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Date: Wed, 11 Sep 2013 00:45:16 -0400 (EDT) From: Jason Wang <jasowang@...hat.com> To: "Michael S. Tsirkin" <mst@...hat.com> Cc: Wannes Rombouts <wannes.rombouts@...tech.eu>, davem@...emloft.net, edumazet@...gle.com, nhorman@...driver.com, netdev@...r.kernel.org, Kevin Soules <kevin.soules@...tech.eu> Subject: Re: Use-after-free in TUNSETIFF ----- Original Message ----- > On Wed, Sep 11, 2013 at 01:59:47AM +0200, Wannes Rombouts wrote: > > (I sent this email to security@...nel.org but they told me I should send > > it to you guys, so here you go.) > > > > Hi, > > > > I would like to report what I believe could be a potential CAP_NET_ADMIN > > to ring0 privilege escalation. > > > > The bug is in the way tuntap interfaces are initialized, when given an > > invalid name they cause a use after free. Also software like vmware > > allows for at least a freeze or kernel panic by a simple user but might > > also allow privilege escalation. > > > > Very simple to test, this causes a crash: > > # ip tuntap add dev %% mode tap > > If it doesn't crash immediately wait a few seconds and try again. > > > > > > We haven't managed to exploit the use after free yet, but we are still > > working on it. At least it crashes even with the latest kernel 3.11 and > > on different distros. (tested on Debian, Ubuntu and Arch) Looking at the > > source the bug seems quite old. > > > > > > Here is our analysis: > > > > A user with CAP_NET_ADMIN calls ioctl with TUNSETIFF and an invalid name > > for example "%d%d". > > > > tun_set_iff starts to initialize the tun_struct. > > http://lxr.free-electrons.com/source/drivers/net/tun.c#L1589 > > > > It calls tun_flow_init which starts a timer with tun_flow_cleanup as > > callback. http://lxr.free-electrons.com/source/drivers/net/tun.c#L852 > > > > After this tun_set_iff calls register_netdevice which returns an error > > because of the invalid name. > > > > This error causes the goto err_free_dev and the call to free_netdev. > > This will free the tun_struct. > > > > Later, once the callback gets called it uses bad memory. Sometimes it > > doesn’t get called because the timer_list has been compromised and we > > get a kernel panic at: > > http://lxr.free-electrons.com/source/kernel/timer.c?v=2.6.33#L949 > > > > But it is possible to get some memory from userland that overlaps only > > the beginning of the tun_struct without overwriting the timer_list > > because there is a big array before it. Then it might be possible to > > exploit tun_flow_cleanup when it is called, but we didn't succeed yet. > > > > ------------------------------------------------------------------------ > > > > > > This is the first time we try to exploit the kernel so we basically suck > > at this. I don't know if someone more skilled could do this easily or > > not, but we'll keep trying and I'll let you know if we manage it. > > > > In the mean time please let us know what you think of this and of course > > we are very interested in the way this is patched. Please keep us in the > > loop. > > > > Of course we will be happy to assist in any way we can, feel free to > > ask! Also we would like to know when you think it would be reasonable to > > disclose and talk about this bug. > > > > Regards, > > > > Wannes 'wapiflapi' Rombouts > > Kevin 'eax64' Soules > > > > > > > > Thanks a lot for the report. So this one is easy to fix I think. > Does the below patch help? > However, looking at the error handling in that function, > it looks like it could leak resources in many other ways. > We probably need more patches on top to fix it properly. > True, I'm working on a patch to solve all of them. Will post soon -- 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
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