ifr->ifr_hwaddr.sa_data, dev->dev_addr,
        min(sizeof ifr->ifr_hwaddr.sa_data, (size_t) dev->addr_len));

So it's dev->dev_addr that is the pointer to the uninitialized data.

I didn't know how to fix it.


Vegard
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html