Re: Linux 4.9.256

[Avi Kivity]

On 2/8/21 8:57 PM, Sasha Levin wrote:
> On Mon, Feb 08, 2021 at 05:50:21PM +0200, Avi Kivity wrote:
> > On 05/02/2021 16.26, Greg Kroah-Hartman wrote:
> > > I'm announcing the release of the 4.9.256 kernel.
> > >
> > > This, and the 4.4.256 release are a little bit "different" than normal.
> > >
> > > This contains only 1 patch, just the version bump from .255 to .256 
> > > which ends
> > > up causing the userspace-visable LINUX_VERSION_CODE to behave a bit 
> > > differently
> > > than normal due to the "overflow".
> > >
> > > With this release, KERNEL_VERSION(4, 9, 256) is the same as 
> > > KERNEL_VERSION(4, 10, 0).
> >
> >
> > I think this is a bad idea. Many kernel features can only be 
> > discovered by checking the kernel version. If a feature was 
> > introduced in 4.10, then an application can be tricked into thinking 
> > a 4.9 kernel has it.
> >
> >
> > IMO, better to stop LINUX_VERSION_CODE at 255 and introduce a 
>
> In the upstream (and new -stable fix) we did this part.
>
> > LINUX_VERSION_CODE_IMPROVED that has more bits for patchlevel.
>
> Do you have a usecase where it's actually needed? i.e. userspace that
> checks for -stable patchlevels?

Not stable patchlevels, but minors. So a change from 4.9 to 4.10 could 
be harmful.


I have two such examples (not on the 4.9->4.10 boundary), but they test 
the runtime version from uname(), not LINUX_VERSION_CODE, so they would 
be vulnerable to such a change.