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SubjectRe: Linux 3.6
Hi Nick,

3.6 introduced link restrictions:
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux.git;a=commitdiff;h=800179c9b8a1e796e441674776d11cd4c05d61d7

It sounds like you've got symlinks in a world-writable directory, and
you're following those symlinks across mis-matched uids. You can either
have the symlinks be owned by the directory owner, or you can turn off
symlink restrictions in sysctl:

# echo 0 > /proc/sys/fs/protected_symlinks

-Kees

On Wed, Oct 03, 2012 at 03:46:14PM -0400, Nick Bowler wrote:
> On 2012-09-30 17:38 -0700, Linus Torvalds wrote:
> > So here it is, 3.6 final. Sure, I'd have been happier with even fewer
> > changes, but that just never happens. And holding off the release
> > until people get too bored to send me the small stuff just makes the
> > next merge window more painful.
>
> Just upgraded to 3.6 from 3.5, and now some of my kernel build scripts
> are throwing "permission denied" errors. Apparently symlinks are
> broken somehow?
>
> # id
> uid=0(root) gid=0(root) groups=0(root),1(bin),2(daemon),3(sys),4(adm),6(disk),10(wheel),11(floppy),20(dialout),26(tape),27(video)
>
> # ls -l /scratch_space/linux
> drwxr-xr-x 24 nbowler eng 4096 2012-10-03 13:41 /scratch_space/linux
>
> # readlink /scratch_space/linux-2.6
> linux
>
> # cd /scratch_space/linux
> # pwd
> /scratch_space/linux
>
> # cd /scratch_space/linux-2.6
> cd: permission denied: /scratch_space/linux-2.6
>
> WTF? 3.5 is fine. I will try to bisect this later, but I figured I'd
> throw this out there now in case anyone has any ideas...
>
> Cheers,
> --
> Nick Bowler, Elliptic Technologies (http://www.elliptictech.com/)
>
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--
Kees Cook @outflux.net


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