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SubjectRe: mm/sched/net: BUG when running simple code
On Fri, Jun 13, 2014 at 12:01:37AM -0400, Sasha Levin wrote:
> On 06/12/2014 11:27 PM, Dan Aloni wrote:
> > On Thu, Jun 12, 2014 at 10:56:16PM -0400, Sasha Levin wrote:
> >> > Hi all,
> >> >
> >> > Okay, I'm really lost. I got the following when fuzzing, and can't really explain what's
> >> > going on. It seems that we get a "unable to handle kernel paging request" when running
> >> > rather simple code, and I can't figure out how it would cause it.
> > [..]
> >> > Which agrees with the trace I got:
> >> >
> >> > [ 516.309720] BUG: unable to handle kernel paging request at ffffffffa0f12560
> >> > [ 516.309720] IP: netlink_getsockopt (net/netlink/af_netlink.c:2271)
> > [..]
> >> > [ 516.309720] RIP netlink_getsockopt (net/netlink/af_netlink.c:2271)
> >> > [ 516.309720] RSP <ffff8803fc85fed8>
> >> > [ 516.309720] CR2: ffffffffa0f12560
> >> >
> >> > They only theory I had so far is that netlink is a module, and has gone away while the code
> >> > was executing, but netlink isn't a module on my kernel.
> > The RIP - 0xffffffffa0f12560 is in the range (from Documentation/x86/x86_64/mm.txt):
> >
> > ffffffffa0000000 - ffffffffff5fffff (=1525 MB) module mapping space
> >
> > So seems it was in a module.
>
> Yup, that's why that theory came up, but when I checked my config:
> ...
> that theory went away. (also confirmed by not finding a netlink module.)
>
> What about the kernel .text overflowing into the modules space? The loader
> checks for that, but can something like that happen after everything is
> up and running? I'll look into that tomorrow.

another theory: Trinity can sometimes generate plausible looking module
addresses and pass those in structs etc.

I wonder if there's somewhere in that path that isn't checking that the address
in the optval it got is actually a userspace address before it tries to write to it.

Dave



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